Elite on the BBC Micro

# Elite D flight source [Elite-A]

``` ELITE D FILE

CODE_D% = P%

Type: Subroutine
Category: Market
Summary: Work out if we have space for one tonne of cargo
Context: See this subroutine on its own page
References: No direct references to this subroutine in this source file

Given a market item, work out whether there is room in the cargo hold for one
tonne of this item.

For standard tonne canisters, the limit is given by the type of cargo hold we
have, with a standard cargo hold having a capacity of 20t and an extended
cargo bay being 35t.

For items measured in kg (gold, platinum), g (gem-stones) and alien items,
the individual limit on each of these is 200 units.

Arguments:

A                    The type of market item (see QQ23 for a list of market
item numbers)

Returns:

A                    A = 1

C flag               Returns the result:

* Set if there is no room for this item

* Clear if there is room for this item

\ --- Mod: Original Acornsoft code removed: ----------->

\.tnpr1

\ STA QQ29              \ Store the type of market item in QQ29

\ LDA #1                \ Set the number of units of this market item to 1

\                       \ Fall through into tnpr to work out whether there is
\                       \ room in the cargo hold for A tonnes of the item of
\                       \ type QQ29

\ --- End of removed code ----------------------------->

Type: Subroutine
Category: Market
Summary: Work out if we have space for one tonne of cargo
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* Main flight loop (Part 8 of 16) calls tnpr1

Given a market item, work out whether there is room in the cargo hold for one
tonne of this item.

For standard tonne canisters, the limit is given by size of the cargo hold of
our current ship.

For items measured in kg (gold, platinum), g (gem-stones) and alien items,
there is no limit.

Arguments:

X                    The type of market item (see QQ23 for a list of market
item numbers)

Returns:

A                    The new number of items of type X in the hold

C flag               Returns the result:

* Set if there is no room for this item

* Clear if there is room for this item

\ --- Mod: Whole section added for Elite-A: ----------->

.tnpr1

CPX #16                \ If we are checking whether to add alien items (item
BEQ n_aliens           \ type 16), jump to n_aliens to skip the following two
\ instructions

CPX #13                \ If X >= 13, then X = 13, 14 or 15 (gold, platinum or
BCS l_2b04             \ gem-stones), for which there is no storage limit, so
\ jump to l_2b04 to signal that there is room for this
\ item

.n_aliens

LDY #12                \ Here we count the tonne canisters we have in the hold
\ and add 1 to see if we have enough room for one more
\ tonne of cargo, using Y as the loop counter, starting
\ with Y = 12

SEC                    \ Set the C flag, so the addition below has one extra,
\ representing the extra tonne we want to try to add

LDA QQ20+16            \ Set A to the number of alien items we already have in
\ the hold

.l_2af9

ADC QQ20,Y             \ Set A = A + the number of tonnes we have in the hold
\ of market item number Y

\ from the subroutine with the C flag set, as the hold

DEY                    \ Decrement the loop counter

BPL l_2af9             \ Loop back to add in the next market item in the hold,
\ until we have added up all market items from 12
\ (minerals) down to 0 (food)

CMP new_hold           \ If A < new_hold then the C flag will be clear (we have
\ room in the hold)
\
\ If A >= new_hold then the C flag will be set (we do
\ not have room in the hold)

.n_cargo

RTS                    \ Return from the subroutine

.l_2b04

\ If we get here then the item is gold, platinum or
\ gem-stones, for which there is no storage limit, and
\ the C flag is set

LDA QQ20,X             \ Set A to the number of units of this item that we
\ already have in the hold

ADC #0                 \ The C flag is set, so this adds one for the item we
\ just scooped

RTS                    \ Return from the subroutine

\ --- End of added section ---------------------------->

Type: Subroutine
Category: Universe
Summary: Twist the selected system's seeds four times
Deep dive: Twisting the system seeds
Galaxy and system seeds
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT111 calls TT20
* TT22 calls TT20
* TT23 calls TT20

Twist the three 16-bit seeds in QQ15 (selected system) four times, to
generate the next system.

.TT20

JSR P%+3               \ This line calls the line below as a subroutine, which
\ does two twists before returning here, and then we
\ fall through to the line below for another two
\ twists, so the net effect of these two consecutive
\ JSR calls is four twists, not counting the ones

JSR P%+3               \ This line calls TT54 as a subroutine to do a twist,
\ and then falls through into TT54 to do another twist
\ before returning from the subroutine

Type: Subroutine
Category: Universe
Summary: Twist the selected system's seeds
Deep dive: Twisting the system seeds
Galaxy and system seeds
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* cpl calls TT54

This routine twists the three 16-bit seeds in QQ15 once.

.TT54

LDA QQ15               \ X = tmp_lo = s0_lo + s1_lo
CLC
TAX

LDA QQ15+1             \ Y = tmp_hi = s1_hi + s1_hi + C
TAY

LDA QQ15+2             \ s0_lo = s1_lo
STA QQ15

LDA QQ15+3             \ s0_hi = s1_hi
STA QQ15+1

LDA QQ15+5             \ s1_hi = s2_hi
STA QQ15+3

LDA QQ15+4             \ s1_lo = s2_lo
STA QQ15+2

CLC                    \ s2_lo = X + s1_lo
TXA
STA QQ15+4

TYA                    \ s2_hi = Y + s1_hi + C
STA QQ15+5

RTS                    \ The twist is complete so return from the subroutine

Type: Subroutine
Category: Text
Summary: Print the distance to the selected system in light years
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT146
* TT25 calls TT146

If it is non-zero, print the distance to the selected system in light years.
If it is zero, just move the text cursor down a line.

Specifically, if the distance in QQ8 is non-zero, print token 31 ("DISTANCE"),
then a colon, then the distance to one decimal place, then token 35 ("LIGHT
YEARS"). If the distance is zero, move the cursor down one line.

.TT146

LDA QQ8                \ Take the two bytes of the 16-bit value in QQ8 and
ORA QQ8+1              \ OR them together to check whether there are any
BNE TT63               \ non-zero bits, and if so, jump to TT63 to print the
\ distance

INC YC                 \ The distance is zero, so we just move the text cursor
RTS                    \ in YC down by one line and return from the subroutine

.TT63

LDA #191               \ Print recursive token 31 ("DISTANCE") followed by
JSR TT68               \ a colon

LDX QQ8                \ Load (Y X) from QQ8, which contains the 16-bit
LDY QQ8+1              \ distance we want to show

SEC                    \ Set the C flag so that the call to pr5 will include a
\ decimal point, and display the value as (Y X) / 10

JSR pr5                \ Print (Y X) to 5 digits, including a decimal point

LDA #195               \ Set A to the recursive token 35 (" LIGHT YEARS") and
\ fall through into TT60 to print the token followed
\ by a paragraph break

Type: Subroutine
Category: Text
Summary: Print a text token and a paragraph break
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT213 calls TT60
* TT25 calls TT60

Print a text token (i.e. a character, control code, two-letter token or
recursive token). Then print a paragraph break (a blank line between
paragraphs) by moving the cursor down a line, setting Sentence Case, and then
printing a newline.

Arguments:

A                    The text token to be printed

.TT60

JSR TT27               \ Print the text token in A and fall through into TTX69
\ to print the paragraph break

Type: Subroutine
Category: Text
Summary: Print a paragraph break
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT25 calls TTX69

Print a paragraph break (a blank line between paragraphs) by moving the cursor
down a line, setting Sentence Case, and then printing a newline.

.TTX69

INC YC                 \ Move the text cursor down a line

\ Fall through into TT69 to set Sentence Case and print
\ a newline

Type: Subroutine
Category: Text
Summary: Set Sentence Case and print a newline
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT210 calls TT69

.TT69

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA #%10000000        \ Set bit 7 of QQ17 to switch to Sentence Case
\ STA QQ17

\ --- And replaced by: -------------------------------->

JSR vdu_80             \ Call vdu_80 to switch to Sentence Case

\ --- End of replacement ------------------------------>

\ Fall through into TT67 to print a newline

Type: Subroutine
Category: Text
Summary: Print a newline
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* CLYNS calls TT67
* plf calls TT67

.TT67

LDA #12                \ Load a newline character into A

JMP TT27               \ Print the text token in A and return from the
\ subroutine using a tail call

Type: Subroutine
Category: Text
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT25 calls TT70

This subroutine is called by TT25 when displaying a system's economy.

.TT70

LDA #173               \ Print recursive token 13 ("MAINLY ")
JSR TT27

JMP TT72               \ Jump to TT72 to continue printing system data as part
\ of routine TT25

Type: Subroutine
Category: Text
Summary: Print a text token followed by a space
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* STATUS calls spc
* TT25 calls spc

Print a text token (i.e. a character, control code, two-letter token or
recursive token) followed by a space.

Arguments:

A                    The text token to be printed

.spc

JSR TT27               \ Print the text token in A

JMP TT162              \ Print a space and return from the subroutine using a
\ tail call

Type: Subroutine
Category: Universe
Summary: Show the Data on System screen (red key f6) or Encyclopedia screen
(CTRL-f6)
Deep dive: Generating system data
Galaxy and system seeds
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT25
* TT70 calls entry point TT72

Other entry points:

TT72                 Used by TT70 to re-enter the routine after displaying
"MAINLY" for the economy type

.TT25

LDA #1                 \ Clear the top part of the screen, draw a white border,
JSR TT66               \ and set the current view type in QQ11 to 1

LDA #9                 \ Move the text cursor to column 9
STA XC

LDA #163               \ Print recursive token 3 as a title in capitals at
JSR TT27               \ the top ("DATA ON {selected system name}")

JSR NLIN               \ Draw a horizontal line underneath the title

JSR TTX69              \ Print a paragraph break and set Sentence Case

INC YC                 \ Move the text cursor down one more line

JSR TT146              \ If the distance to this system is non-zero, print
\ "DISTANCE", then the distance, "LIGHT YEARS" and a
\ paragraph break, otherwise just move the cursor down
\ a line

LDA #194               \ Print recursive token 34 ("ECONOMY") followed by
JSR TT68               \ a colon

LDA QQ3                \ The system economy is determined by the value in QQ3,
\ so fetch it into A. First we work out the system's
\ prosperity as follows:
\
\   QQ3 = 0 or 5 = %000 or %101 = Rich
\   QQ3 = 1 or 6 = %001 or %110 = Average
\   QQ3 = 2 or 7 = %010 or %111 = Poor
\   QQ3 = 3 or 4 = %011 or %100 = Mainly

CLC                    \ If (QQ3 + 1) >> 1 = %10, i.e. if QQ3 = %011 or %100
ADC #1                 \ (3 or 4), then call TT70, which prints "MAINLY " and
LSR A                  \ jumps down to TT72 to print the type of economy
CMP #%00000010
BEQ TT70

LDA QQ3                \ The LSR A above shifted bit 0 of QQ3 into the C flag,
BCC TT71               \ so this jumps to TT71 if bit 0 of QQ3 is 0, in other
\ words if QQ3 = %000, %001 or %010 (0, 1 or 2)

SBC #5                 \ Here QQ3 = %101, %110 or %111 (5, 6 or 7), so subtract
CLC                    \ 5 to bring it down to 0, 1 or 2 (the C flag is already
\ set so the SBC will be correct)

.TT71

ADC #170               \ A is now 0, 1 or 2, so print recursive token 10 + A.
JSR TT27               \ This means that:
\
\   QQ3 = 0 or 5 prints token 10 ("RICH ")
\   QQ3 = 1 or 6 prints token 11 ("AVERAGE ")
\   QQ3 = 2 or 7 prints token 12 ("POOR ")

.TT72

LDA QQ3                \ Now to work out the type of economy, which is
LSR A                  \ determined by bit 2 of QQ3, as follows:
LSR A                  \
\   QQ3 bit 2 = 0 = Industrial
\   QQ3 bit 2 = 1 = Agricultural
\
\ So we fetch QQ3 into A and set A = bit 2 of QQ3 using
\ two right shifts (which will work as QQ3 is only a
\ 3-bit number)

CLC                    \ Print recursive token 8 + A, followed by a paragraph
ADC #168               \ break and Sentence Case, so:
JSR TT60               \
\   QQ3 bit 2 = 0 prints token 8 ("INDUSTRIAL")
\   QQ3 bit 2 = 1 prints token 9 ("AGRICULTURAL")

LDA #162               \ Print recursive token 2 ("GOVERNMENT") followed by
JSR TT68               \ a colon

LDA QQ4                \ The system economy is determined by the value in QQ4,
\ so fetch it into A

CLC                    \ Print recursive token 17 + A, followed by a paragraph
ADC #177               \ break and Sentence Case, so:
JSR TT60               \
\   QQ4 = 0 prints token 17 ("ANARCHY")
\   QQ4 = 1 prints token 18 ("FEUDAL")
\   QQ4 = 2 prints token 19 ("MULTI-GOVERNMENT")
\   QQ4 = 3 prints token 20 ("DICTATORSHIP")
\   QQ4 = 4 prints token 21 ("COMMUNIST")
\   QQ4 = 5 prints token 22 ("CONFEDERACY")
\   QQ4 = 6 prints token 23 ("DEMOCRACY")
\   QQ4 = 7 prints token 24 ("CORPORATE STATE")

LDA #196               \ Print recursive token 36 ("TECH.LEVEL") followed by a
JSR TT68               \ colon

LDX QQ5                \ Fetch the tech level from QQ5 and increment it, as it
INX                    \ is stored in the range 0-14 but the displayed range
\ should be 1-15

\ --- Mod: Original Acornsoft code removed: ----------->

\ CLC                   \ Call pr2 to print the technology level as a 3-digit
\ JSR pr2               \ number without a decimal point (by clearing the C
\                       \ flag)

\ --- And replaced by: -------------------------------->

JSR pr2-1              \ Call pr2-1 to print the technology level as a 3-digit
\ number without a decimal point

\ --- End of replacement ------------------------------>

JSR TTX69              \ Print a paragraph break and set Sentence Case

LDA #192               \ Print recursive token 32 ("POPULATION") followed by a
JSR TT68               \ colon

SEC                    \ Call pr2 to print the population as a 3-digit number
LDX QQ6                \ with a decimal point (by setting the C flag), so the
JSR pr2                \ number printed will be population / 10

LDA #198               \ Print recursive token 38 (" BILLION"), followed by a
JSR TT60               \ paragraph break and Sentence Case

LDA #'('               \ Print an opening bracket
JSR TT27

LDA QQ15+4             \ Now to calculate the species, so first check bit 7 of
BMI TT75               \ s2_lo, and if it is set, jump to TT75 as this is an
\ alien species

LDA #188               \ Bit 7 of s2_lo is clear, so print recursive token 28
JSR TT27               \ ("HUMAN COLONIAL")

JMP TT76               \ Jump to TT76 to print "S)" and a paragraph break, so
\ the whole species string is "(HUMAN COLONIALS)"

.TT75

LDA QQ15+5             \ This is an alien species, and we start with the first
LSR A                  \ adjective, so fetch bits 2-7 of s2_hi into A and push
LSR A                  \ onto the stack so we can use this later
PHA

AND #%00000111         \ Set A = bits 0-2 of A (so that's bits 2-4 of s2_hi)

BCS TT205

ADC #227               \ Otherwise A = 0, 1 or 2, so print recursive token
JSR spc                \ 67 + A, followed by a space, so:
\
\   A = 0 prints token 67 ("LARGE") and a space
\   A = 1 prints token 67 ("FIERCE") and a space
\   A = 2 prints token 67 ("SMALL") and a space

.TT205

PLA                    \ Now for the second adjective, so restore A to bits
LSR A                  \ 2-7 of s2_hi, and throw away bits 2-4 to leave
LSR A                  \ A = bits 5-7 of s2_hi
LSR A

BCS TT206

ADC #230               \ Otherwise A = 0 to 5, so print recursive token
JSR spc                \ 70 + A, followed by a space, so:
\
\   A = 0 prints token 70 ("GREEN") and a space
\   A = 1 prints token 71 ("RED") and a space
\   A = 2 prints token 72 ("YELLOW") and a space
\   A = 3 prints token 73 ("BLUE") and a space
\   A = 4 prints token 74 ("BLACK") and a space
\   A = 5 prints token 75 ("HARMLESS") and a space

.TT206

LDA QQ15+3             \ Now for the third adjective, so EOR the high bytes of
EOR QQ15+1             \ s0 and s1 and extract bits 0-2 of the result:
AND #%00000111         \
STA QQ19               \   A = (s0_hi EOR s1_hi) AND %111
\
\ storing the result in QQ19 so we can use it later

BCS TT207

ADC #236               \ Otherwise A = 0 to 5, so print recursive token
JSR spc                \ 76 + A, followed by a space, so:
\
\   A = 0 prints token 76 ("SLIMY") and a space
\   A = 1 prints token 77 ("BUG-EYED") and a space
\   A = 2 prints token 78 ("HORNED") and a space
\   A = 3 prints token 79 ("BONY") and a space
\   A = 4 prints token 80 ("FAT") and a space
\   A = 5 prints token 81 ("FURRY") and a space

.TT207

LDA QQ15+5             \ Now for the actual species, so take bits 0-1 of
AND #%00000011         \ s2_hi, add this to the value of A that we used for
CLC                    \ the third adjective, and take bits 0-2 of the result
AND #%00000111

ADC #242               \ A = 0 to 7, so print recursive token 82 + A, so:
JSR TT27               \
\   A = 0 prints token 76 ("RODENT")
\   A = 1 prints token 76 ("FROG")
\   A = 2 prints token 76 ("LIZARD")
\   A = 3 prints token 76 ("LOBSTER")
\   A = 4 prints token 76 ("BIRD")
\   A = 5 prints token 76 ("HUMANOID")
\   A = 6 prints token 76 ("FELINE")
\   A = 7 prints token 76 ("INSECT")

.TT76

LDA #'S'               \ Print an "S" to pluralise the species
JSR TT27

LDA #')'               \ And finally, print a closing bracket, followed by a
JSR TT60               \ paragraph break and Sentence Case, to end the species
\ section

LDA #193               \ Print recursive token 33 ("GROSS PRODUCTIVITY"),
JSR TT68               \ followed by colon

LDX QQ7                \ Fetch the 16-bit productivity value from QQ7 into
LDY QQ7+1              \ (Y X)

JSR pr6                \ Print (Y X) to 5 digits with no decimal point

JSR TT162              \ Print a space

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA #0                \ Set QQ17 = 0 to switch to ALL CAPS
\ STA QQ17

\ --- And replaced by: -------------------------------->

JSR vdu_00             \ Call vdu_00 to switch to ALL CAPS

\ --- End of replacement ------------------------------>

LDA #'M'               \ Print "M"
JSR TT27

LDA #226               \ Print recursive token 66 (" CR"), followed by a
JSR TT60               \ paragraph break and Sentence Case

LDA #250               \ Print recursive token 90 ("AVERAGE RADIUS"), followed
JSR TT68               \ by a colon

\ The average radius is calculated like this:
\
\   ((s2_hi AND %1111) + 11) * 256 + s1_hi
\
\ or, in terms of memory locations:
\
\   ((QQ15+5 AND %1111) + 11) * 256 + QQ15+3
\
\ Because the multiplication is by 256, this is the
\ same as saying a 16-bit number, with high byte:
\
\   (QQ15+5 AND %1111) + 11
\
\ and low byte:
\
\   QQ15+3
\
\ so we can set this up in (Y X) and call the pr5
\ routine to print it out

LDA QQ15+5             \ Set A = QQ15+5
LDX QQ15+3             \ Set X = QQ15+3

AND #%00001111         \ Set Y = (A AND %1111) + 11
CLC
TAY

JSR pr5                \ Print (Y X) to 5 digits, not including a decimal
\ point, as the C flag will be clear (as the maximum
\ radius will always fit into 16 bits)

JSR TT162              \ Print a space

LDA #'k'               \ Print "km", returning from the subroutine using a
JSR TT26               \ tail call
LDA #'m'
JMP TT26

Type: Subroutine
Category: Universe
Summary: Calculate system data from the system seeds
Deep dive: Generating system data
Galaxy and system seeds
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT111 calls TT24

Calculate system data from the seeds in QQ15 and store them in the relevant
locations. Specifically, this routine calculates the following from the three
16-bit seeds in QQ15 (using only s0_hi, s1_hi and s1_lo):

QQ3 = economy (0-7)
QQ4 = government (0-7)
QQ5 = technology level (0-14)
QQ6 = population * 10 (1-71)
QQ7 = productivity (96-62480)

The ranges of the various values are shown in brackets. Note that the radius
and type of inhabitant are calculated on-the-fly in the TT25 routine when
the system data gets displayed, so they aren't calculated here.

.TT24

LDA QQ15+1             \ Fetch s0_hi and extract bits 0-2 to determine the
AND #%00000111         \ system's economy, and store in QQ3
STA QQ3

LDA QQ15+2             \ Fetch s1_lo and extract bits 3-5 to determine the
LSR A                  \ system's government, and store in QQ4
LSR A
LSR A
AND #%00000111
STA QQ4

LSR A                  \ If government isn't anarchy or feudal, skip to TT77,
BNE TT77               \ as we need to fix the economy of anarchy and feudal
\ systems so they can't be rich

LDA QQ3                \ Set bit 1 of the economy in QQ3 to fix the economy
ORA #%00000010         \ for anarchy and feudal governments
STA QQ3

.TT77

LDA QQ3                \ Now to work out the tech level, which we do like this:
EOR #%00000111         \
CLC                    \   flipped_economy + (s1_hi AND %11) + (government / 2)
STA QQ5                \
\ or, in terms of memory locations:
\
\   QQ5 = (QQ3 EOR %111) + (QQ15+3 AND %11) + (QQ4 / 2)
\
\ We start by setting QQ5 = QQ3 EOR %111

LDA QQ15+3             \ We then take the first 2 bits of s1_hi (QQ15+3) and
AND #%00000011         \ add it into QQ5
STA QQ5

LDA QQ4                \ And finally we add QQ4 / 2 and store the result in
LSR A                  \ QQ5, using LSR then ADC to divide by 2, which rounds
ADC QQ5                \ up the result for odd-numbered government types
STA QQ5

ASL A                  \ Now to work out the population, like so:
ASL A                  \
ADC QQ3                \   (tech level * 4) + economy + government + 1
ADC #1                 \ or, in terms of memory locations:
STA QQ6                \
\   QQ6 = (QQ5 * 4) + QQ3 + QQ4 + 1

LDA QQ3                \ Finally, we work out productivity, like this:
EOR #%00000111         \
ADC #3                 \  (flipped_economy + 3) * (government + 4)
STA P                  \                        * population
LDA QQ4                \                        * 8
STA Q                  \ or, in terms of memory locations:
JSR MULTU              \
\   QQ7 = (QQ3 EOR %111 + 3) * (QQ4 + 4) * QQ6 * 8
\
\ We do the first step by setting P to the first
\ expression in brackets and Q to the second, and
\ calling MULTU, so now (A P) = P * Q. The highest this
\ can be is 10 * 11 (as the maximum values of economy
\ and government are 7), so the high byte of the result
\ will always be 0, so we actually have:
\
\   P = P * Q
\     = (flipped_economy + 3) * (government + 4)

LDA QQ6                \ We now take the result in P and multiply by the
STA Q                  \ population to get the productivity, by setting Q to
JSR MULTU              \ the population from QQ6 and calling MULTU again, so
\ now we have:
\
\   (A P) = P * population

ASL P                  \ Next we multiply the result by 8, as a 16-bit number,
ROL A                  \ so we shift both bytes to the left three times, using
ASL P                  \ the C flag to carry bits from bit 7 of the low byte
ROL A                  \ into bit 0 of the high byte
ASL P
ROL A

STA QQ7+1              \ Finally, we store the productivity in two bytes, with
LDA P                  \ the low byte in QQ7 and the high byte in QQ7+1
STA QQ7

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Charts
Summary: Show the Long-range Chart (red key f4)
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT22
* TT114 calls TT22

.TT22

LDA #64                \ Clear the top part of the screen, draw a white border,
JSR TT66               \ and set the current view type in QQ11 to 32 (Long-
\ range Chart)

LDA #7                 \ Move the text cursor to column 7
STA XC

JSR TT81               \ Set the seeds in QQ15 to those of system 0 in the
\ current galaxy (i.e. copy the seeds from QQ21 to QQ15)

LDA #199               \ Print recursive token 39 ("GALACTIC CHART{galaxy
JSR TT27               \ number right-aligned to width 3}")

JSR NLIN               \ Draw a horizontal line at pixel row 23 to box in the
\ title and act as the top frame of the chart, and move
\ the text cursor down one line

LDA #152               \ Draw a screen-wide horizontal line at pixel row 152
JSR NLIN2              \ for the bottom edge of the chart, so the chart itself
\ is 128 pixels high, starting on row 24 and ending on
\ row 151

JSR TT14               \ Call TT14 to draw a circle with crosshairs at the
\ current system's galactic coordinates

LDX #0                 \ We're now going to plot each of the galaxy's systems,
\ so set up a counter in X for each system, starting at
\ 0 and looping through to 255

.TT83

STX XSAV               \ Store the counter in XSAV

LDX QQ15+3             \ Fetch the s1_hi seed into X, which gives us the
\ galactic x-coordinate of this system

LDY QQ15+4             \ Fetch the s2_lo seed and set bits 4 and 6, storing the
TYA                    \ result in ZZ to give a random number between 80 and
ORA #%01010000         \ (but which will always be the same for this system).
STA ZZ                 \ We use this value to determine the size of the point
\ for this system on the chart by passing it as the
\ distance argument to the PIXEL routine below

LDA QQ15+1             \ Fetch the s0_hi seed into A, which gives us the
\ galactic y-coordinate of this system

LSR A                  \ We halve the y-coordinate because the galaxy in
\ in Elite is rectangular rather than square, and is
\ twice as wide (x-axis) as it is high (y-axis), so the
\ chart is 256 pixels wide and 128 high

CLC                    \ Add 24 to the halved y-coordinate and store in XX15+1
ADC #24                \ (as the top of the chart is on pixel row 24, just
STA XX15+1             \ below the line we drew on row 23 above)

JSR PIXEL              \ Call PIXEL to draw a point at (X, A), with the size of
\ the point dependent on the distance specified in ZZ
\ (so a high value of ZZ will produce a 1-pixel point,
\ a medium value will produce a 2-pixel dash, and a
\ small value will produce a 4-pixel square)

JSR TT20               \ We want to move on to the next system, so call TT20
\ to twist the three 16-bit seeds in QQ15

LDX XSAV               \ Restore the loop counter from XSAV

INX                    \ Increment the counter

BNE TT83               \ If X > 0 then we haven't done all 256 systems yet, so
\ loop back up to TT83

LDA QQ9                \ Set QQ19 to the selected system's x-coordinate
STA QQ19

LDA QQ10               \ Set QQ19+1 to the selected system's y-coordinate,
LSR A                  \ halved to fit it into the chart
STA QQ19+1

LDA #4                 \ Set QQ19+2 to size 4 for the crosshairs size
STA QQ19+2

\ Fall through into TT15 to draw crosshairs of size 4 at
\ the selected system's coordinates

Type: Subroutine
Category: Drawing lines
Summary: Draw a set of crosshairs
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* SIGHT calls TT15
* TT103 calls TT15
* TT105 calls TT15
* TT14 calls TT15

For all views except the Short-range Chart, the centre is drawn 24 pixels to
the right of the y-coordinate given.

Arguments:

QQ19                 The pixel x-coordinate of the centre of the crosshairs

QQ19+1               The pixel y-coordinate of the centre of the crosshairs

QQ19+2               The size of the crosshairs

.TT15

LDA #24                \ Set A to 24, which we will use as the minimum
\ screen indent for the crosshairs (i.e. the minimum
\ distance from the top-left corner of the screen)

LDX QQ11               \ If the current view is not the Short-range Chart,
BPL P%+4               \ which is the only view with bit 7 set, then skip the
\ following instruction

LDA #0                 \ This is the Short-range Chart, so set A to 0, so the
\ crosshairs can go right up against the screen edges

STA QQ19+5             \ Set QQ19+5 to A, which now contains the correct indent
\ for this view

LDA QQ19               \ Set A = crosshairs x-coordinate - crosshairs size
SEC                    \ to get the x-coordinate of the left edge of the
SBC QQ19+2             \ crosshairs

BCS TT84               \ If the above subtraction didn't underflow, then A is
\ positive, so skip the next instruction

LDA #0                 \ The subtraction underflowed, so set A to 0 so the
\ crosshairs don't spill out of the left of the screen

.TT84

\ In the following, the authors have used XX15 for
\ temporary storage. XX15 shares location with X1, Y1,
\ X2 and Y2, so in the following, you can consider
\ the variables like this:
\
\   XX15   is the same as X1
\   XX15+1 is the same as Y1
\   XX15+2 is the same as X2
\   XX15+3 is the same as Y2
\
\ Presumably this routine was written at a different
\ time to the line-drawing routine, before the two
\ workspaces were merged to save space

STA XX15               \ Set XX15 (X1) = A (the x-coordinate of the left edge
\ of the crosshairs)

LDA QQ19               \ Set A = crosshairs x-coordinate + crosshairs size
CLC                    \ to get the x-coordinate of the right edge of the

BCC P%+4               \ If the above addition didn't overflow, then A is
\ correct, so skip the next instruction

LDA #255               \ The addition overflowed, so set A to 255 so the
\ crosshairs don't spill out of the right of the screen
\ (as 255 is the x-coordinate of the rightmost pixel
\ on-screen)

STA XX15+2             \ Set XX15+2 (X2) = A (the x-coordinate of the right
\ edge of the crosshairs)

LDA QQ19+1             \ Set XX15+1 (Y1) = crosshairs y-coordinate + indent
CLC                    \ to get the y-coordinate of the centre of the
STA XX15+1

JSR HLOIN              \ Draw a horizontal line from (X1, Y1) to (X2, Y1),
\ which will draw from the left edge of the crosshairs
\ to the right edge, through the centre of the
\ crosshairs

LDA QQ19+1             \ Set A = crosshairs y-coordinate - crosshairs size
SEC                    \ to get the y-coordinate of the top edge of the
SBC QQ19+2             \ crosshairs

BCS TT86               \ If the above subtraction didn't underflow, then A is
\ correct, so skip the next instruction

LDA #0                 \ The subtraction underflowed, so set A to 0 so the
\ crosshairs don't spill out of the top of the screen

.TT86

CLC                    \ Set XX15+1 (Y1) = A + indent to get the y-coordinate
ADC QQ19+5             \ of the top edge of the indented crosshairs
STA XX15+1

LDA QQ19+1             \ Set A = crosshairs y-coordinate + crosshairs size
CLC                    \ + indent to get the y-coordinate of the bottom edge
ADC QQ19+2             \ of the indented crosshairs

CMP #152               \ If A < 152 then skip the following, as the crosshairs
BCC TT87               \ won't spill out of the bottom of the screen

LDX QQ11               \ A >= 152, so we need to check whether this will fit in
\ this view, so fetch the view number

BMI TT87               \ If this is the Short-range Chart then the y-coordinate

LDA #151               \ Otherwise this is the Long-range Chart, so we need to
\ clip the crosshairs at a maximum y-coordinate of 151

.TT87

STA XX15+3             \ Set XX15+3 (Y2) = A (the y-coordinate of the bottom
\ edge of the crosshairs)

LDA QQ19               \ Set XX15 (X1) = the x-coordinate of the centre of the
STA XX15               \ crosshairs

STA XX15+2             \ Set XX15+2 (X2) = the x-coordinate of the centre of
\ the crosshairs

JMP LL30               \ Draw a vertical line (X1, Y1) to (X2, Y2), which will
\ draw from the top edge of the crosshairs to the bottom
\ edge, through the centre of the crosshairs, returning
\ from the subroutine using a tail call

Type: Subroutine
Category: Drawing circles
Summary: Draw a circle with crosshairs on a chart
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT22 calls TT14
* TT23 calls TT14

Draw a circle with crosshairs at the current system's galactic coordinates.

.TT126

LDA #104               \ Set QQ19 = 104, for the x-coordinate of the centre of
STA QQ19               \ the fixed circle on the Short-range Chart

LDA #90                \ Set QQ19+1 = 90, for the y-coordinate of the centre of
STA QQ19+1             \ the fixed circle on the Short-range Chart

LDA #16                \ Set QQ19+2 = 16, the size of the crosshairs on the
STA QQ19+2             \ Short-range Chart

JSR TT15               \ Draw the set of crosshairs defined in QQ19, at the
\ exact coordinates as this is the Short-range Chart

LDA QQ14               \ Set K to the fuel level from QQ14, so this can act as
STA K                  \ the circle's radius (70 being a full tank)

JMP TT128              \ Jump to TT128 to draw a circle with the centre at the
\ same coordinates as the crosshairs, (QQ19, QQ19+1),
\ and radius K that reflects the current fuel levels,
\ returning from the subroutine using a tail call

.TT14

LDA QQ11               \ If the current view is the Short-range Chart, which
BMI TT126              \ is the only view with bit 7 set, then jump up to TT126
\ to draw the crosshairs and circle for that view

\ Otherwise this is the Long-range Chart, so we draw the
\ crosshairs and circle for that view instead

LDA QQ14               \ Set K to the fuel level from QQ14 divided by 4, so
LSR A                  \ this can act as the circle's radius (70 being a full
LSR A                  \ tank, which divides down to a radius of 17)
STA K

LDA QQ0                \ Set QQ19 to the x-coordinate of the current system,
STA QQ19               \ which will be the centre of the circle and crosshairs
\ we draw

LDA QQ1                \ Set QQ19+1 to the y-coordinate of the current system,
LSR A                  \ halved because the galactic chart is half as high as
STA QQ19+1             \ it is wide, which will again be the centre of the
\ circle and crosshairs we draw

LDA #7                 \ Set QQ19+2 = 7, the size of the crosshairs on the
STA QQ19+2             \ Long-range Chart

JSR TT15               \ Draw the set of crosshairs defined in QQ19, which will
\ be drawn 24 pixels to the right of QQ19+1

LDA QQ19+1             \ Add 24 to the y-coordinate of the crosshairs in QQ19+1
CLC                    \ so that the centre of the circle matches the centre
ADC #24                \ of the crosshairs
STA QQ19+1

\ Fall through into TT128 to draw a circle with the
\ centre at the same coordinates as the crosshairs,
\ (QQ19, QQ19+1), and radius K that reflects the
\ current fuel levels

Type: Subroutine
Category: Drawing circles
Summary: Draw a circle on a chart
Deep dive: Drawing circles
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT14 calls TT128

Draw a circle with the centre at (QQ19, QQ19+1) and radius K.

Arguments:

QQ19                 The x-coordinate of the centre of the circle

QQ19+1               The y-coordinate of the centre of the circle

K                    The radius of the circle

.TT128

LDA QQ19               \ Set K3 = the x-coordinate of the centre
STA K3

LDA QQ19+1             \ Set K4 = the y-coordinate of the centre
STA K4

LDX #0                 \ Set the high bytes of K3(1 0) and K4(1 0) to 0
STX K4+1
STX K3+1

INX                    \ Set LSP = 1 to reset the ball line heap
STX LSP

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDX #2                \ Set STP = 2, the step size for the circle
\ STX STP

\ JSR CIRCLE2           \ Call CIRCLE2 to draw a circle with the centre at
\                       \ (K3(1 0), K4(1 0)) and radius K

\ RTS                   \ Return from the subroutine

\ --- And replaced by: -------------------------------->

INX                    \ Set STP = 2, the step size for the circle
STX STP

JMP CIRCLE2            \ Jump to CIRCLE2 to draw a circle with the centre at
\ (K3(1 0), K4(1 0)) and radius K, returning from the
\ subroutine using a tail call

\ --- End of replacement ------------------------------>

Type: Subroutine
Category: Inventory
Summary: Show a list of current cargo in our hold, optionally to sell
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT213 calls TT210

Show a list of current cargo in our hold, either with the ability to sell (the
Sell Cargo screen) or without (the Inventory screen), depending on the current
view.

Arguments:

QQ11                 The current view:

* 4 = Sell Cargo

* 8 = Inventory

.TT210

LDY #0                 \ We're going to loop through all the available market
\ items and check whether we have any in the hold (and,
\ if we are in the Sell Cargo screen, whether we want
\ to sell any items), so we set up a counter in Y to
\ denote the current item and start it at 0

.TT211

STY QQ29               \ Store the current item number in QQ29

LDX QQ20,Y             \ Fetch into X the amount of the current item that we
BEQ TT212              \ have in our cargo hold, which is stored in QQ20+Y,
\ and if there are no items of this type in the hold,

TYA                    \ Set Y = Y * 4, so this will act as an index into the
ASL A                  \ market prices table at QQ23 for this item (as there
ASL A                  \ are four bytes per item in the table)
TAY

LDA QQ23+1,Y           \ Fetch byte #1 from the market prices table for the
STA QQ19+1             \ current item and store it in QQ19+1, for use by the
\ call to TT152 below

TXA                    \ Store the amount of item in the hold (in X) on the
PHA                    \ stack

JSR TT69               \ Call TT69 to set Sentence Case and print a newline

CLC                    \ Print recursive token 48 + QQ29, which will be in the
LDA QQ29               \ range 48 ("FOOD") to 64 ("ALIEN ITEMS"), so this
ADC #208               \ prints the current item's name
JSR TT27

LDA #14                \ Move the text cursor to column 14, for the item's
STA XC                 \ quantity

PLA                    \ Restore the amount of item in the hold into X
TAX

\ --- Mod: Original Acornsoft code removed: ----------->

\ CLC                   \ Print the 8-bit number in X to 3 digits, without a
\ JSR pr2               \ decimal point

\ --- And replaced by: -------------------------------->

JSR pr2-1              \ Print the 8-bit number in X to 3 digits, without a
\ decimal point

\ --- End of replacement ------------------------------>

JSR TT152              \ Print the unit ("t", "kg" or "g") for the market item
\ whose byte #1 from the market prices table is in
\ QQ19+1 (which we set up above)

.TT212

LDY QQ29               \ Fetch the item number from QQ29 into Y, and increment
INY                    \ Y to point to the next item

CPY #17                \ If Y < 17 then loop back to TT211 to print the next
BCC TT211              \ item in the hold

RTS                    \ Otherwise return from the subroutine

Type: Subroutine
Category: Inventory
Summary: Show the Inventory screen (red key f9)
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT213

.TT213

LDA #8                 \ Clear the top part of the screen, draw a white border,
JSR TT66               \ and set the current view type in QQ11 to 8 (Inventory
\ screen)

LDA #11                \ Move the text cursor to column 11 to print the screen
STA XC                 \ title

LDA #164               \ Print recursive token 4 ("INVENTORY{crlf}") followed
JSR TT60               \ by a paragraph break and Sentence Case

JSR NLIN4              \ Draw a horizontal line at pixel row 19 to box in the
\ title. The authors could have used a call to NLIN3
\ instead and saved the above call to TT60, but you
\ just can't optimise everything

JSR fwl                \ Call fwl to print the fuel and cash levels on two
\ separate lines

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA CRGO              \ If our ship's cargo capacity is < 26 (i.e. we do not
\ CMP #26               \ have a cargo bay extension), skip the following two
\ BCC P%+7              \ instructions

\ LDA #107              \ We do have a cargo bay extension, so print recursive
\ JSR TT27              \ token 107 ("LARGE CARGO{sentence case} BAY")

\ --- And replaced by: -------------------------------->

LDA #14                \ Print recursive token 128 ("SPACE") followed by a
JSR TT68               \ colon

LDX new_hold           \ Set X to the amount of free space in our current
DEX                    \ ship's hold, minus 1 as new_hold contains the amount
\ of free space plus 1

JSR pr2-1              \ Call pr2-1 to print the amount of free space as a
\ 3-digit number without a decimal point

JSR TT160              \ Print "t" (for tonne) and a space

\ --- End of replacement ------------------------------>

JMP TT210              \ Jump to TT210 to print the contents of our cargo bay
\ and return from the subroutine using a tail call

Type: Subroutine
Category: Charts
Summary: Move the crosshairs on a chart
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT16

Move the chart crosshairs by the amount in X and Y.

Arguments:

X                    The amount to move the crosshairs in the x-axis

Y                    The amount to move the crosshairs in the y-axis

.TT16

TXA                    \ Push the change in X onto the stack (let's call this
PHA                    \ the x-delta)

DEY                    \ Negate the change in Y and push it onto the stack
TYA                    \ (let's call this the y-delta)
EOR #&FF
PHA

\ --- Mod: Original Acornsoft code removed: ----------->

\ JSR WSCAN             \ Call WSCAN to wait for the vertical sync, so the whole
\                       \ screen gets drawn and we can move the crosshairs with
\                       \ no screen flicker

\ --- End of removed code ----------------------------->

JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
\ which will erase the crosshairs currently there

PLA                    \ Store the y-delta in QQ19+3 and fetch the current
STA QQ19+3             \ y-coordinate of the crosshairs from QQ10 into A, ready
LDA QQ10               \ for the call to TT123

JSR TT123              \ Call TT123 to move the selected system's galactic
\ y-coordinate by the y-delta, putting the new value in
\ QQ19+4

LDA QQ19+4             \ Store the updated y-coordinate in QQ10 (the current
STA QQ10               \ y-coordinate of the crosshairs)

STA QQ19+1             \ This instruction has no effect, as QQ19+1 is
\ overwritten below, both in TT103 and TT105

PLA                    \ Store the x-delta in QQ19+3 and fetch the current
STA QQ19+3             \ x-coordinate of the crosshairs from QQ10 into A, ready
LDA QQ9                \ for the call to TT123

JSR TT123              \ Call TT123 to move the selected system's galactic
\ x-coordinate by the x-delta, putting the new value in
\ QQ19+4

LDA QQ19+4             \ Store the updated x-coordinate in QQ9 (the current
STA QQ9                \ x-coordinate of the crosshairs)

STA QQ19               \ This instruction has no effect, as QQ19 is overwritten
\ below, both in TT103 and TT105

\ Now we've updated the coordinates of the crosshairs,
\ fall through into TT103 to redraw them at their new
\ location

Type: Subroutine
Category: Charts
Summary: Draw a small set of crosshairs on a chart
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT103
* TT16 calls TT103
* TT23 calls TT103
* hm calls TT103

Draw a small set of crosshairs on a galactic chart at the coordinates in
(QQ9, QQ10).

.TT103

LDA QQ11               \ Fetch the current view type into A

BMI TT105              \ If this is the Short-range Chart screen, jump to TT105

LDA QQ9                \ Store the crosshairs x-coordinate in QQ19
STA QQ19

LDA QQ10               \ Halve the crosshairs y-coordinate and store it in QQ19
LSR A                  \ (we halve it because the Long-range Chart is half as
STA QQ19+1             \ high as it is wide)

LDA #4                 \ Set QQ19+2 to 4 denote crosshairs of size 4
STA QQ19+2

JMP TT15               \ Jump to TT15 to draw crosshairs of size 4 at the
\ crosshairs coordinates, returning from the subroutine
\ using a tail call

Type: Subroutine
Category: Charts
Summary: Move galactic coordinates by a signed delta
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT16 calls TT123
* TT105 calls entry point TT180

Move an 8-bit galactic coordinate by a certain distance in either direction
(i.e. a signed 8-bit delta), but only if it doesn't cause the coordinate to
overflow. The coordinate is in a single axis, so it's either an x-coordinate
or a y-coordinate.

Arguments:

A                    The galactic coordinate to update

QQ19+3               The delta (can be positive or negative)

Returns:

QQ19+4               The updated coordinate after moving by the delta (this
will be the same as A if moving by the delta overflows)

Other entry points:

TT180                Contains an RTS

.TT123

STA QQ19+4             \ Store the original coordinate in temporary storage at
\ QQ19+4

CLC                    \ Set A = A + QQ19+3, so A now contains the original
ADC QQ19+3             \ coordinate, moved by the delta

BMI TT124

BCC TT125              \ If the C flag is clear, then the above addition didn't

RTS                    \ Otherwise the C flag is set and the above addition
\ overflowed, so do not update the return value

.TT124

BCC TT180              \ If the C flag is clear, then because the delta is
\ negative, this indicates the addition (which is
\ TT180 to return from the subroutine without updating
\ the return value

.TT125

STA QQ19+4             \ Store the updated coordinate in QQ19+4

.TT180

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Charts
Summary: Draw crosshairs on the Short-range Chart, with clipping
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT103 calls TT105

Check whether the crosshairs are close enough to the current system to appear
on the Short-range Chart, and if so, draw them.

.TT105

LDA QQ9                \ Set A = QQ9 - QQ0, the horizontal distance between the
SEC                    \ crosshairs (QQ9) and the current system (QQ0)
SBC QQ0

CMP #38                \ If the horizontal distance in A < 38, then the
BCC TT179              \ crosshairs are close enough to the current system to
\ check the vertical distance

CMP #230               \ If the horizontal distance in A < -26, then the
BCC TT180              \ crosshairs are too far from the current system to
\ return from the subroutine (as TT180 contains an RTS)

.TT179

ASL A                  \ Set QQ19 = 104 + A * 4
ASL A                  \
CLC                    \ 104 is the x-coordinate of the centre of the chart,
ADC #104               \ so this sets QQ19 to the screen pixel x-coordinate
STA QQ19               \ of the crosshairs

LDA QQ10               \ Set A = QQ10 - QQ1, the vertical distance between the
SEC                    \ crosshairs (QQ10) and the current system (QQ1)
SBC QQ1

CMP #38                \ If the vertical distance in A is < 38, then the
BCC P%+6               \ crosshairs are close enough to the current system to
\ appear in the Short-range Chart, so skip the next two
\ instructions

CMP #220               \ If the horizontal distance in A is < -36, then the
BCC TT180              \ crosshairs are too far from the current system to
\ return from the subroutine (as TT180 contains an RTS)

ASL A                  \ Set QQ19+1 = 90 + A * 2
CLC                    \
ADC #90                \ 90 is the y-coordinate of the centre of the chart,
STA QQ19+1             \ so this sets QQ19+1 to the screen pixel x-coordinate
\ of the crosshairs

LDA #8                 \ Set QQ19+2 to 8 denote crosshairs of size 8
STA QQ19+2

JMP TT15               \ Jump to TT15 to draw crosshairs of size 8 at the
\ crosshairs coordinates, returning from the subroutine
\ using a tail call

Type: Subroutine
Category: Charts
Summary: Show the Short-range Chart (red key f5)
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT23
* TT114 calls TT23

.TT23

LDA #128               \ Clear the top part of the screen, draw a white border,
JSR TT66               \ and set the current view type in QQ11 to 128 (Short-
\ range Chart)

LDA #7                 \ Move the text cursor to column 7
STA XC

LDA #190               \ Print recursive token 30 ("SHORT RANGE CHART") and
JSR NLIN3              \ draw a horizontal line at pixel row 19 to box in the
\ title

JSR TT14               \ Call TT14 to draw a circle with crosshairs at the
\ current system's galactic coordinates

JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
\ i.e. at the selected system

JSR TT81               \ Set the seeds in QQ15 to those of system 0 in the
\ current galaxy (i.e. copy the seeds from QQ21 to QQ15)

LDA #0                 \ Set A = 0, which we'll use below to zero out the INWK
\ workspace

STA XX20               \ We're about to start working our way through each of
\ the galaxy's systems, so set up a counter in XX20 for
\ each system, starting at 0 and looping through to 255

LDX #24                \ First, though, we need to zero out the 25 bytes at
\ INWK so we can use them to work out which systems have
\ room for a label, so set a counter in X for 25 bytes

.EE3

STA INWK,X             \ Set the X-th byte of INWK to zero

DEX                    \ Decrement the counter

BPL EE3                \ Loop back to EE3 for the next byte until we've zeroed
\ all 25 bytes

\ We now loop through every single system in the galaxy
\ and check the distance from the current system whose
\ coordinates are in (QQ0, QQ1). We get the galactic
\ coordinates of each system from the system's seeds,
\ like this:
\
\   x = s1_hi (which is stored in QQ15+3)
\   y = s0_hi (which is stored in QQ15+1)
\
\ so the following loops through each system in the
\ galaxy in turn and calculates the distance between
\ (QQ0, QQ1) and (s1_hi, s0_hi) to find the closest one

.TT182

LDA QQ15+3             \ Set A = s1_hi - QQ0, the horizontal distance between
SEC                    \ (s1_hi, s0_hi) and (QQ0, QQ1)
SBC QQ0

\ --- Mod: Code added for Elite-A: -------------------->

STA XX12               \ Store the horizontal distance in XX12, so we can
\ retrieve it later

\ --- End of added code ------------------------------->

BCS TT184              \ If a borrow didn't occur, i.e. s1_hi >= QQ0, then the
\ following two instructions

EOR #&FF               \ Otherwise negate the result in A, so A is always
ADC #1                 \ positive (i.e. A = |s1_hi - QQ0|)

.TT184

CMP #20                \ If the horizontal distance in A is >= 20, then this
BCS TT187              \ system is too far away from the current system to
\ move on to the next system

LDA QQ15+1             \ Set A = s0_hi - QQ1, the vertical distance between
SEC                    \ (s1_hi, s0_hi) and (QQ0, QQ1)
SBC QQ1

\ --- Mod: Code added for Elite-A: -------------------->

STA K4                 \ Store the vertical distance in K4, so we can retrieve
\ it later

\ --- End of added code ------------------------------->

BCS TT186              \ If a borrow didn't occur, i.e. s0_hi >= QQ1, then the
\ following two instructions

EOR #&FF               \ Otherwise negate the result in A, so A is always
ADC #1                 \ positive (i.e. A = |s0_hi - QQ1|)

.TT186

CMP #38                \ If the vertical distance in A is >= 38, then this
BCS TT187              \ system is too far away from the current system to
\ move on to the next system

\ This system should be shown on the Short-range Chart,
\ so now we need to work out where the label should go,
\ and set up the various variables we need to draw the
\ system's filled circle on the chart

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA QQ15+3            \ Set A = s1_hi - QQ0, the horizontal distance between
\ SEC                   \ this system and the current system, where |A| < 20.
\ SBC QQ0               \ Let's call this the x-delta, as it's the horizontal
\                       \ difference between the current system at the centre of
\                       \ the chart, and this system (and this time we keep the
\                       \ sign of A, so it can be negative if it's to the left
\                       \ of the chart's centre, or positive if it's to the
\                       \ right)

\ --- And replaced by: -------------------------------->

LDA XX12               \ Retrieve the horizontal distance from XX12, so A now
\ contains the horizontal distance between this system
\ and the current system
\
\ Let's call this the x-delta, as it's the horizontal
\ difference between the current system at the centre of
\ the chart, and this system (so A is negative if it's
\ to the left of the chart's centre, or positive if it's
\ to the right)

\ --- End of replacement ------------------------------>

ASL A                  \ Set XX12 = 104 + x-delta * 4
ASL A                  \
ADC #104               \ 104 is the x-coordinate of the centre of the chart,
STA XX12               \ so this sets XX12 to the centre 104 +/- 76, the pixel
\ x-coordinate of this system

LSR A                  \ Move the text cursor to column x-delta / 2 + 1
LSR A                  \ which will be in the range 1-10
LSR A
STA XC
INC XC

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA QQ15+1            \ Set A = s0_hi - QQ1, the vertical distance between
\ SEC                   \ this system and the current system, where |A| < 38.
\ SBC QQ1               \ Let's call this the y-delta, as it's the vertical
\                       \ difference between the current system at the centre of
\                       \ the chart, and this system (and this time we keep the
\                       \ sign of A, so it can be negative if it's above the
\                       \ chart's centre, or positive if it's below)

\ --- And replaced by: -------------------------------->

LDA K4                 \ Retrieve the vertical distance from XX12, so A now
\ contains the vertical distance between this system
\ and the current system
\
\ Let's call this the y-delta, as it's the vertical
\ difference between the current system at the centre of
\ the chart, and this system (so A is negative if it's
\ above the chart's centre, or positive if it's below)

\ --- End of replacement ------------------------------>

ASL A                  \ Set K4 = 90 + y-delta * 2
STA K4                 \ 90 is the y-coordinate of the centre of the chart,
\ so this sets K4 to the centre 90 +/- 74, the pixel
\ y-coordinate of this system

LSR A                  \ Set Y = K4 / 8, so Y contains the number of the text
LSR A                  \ row that contains this system
LSR A
TAY

\ Now to see if there is room for this system's label.
\ Ideally we would print the system name on the same
\ text row as the system, but we only want to print one
\ label per row, to prevent overlap, so now we check
\ this system's row, and if that's already occupied,
\ the row above, and if that's already occupied, the
\ row below... and if that's already occupied, we give
\ up and don't print a label for this system

LDX INWK,Y             \ If the value in INWK+Y is 0 (i.e. the text row
BEQ EE4                \ containing this system does not already have another
\ system's label on this row

INY                    \ If the value in INWK+Y+1 is 0 (i.e. the text row below
LDX INWK,Y             \ the one containing this system does not already have
BEQ EE4                \ another system's label on it), jump to EE4 to store
\ this system's label on this row

DEY                    \ If the value in INWK+Y-1 is 0 (i.e. the text row above
DEY                    \ the one containing this system does not already have
LDX INWK,Y             \ another system's label on it), fall through into to
BNE ee1                \ EE4 to store this system's label on this row,
\ this system (as there simply isn't room)

.EE4

STY YC                 \ Now to print the label, so move the text cursor to row
\ Y (which contains the row where we can print this
\ system's label)

CPY #3                 \ If Y < 3, then the system would clash with the chart
BCC TT187              \ title, so jump to TT187 to skip showing the system

LDA #&FF               \ Store &FF in INWK+Y, to denote that this row is now
STA INWK,Y             \ occupied so we don't try to print another system's
\ label on this row

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA #%10000000        \ Set bit 7 of QQ17 to switch to Sentence Case
\ STA QQ17

\ --- And replaced by: -------------------------------->

JSR vdu_80             \ Call vdu_80 to switch to Sentence Case

\ --- End of replacement ------------------------------>

JSR cpl                \ Call cpl to print out the system name for the seeds
\ in QQ15 (which now contains the seeds for the current
\ system)

.ee1

LDA #0                 \ Now to plot the star, so set the high bytes of K, K3
STA K3+1               \ and K4 to 0
STA K4+1
STA K+1

LDA XX12               \ Set the low byte of K3 to XX12, the pixel x-coordinate
STA K3                 \ of this system

LDA QQ15+5             \ Fetch s2_hi for this system from QQ15+5, extract bit 0
AND #1                 \ and add 2 to get the size of the star, which we store
ADC #2                 \ in K. This will be either 2, 3 or 4, depending on the
STA K                  \ value of bit 0, and whether the C flag is set (which
\ will vary depending on what happens in the above call
\ to cpl). Incidentally, the planet's average radius
\ also uses s2_hi, bits 0-3 to be precise, but that
\ doesn't mean the two sizes affect each other

\ We now have the following:
\
\   K(1 0)  = radius of star (2, 3 or 4)
\
\   K3(1 0) = pixel x-coordinate of system
\
\   K4(1 0) = pixel y-coordinate of system
\
\ which we can now pass to the SUN routine to draw a
\ small "sun" on the Short-range Chart for this system

JSR FLFLLS             \ Call FLFLLS to reset the LSO block

JSR SUN                \ Call SUN to plot a sun with radius K at pixel
\ coordinate (K3, K4)

JSR FLFLLS             \ Call FLFLLS to reset the LSO block

.TT187

JSR TT20               \ We want to move on to the next system, so call TT20
\ to twist the three 16-bit seeds in QQ15

INC XX20               \ Increment the counter

BEQ TT111-1            \ If X = 0 then we have done all 256 systems, so return
\ from the subroutine (as TT111-1 contains an RTS)

JMP TT182              \ Otherwise jump back up to TT182 to process the next
\ system

Type: Subroutine
Category: Universe
Summary: Set the selected system's seeds to those of system 0
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT111 calls TT81
* TT22 calls TT81
* TT23 calls TT81

Copy the three 16-bit seeds for the current galaxy's system 0 (QQ21) into the
seeds for the selected system (QQ15) - in other words, set the selected
system's seeds to those of system 0.

.TT81

LDX #5                 \ Set up a counter in X to copy six bytes (for three
\ 16-bit numbers)

LDA QQ21,X             \ Copy the X-th byte in QQ21 to the X-th byte in QQ15
STA QQ15,X

DEX                    \ Decrement the counter

BPL TT81+2             \ Loop back up to the LDA instruction if we still have
\ more bytes to copy

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Universe
Summary: Set the current system to the nearest system to a point
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* ESCAPE calls TT111
* Ghy calls TT111
* Main flight loop (Part 3 of 16) calls TT111
* STATUS calls TT111
* TT102 calls TT111
* TT110 calls TT111
* hm calls TT111
* hyp calls TT111
* TT23 calls entry point TT111-1

Given a set of galactic coordinates in (QQ9, QQ10), find the nearest system
to this point in the galaxy, and set this as the currently selected system.

Arguments:

QQ9                  The x-coordinate near which we want to find a system

QQ10                 The y-coordinate near which we want to find a system

Returns:

QQ8(1 0)             The distance from the current system to the nearest
system to the original coordinates

QQ9                  The x-coordinate of the nearest system to the original
coordinates

QQ10                 The y-coordinate of the nearest system to the original
coordinates

QQ15 to QQ15+5       The three 16-bit seeds of the nearest system to the
original coordinates

Other entry points:

TT111-1              Contains an RTS

.TT111

JSR TT81               \ Set the seeds in QQ15 to those of system 0 in the
\ current galaxy (i.e. copy the seeds from QQ21 to QQ15)

\ We now loop through every single system in the galaxy
\ and check the distance from (QQ9, QQ10). We get the
\ galactic coordinates of each system from the system's
\ seeds, like this:
\
\   x = s1_hi (which is stored in QQ15+3)
\   y = s0_hi (which is stored in QQ15+1)
\
\ so the following loops through each system in the
\ galaxy in turn and calculates the distance between
\ (QQ9, QQ10) and (s1_hi, s0_hi) to find the closest one

LDY #127               \ Set Y = T = 127 to hold the shortest distance we've
STY T                  \ found so far, which we initially set to half the
\ distance across the galaxy, or 127, as our coordinate
\ system ranges from (0,0) to (255, 255)

LDA #0                 \ Set A = U = 0 to act as a counter for each system in
STA U                  \ the current galaxy, which we start at system 0 and
\ loop through to 255, the last system

.TT130

LDA QQ15+3             \ Set A = s1_hi - QQ9, the horizontal distance between
SEC                    \ (s1_hi, s0_hi) and (QQ9, QQ10)
SBC QQ9

BCS TT132              \ If a borrow didn't occur, i.e. s1_hi >= QQ9, then the
\ following two instructions

EOR #&FF               \ Otherwise negate the result in A, so A is always
ADC #1                 \ positive (i.e. A = |s1_hi - QQ9|)

.TT132

LSR A                  \ Set S = A / 2
STA S                  \       = |s1_hi - QQ9| / 2

LDA QQ15+1             \ Set A = s0_hi - QQ10, the vertical distance between
SEC                    \ (s1_hi, s0_hi) and (QQ9, QQ10)
SBC QQ10

BCS TT134              \ If a borrow didn't occur, i.e. s0_hi >= QQ10, then the
\ following two instructions

EOR #&FF               \ Otherwise negate the result in A, so A is always
ADC #1                 \ positive (i.e. A = |s0_hi - QQ10|)

.TT134

LSR A                  \ Set A = S + A / 2
CLC                    \       = |s1_hi - QQ9| / 2 + |s0_hi - QQ10| / 2
\ So A now contains the sum of the horizontal and
\ vertical distances, both divided by 2 so the result
\ fits into one byte, and although this doesn't contain
\ the actual distance between the systems, it's a good
\ enough approximation to use for comparing distances

CMP T                  \ If A >= T, then this system's distance is bigger than
BCS TT135              \ our "minimum distance so far" stored in T, so it's no
\ closer than the systems we have already found, so

STA T                  \ This system is the closest to (QQ9, QQ10) so far, so
\ update T with the new "distance" approximation

LDX #5                 \ As this system is the closest we have found yet, we
\ want to store the system's seeds in case it ends up
\ being the closest of all, so we set up a counter in X
\ to copy six bytes (for three 16-bit numbers)

.TT136

LDA QQ15,X             \ Copy the X-th byte in QQ15 to the X-th byte in QQ19,
STA QQ19,X             \ where QQ15 contains the seeds for the system we just
\ found to be the closest so far, and QQ19 is temporary
\ storage

DEX                    \ Decrement the counter

BPL TT136              \ Loop back to TT136 if we still have more bytes to
\ copy

.TT135

JSR TT20               \ We want to move on to the next system, so call TT20
\ to twist the three 16-bit seeds in QQ15

INC U                  \ Increment the system counter in U

BNE TT130              \ If U > 0 then we haven't done all 256 systems yet, so
\ loop back up to TT130

\ We have now finished checking all the systems in the
\ galaxy, and the seeds for the closest system are in
\ QQ19, so now we want to copy these seeds to QQ15,
\ to set the selected system to this closest system

LDX #5                 \ So we set up a counter in X to copy six bytes (for
\ three 16-bit numbers)

.TT137

LDA QQ19,X             \ Copy the X-th byte in QQ19 to the X-th byte in QQ15,
STA QQ15,X

DEX                    \ Decrement the counter

BPL TT137              \ Loop back to TT137 if we still have more bytes to
\ copy

LDA QQ15+1             \ The y-coordinate of the system described by the seeds
STA QQ10               \ in QQ15 is in QQ15+1 (s0_hi), so we copy this to QQ10
\ as this is where we store the selected system's
\ y-coordinate

LDA QQ15+3             \ The x-coordinate of the system described by the seeds
STA QQ9                \ in QQ15 is in QQ15+3 (s1_hi), so we copy this to QQ9
\ as this is where we store the selected system's
\ x-coordinate

\ We have now found the closest system to (QQ9, QQ10)
\ and have set it as the selected system, so now we
\ need to work out the distance between the selected
\ system and the current system

SEC                    \ Set A = QQ9 - QQ0, the horizontal distance between
SBC QQ0                \ the selected system's x-coordinate (QQ9) and the
\ current system's x-coordinate (QQ0)

BCS TT139              \ If a borrow didn't occur, i.e. QQ9 >= QQ0, then the
\ following two instructions

EOR #&FF               \ Otherwise negate the result in A, so A is always
ADC #1                 \ positive (i.e. A = |QQ9 - QQ0|)

\ A now contains the difference between the two
\ systems' x-coordinates, with the sign removed. We
\ will refer to this as the x-delta ("delta" means
\ change or difference in maths)

.TT139

JSR SQUA2              \ Set (A P) = A * A
\           = |QQ9 - QQ0| ^ 2
\           = x_delta ^ 2

STA K+1                \ Store (A P) in K(1 0)
LDA P
STA K

LDA QQ10               \ Set A = QQ10 - QQ1, the vertical distance between the
SEC                    \ selected system's y-coordinate (QQ10) and the current
SBC QQ1                \ system's y-coordinate (QQ1)

BCS TT141              \ If a borrow didn't occur, i.e. QQ10 >= QQ1, then the
\ following two instructions

EOR #&FF               \ Otherwise negate the result in A, so A is always
ADC #1                 \ positive (i.e. A = |QQ10 - QQ1|)

.TT141

LSR A                  \ Set A = A / 2

\ A now contains the difference between the two
\ systems' y-coordinates, with the sign removed, and
\ halved. We halve the value because the galaxy in
\ in Elite is rectangular rather than square, and is
\ twice as wide (x-axis) as it is high (y-axis), so to
\ get a distance that matches the shape of the
\ long-range galaxy chart, we need to halve the
\ distance between the vertical y-coordinates. We will
\ refer to this as the y-delta

JSR SQUA2              \ Set (A P) = A * A
\           = (|QQ10 - QQ1| / 2) ^ 2
\           = y_delta ^ 2

\ By this point we have the following results:
\
\   K(1 0) = x_delta ^ 2
\    (A P) = y_delta ^ 2
\
\ so to find the distance between the two points, we
\ can use Pythagoras - so first we need to add the two
\ results together, and then take the square root

PHA                    \ Store the high byte of the y-axis value on the stack,
\ so we can use A for another purpose

LDA P                  \ Set Q = P + K, which adds the low bytes of the two
CLC                    \ calculated values
STA Q

PLA                    \ Restore the high byte of the y-axis value from the
\ stack into A again

ADC K+1                \ Set R = A + K+1, which adds the high bytes of the two
STA R                  \ calculated values, so we now have:
\
\   (R Q) = K(1 0) + (A P)
\         = (x_delta ^ 2) + (y_delta ^ 2)

JSR LL5                \ Set Q = SQRT(R Q), so Q now contains the distance
\ between the two systems, in terms of coordinates

\ We now store the distance to the selected system * 4
\ in the two-byte location QQ8, by taking (0 Q) and
\ shifting it left twice, storing it in QQ8(1 0)

LDA Q                  \ First we shift the low byte left by setting
ASL A                  \ A = Q * 2, with bit 7 of A going into the C flag

LDX #0                 \ Now we set the high byte in QQ8+1 to 0 and rotate
STX QQ8+1              \ the C flag into bit 0 of QQ8+1
ROL QQ8+1

ASL A                  \ And then we repeat the shift left of (QQ8+1 A)
ROL QQ8+1

STA QQ8                \ And store A in the low byte, QQ8, so QQ8(1 0) now
\ contains Q * 4. Given that the width of the galaxy is
\ 256 in coordinate terms, the width of the galaxy
\ would be 1024 in the units we store in QQ8

JMP TT24               \ Call TT24 to calculate system data from the seeds in
\ QQ15 and store them in the relevant locations, so our
\ new selected system is fully set up, and return from
\ the subroutine using a tail call

Type: Subroutine
Category: Flight
Summary: Start the hyperspace process
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls hyp

Called when "H" or CTRL-H is pressed during flight. Checks the following:

* We are in space

* We are not already in a hyperspace countdown

If CTRL is being held down, we jump to Ghy to engage the galactic hyperdrive,
otherwise we check that:

* The selected system is not the current system

* We have enough fuel to make the jump

and if all the pre-jump checks are passed, we print the destination on-screen
and start the countdown.

Other entry points:

TTX111               Used to rejoin this routine from the call to TTX110

.hyp

LDA QQ22+1             \ Fetch QQ22+1, which contains the number that's shown
\ on-screen during hyperspace countdown

ORA QQ12               \ If we are docked (QQ12 = &FF) or there is already a
BNE zZ+1               \ countdown in progress, then return from the subroutine
\ using a tail call (as zZ+1 contains an RTS), as we
\ can't hyperspace when docked, or there is already a
\ countdown in progress

JSR CTRL               \ Scan the keyboard to see if CTRL is currently pressed

BMI Ghy                \ If it is, then the galactic hyperdrive has been

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA QQ11              \ If the current view is 0 (i.e. the space view) then
\ BNE P%+5              \ jump to TTX110, which calls TT111 to set the current
\ JMP TTX110            \ system to the nearest system to (QQ9, QQ10), and jumps
\                       \ back into this routine at TTX111 below

\ --- And replaced by: -------------------------------->

LDA QQ11               \ If the current view is not 0 (i.e. not the space view)
BNE P%+8               \ then skip the following two instructions

JSR TT111              \ This is the space view, so select the system closest
\ to galactic coordinates (QQ9, QQ10)

JMP TTX111             \ Skip the following instruction, as we don't want to
\ draw the crosshairs in the space view

\ --- End of replacement ------------------------------>

JSR hm                 \ This is a chart view, so call hm to redraw the chart
\ crosshairs

.TTX111

\ If we get here then the current view is either the
\ space view or a chart

LDA QQ8                \ If both bytes of the distance to the selected system
ORA QQ8+1              \ in QQ8 are zero, return from the subroutine (as zZ+1
BEQ zZ+1               \ contains an RTS), as the selected system is the
\ current system

LDA #7                 \ Move the text cursor to column 7, row 23 (in the
STA XC                 \ middle of the bottom text row)
LDA #23
STA YC

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA #0                \ Set QQ17 = 0 to switch to ALL CAPS
\ STA QQ17

\ --- And replaced by: -------------------------------->

JSR vdu_00             \ Call vdu_00 to switch to ALL CAPS

\ --- End of replacement ------------------------------>

LDA #189               \ Print recursive token 29 ("HYPERSPACE ")
JSR TT27

LDA QQ8+1              \ If the high byte of the distance to the selected
BNE TT147              \ system in QQ8 is > 0, then it is definitely too far to
\ jump (as our maximum range is 7.0 light years, or a
\ value of 70 in QQ8(1 0)), so jump to TT147 to print
\ "RANGE?" and return from the subroutine using a tail
\ call

LDA QQ14               \ Fetch our current fuel level from Q114 into A

CMP QQ8                \ If our fuel reserves are less than the distance to the
BCC TT147              \ selected system, then we don't have enough fuel for
\ return from the subroutine using a tail call

LDA #'-'               \ Print a hyphen
JSR TT27

JSR cpl                \ Call cpl to print the name of the selected system

\ Fall through into wW to start the hyperspace countdown

Type: Subroutine
Category: Flight
Summary: Start a hyperspace countdown
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* Ghy calls wW

Start the hyperspace countdown (for both inter-system hyperspace and the
galactic hyperdrive).

.wW

LDA #15                \ The hyperspace countdown starts from 15, so set A to
\ to 15 so we can set the two hyperspace counters

STA QQ22+1             \ Set the number in QQ22+1 to 15, which is the number
\ that's shown on-screen during the hyperspace countdown

STA QQ22               \ Set the number in QQ22 to 15, which is the internal
\ counter that counts down by 1 each iteration of the
\ main game loop, and each time it reaches zero, the
\ on-screen counter gets decremented, and QQ22 gets set
\ to 5, so setting QQ22 to 15 here makes the first tick
\ of the hyperspace counter longer than subsequent ticks

\ --- Mod: Original Acornsoft code removed: ----------->

\ TAX                   \ Print the 8-bit number in X (i.e. 15) at text location
\ JMP ee3               \ (0, 1), padded to 5 digits, so it appears in the top
\                       \ left corner of the screen, and return from the
\                       \ subroutine using a tail call

\ --- And replaced by: -------------------------------->

TAX                    \ Print the 8-bit number in X (i.e. 15) at text location
BNE ee3                \ (0, 1), padded to 5 digits, so it appears in the top
\ left corner of the screen, and return from the
\ subroutine using a tail call (the BNE is effectively a
\ JMP as A is never zero)

\ --- End of replacement ------------------------------>

Type: Subroutine
Category: Flight
Summary: Perform a galactic hyperspace jump
Deep dive: Twisting the system seeds
Galaxy and system seeds
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* hyp calls Ghy
* hyp calls entry point zZ+1

Engage the galactic hyperdrive. Called from the hyp routine above if CTRL-H is
being pressed.

This routine also updates the galaxy seeds to point to the next galaxy. Using
a galactic hyperdrive rotates each seed byte to the left, rolling each byte
left within itself like this:

01234567 -> 12345670

to get the seeds for the next galaxy. So after 8 galactic jumps, the seeds
roll round to those of the first galaxy again.

We always arrive in a new galaxy at galactic coordinates (96, 96), and then
find the nearest system and set that as our location.

Other entry points:

zZ+1                 Contains an RTS

.Ghy

LDX GHYP               \ Fetch GHYP, which tells us whether we own a galactic
BEQ zZ+1               \ hyperdrive, and if it is zero, which means we don't,
\ return from the subroutine (as zZ+1 contains an RTS)

\ --- Mod: Code added for Elite-A: -------------------->

INC new_hold           \ Free up one tonne of space in the hold, as we have
\ just used up the galactic hyperdrive

\ --- End of added code ------------------------------->

INX                    \ We own a galactic hyperdrive, so X is &FF, so this
\ instruction sets X = 0

STX GHYP               \ The galactic hyperdrive is a one-use item, so set GHYP
\ to 0 so we no longer have one fitted

STX FIST               \ Changing galaxy also clears our criminal record, so
\ set our legal status in FIST to 0 ("clean")

\ --- Mod: Code added for Elite-A: -------------------->

STX cmdr_cour          \ Reset the special cargo delivery mission timer in
STX cmdr_cour+1        \ cmdr_cour(1 0)

\ --- End of added code ------------------------------->

JSR wW                 \ Call wW to start the hyperspace countdown

LDX #5                 \ To move galaxy, we rotate the galaxy's seeds left, so
\ set a counter in X for the 6 seed bytes

INC GCNT               \ Increment the current galaxy number in GCNT

LDA GCNT               \ Set GCNT = GCNT mod 8, so we jump from galaxy 7 back
AND #7                 \ to galaxy 0 (shown in-game as going from galaxy 8 back
STA GCNT               \ to the starting point in galaxy 1)

.G1

LDA QQ21,X             \ Load the X-th seed byte into A

ASL A                  \ Set the C flag to bit 7 of the seed

ROL QQ21,X             \ Rotate the seed in memory, which will add bit 7 back
\ in as bit 0, so this rolls the seed around on itself

DEX                    \ Decrement the counter

BPL G1                 \ Loop back for the next seed byte, until we have
\ rotated them all

.zZ

LDA #96                \ Set (QQ9, QQ10) to (96, 96), which is where we always
STA QQ9                \ arrive in a new galaxy (the selected system will be
STA QQ10               \ set to the nearest actual system later on)

JSR TT110              \ Call TT110 to show the front space view

JSR TT111              \ Call TT111 to set the current system to the nearest
\ system to (QQ9, QQ10), and put the seeds of the
\ nearest system into QQ15 to QQ15+5
\
\ This call fixes a bug in the cassette version, where
\ the galactic hyperdrive will take us to coordinates
\ (96, 96) in the new galaxy, even if there isn't
\ actually a system there, so if we jump when we are
\ low on fuel, it is possible to get stuck in the
\ middle of nowhere when changing galaxy
\
\ This call sets the current system correctly, so we
\ always arrive at the nearest system to (96, 96)

LDX #0                 \ Set the distance to the selected system in QQ8(1 0)
STX QQ8                \ to 0
STX QQ8+1

LDA #116               \ Print recursive token 116 (GALACTIC HYPERSPACE ")
JSR MESS               \ as an in-flight message

\ Fall through into jmp to set the system to the
\ current system and return from the subroutine there

Type: Subroutine
Category: Universe
Summary: Set the current system to the selected system
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* ESCAPE calls jmp
* hyp1 calls jmp

Returns:

(QQ0, QQ1)           The galactic coordinates of the new system

Other entry points:

hy5                  Contains an RTS

.jmp

LDA QQ9                \ Set the current system's galactic x-coordinate to the
STA QQ0                \ x-coordinate of the selected system

LDA QQ10               \ Set the current system's galactic y-coordinate to the
STA QQ1                \ y-coordinate of the selected system

.hy5

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Text
Summary: Print the hyperspace countdown in the top-left of the screen
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls ee3
* TTX66 calls ee3
* wW calls ee3

Print the 8-bit number in X at text location (1, 1). Print the number to
5 digits, left-padding with spaces for numbers with fewer than 3 digits (so
numbers < 10000 are right-aligned), with no decimal point.

Arguments:

X                    The number to print

.ee3

LDY #1                 \ Move the text cursor to column 1
STY XC

STY YC                 \ Move the text cursor to row 1

DEY                    \ Decrement Y to 0 for the high byte in pr6

\ Fall through into pr6 to print X to 5 digits, as the
\ high byte in Y is 0

Type: Subroutine
Category: Text
Summary: Print 16-bit number, left-padded to 5 digits, no point
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT25 calls pr6

Print the 16-bit number in (Y X) to 5 digits, left-padding with spaces for
numbers with fewer than 3 digits (so numbers < 10000 are right-aligned),
with no decimal point.

Arguments:

X                    The low byte of the number to print

Y                    The high byte of the number to print

.pr6

CLC                    \ Do not display a decimal point when printing

\ Fall through into pr5 to print X to 5 digits

Type: Subroutine
Category: Text
Summary: Print a 16-bit number, left-padded to 5 digits, and optional point
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT146 calls pr5
* TT151 calls pr5
* TT25 calls pr5

Print the 16-bit number in (Y X) to 5 digits, left-padding with spaces for
numbers with fewer than 3 digits (so numbers < 10000 are right-aligned).
Optionally include a decimal point.

Arguments:

X                    The low byte of the number to print

Y                    The high byte of the number to print

C flag               If set, include a decimal point

.pr5

LDA #5                 \ Set the number of digits to print to 5

JMP TT11               \ Call TT11 to print (Y X) to 5 digits and return from
\ the subroutine using a tail call

Type: Subroutine
Category: Text
Summary: Print an error when a system is out of hyperspace range
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* hyp calls TT147

Print "RANGE?" for when the hyperspace distance is too far

.TT147

LDA #202               \ Load A with token 42 ("RANGE") and fall through into
\ prq to print it, followed by a question mark

Type: Subroutine
Category: Text
Summary: Print a text token followed by a question mark
Context: See this subroutine on its own page
References: No direct references to this subroutine in this source file

Arguments:

A                    The text token to be printed

.prq

JSR TT27               \ Print the text token in A

LDA #'?'               \ Print a question mark and return from the
JMP TT27               \ subroutine using a tail call

Type: Subroutine
Category: Flight
Summary: Set the current system to the nearest system and return to hyp
Context: See this subroutine on its own page
References: No direct references to this subroutine in this source file

\ --- Mod: Original Acornsoft code removed: ----------->

\.TTX110

\                       \ This routine is only called from the hyp routine, and
\                       \ it jumps back into hyp at label TTX111

\ JSR TT111             \ Call TT111 to set the current system to the nearest
\                       \ system to (QQ9, QQ10), and put the seeds of the
\                       \ nearest system into QQ15 to QQ15+5

\ --- End of removed code ----------------------------->

Type: Subroutine
Category: Market
Summary: Print the name, price and availability of a market item
Deep dive: Market item prices and availability
Galaxy and system seeds
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT167 calls TT151

Arguments:

A                    The number of the market item to print, 0-16 (see QQ23
for details of item numbers)

Returns:

QQ19+1               Byte #1 from the market prices table for this item

QQ24                 The item's price / 4

QQ25                 The item's availability

.TT151

PHA                    \ Store the item number on the stack and in QQ14+4
STA QQ19+4

ASL A                  \ Store the item number * 4 in QQ19, so this will act as
ASL A                  \ an index into the market prices table at QQ23 for this
STA QQ19               \ item (as there are four bytes per item in the table)

LDA #1                 \ Move the text cursor to column 1, for the item's name
STA XC

PLA                    \ Restore the item number

ADC #208               \ Print recursive token 48 + A, which will be in the
JSR TT27               \ range 48 ("FOOD") to 64 ("ALIEN ITEMS"), so this
\ prints the item's name

LDA #14                \ Move the text cursor to column 14, for the price
STA XC

LDX QQ19               \ Fetch byte #1 from the market prices table (units and
LDA QQ23+1,X           \ economic_factor) for this item and store in QQ19+1
STA QQ19+1

LDA QQ26               \ Fetch the random number for this system visit and
AND QQ23+3,X           \ AND with byte #3 from the market prices table (mask)
\ to give:
\
\   A = random AND mask

CLC                    \ Add byte #0 from the market prices table (base_price),
ADC QQ23,X             \ so we now have:
STA QQ24               \
\   A = base_price + (random AND mask)

JSR TT152              \ Call TT152 to print the item's unit ("t", "kg" or
\ "g"), padded to a width of two characters

JSR var                \ Call var to set QQ19+3 = economy * |economic_factor|
\ (and set the availability of alien items to 0)

LDA QQ19+1             \ Fetch the byte #1 that we stored above and jump to
BMI TT155              \ TT155 if it is negative (i.e. if the economic_factor
\ is negative)

LDA QQ24               \ Set A = QQ24 + QQ19+3
\       = base_price + (random AND mask)
\         + (economy * |economic_factor|)
\
\ which is the result we want, as the economic_factor
\ is positive

JMP TT156              \ Jump to TT156 to multiply the result by 4

.TT155

LDA QQ24               \ Set A = QQ24 - QQ19+3
SEC                    \
SBC QQ19+3             \       = base_price + (random AND mask)
\         - (economy * |economic_factor|)
\
\ which is the result we want, as economic_factor
\ is negative

.TT156

STA QQ24               \ Store the result in QQ24 and P
STA P

LDA #0                 \ Set A = 0 and call GC2 to calculate (Y X) = (A P) * 4,
JSR GC2                \ which is the same as (Y X) = P * 4 because A = 0

SEC                    \ We now have our final price, * 10, so we can call pr5
JSR pr5                \ to print (Y X) to 5 digits, including a decimal
\ point, as the C flag is set

LDY QQ19+4             \ We now move on to availability, so fetch the market
\ item number that we stored in QQ19+4 at the start

LDA #5                 \ Set A to 5 so we can print the availability to 5

LDX AVL,Y              \ Set X to the item's availability, which is given in
\ the AVL table

STX QQ25               \ Store the availability in QQ25

CLC                    \ Clear the C flag

BEQ TT172              \ If none are available, jump to TT172 to print a tab
\ and a "-"

JSR pr2+2              \ Otherwise print the 8-bit number in X to 5 digits,
\ right-aligned with spaces. This works because we set
\ A to 5 above, and we jump into the pr2 routine just
\ after the first instruction, which would normally
\ set the number of digits to 3

JMP TT152              \ Print the unit ("t", "kg" or "g") for the market item,
\ with a following space if required to make it two
\ characters long

.TT172

LDA XC                 \ Move the text cursor in XC to the right by 4 columns,
ADC #4                 \ so the cursor is where the last digit would be if we
STA XC                 \ were printing a 5-digit availability number

LDA #'-'               \ Print a "-" character by jumping to TT162+2, which
BNE TT162+2            \ contains JMP TT27 (this BNE is effectively a JMP as A
\ will never be zero), and return from the subroutine
\ using a tail call

Type: Subroutine
Category: Market
Summary: Print the unit ("t", "kg" or "g") for a market item
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT151 calls TT152
* TT210 calls TT152

Print the unit ("t", "kg" or "g") for the market item whose byte #1 from the
market prices table is in QQ19+1, right-padded with spaces to a width of two
characters (so that's "t ", "kg" or "g ").

.TT152

LDA QQ19+1             \ Fetch the economic_factor from QQ19+1

AND #96                \ If bits 5 and 6 are both clear, jump to TT160 to
BEQ TT160              \ print "t" for tonne, followed by a space, and return
\ from the subroutine using a tail call

CMP #32                \ If bit 5 is set, jump to TT161 to print "kg" for
BEQ TT161              \ kilograms, and return from the subroutine using a tail
\ call

JSR TT16a              \ Otherwise call TT16a to print "g" for grams, and fall
\ through into TT162 to print a space and return from
\ the subroutine

Type: Subroutine
Category: Text
Summary: Print a space

Other entry points:

Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT160 calls TT162
* TT25 calls TT162
* TTX66 calls TT162
* spc calls TT162
* TT151 calls entry point TT162+2
* TT163 calls entry point TT162+2

.TT162

LDA #' '               \ Load a space character into A

JMP TT27               \ Print the text token in A and return from the
\ subroutine using a tail call

Type: Subroutine
Category: Market
Summary: Print "t" (for tonne) and a space
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT152 calls TT160
* TT213 calls TT160

.TT160

LDA #'t'               \ Load a "t" character into A

JSR TT26               \ Print the character, using TT216 so that it doesn't
\ change the character case

BCC TT162              \ Jump to TT162 to print a space and return from the
\ subroutine using a tail call (this BCC is effectively
\ a JMP as the C flag is cleared by TT26)

Type: Subroutine
Category: Market
Summary: Print "kg" (for kilograms)
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT152 calls TT161

.TT161

LDA #'k'               \ Load a "k" character into A

JSR TT26               \ Print the character, using TT216 so that it doesn't
\ change the character case, and fall through into
\ TT16a to print a "g" character

Type: Subroutine
Category: Market
Summary: Print "g" (for grams)
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT152 calls TT16a

.TT16a

LDA #'g'               \ Load a "g" character into A

JMP TT26               \ Print the character, using TT216 so that it doesn't
\ change the character case, and return from the
\ subroutine using a tail call

Type: Subroutine
Category: Market
Summary: Print the headers for the table of market prices
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT167 calls TT163

Print the column headers for the prices table in the Buy Cargo and Market
Price screens.

.TT163

LDA #17                \ Move the text cursor in XC to column 17
STA XC

LDA #255               \ Print recursive token 95 token ("UNIT  QUANTITY
BNE TT162+2            \ {crlf} PRODUCT   UNIT PRICE FOR SALE{crlf}{lf}") by
\ jumping to TT162+2, which contains JMP TT27 (this BNE
\ is effectively a JMP as A will never be zero), and
\ return from the subroutine using a tail call

Type: Subroutine
Category: Market
Summary: Show the Market Price screen (red key f7)
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT167

.TT167

LDA #16                \ Clear the top part of the screen, draw a white border,
JSR TT66               \ and set the current view type in QQ11 to 16 (Market
\ Price screen)

LDA #5                 \ Move the text cursor to column 4
STA XC

LDA #167               \ Print recursive token 7 ("{current system name} MARKET
JSR NLIN3              \ PRICES") and draw a horizontal line at pixel row 19
\ to box in the title

LDA #3                 \ Move the text cursor to row 3
STA YC

JSR TT163              \ Print the column headers for the prices table

LDA #0                 \ We're going to loop through all the available market
STA QQ29               \ items, so we set up a counter in QQ29 to denote the
\ current item and start it at 0

.TT168

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDX #%10000000        \ Set bit 7 of QQ17 to switch to Sentence Case, with the
\ STX QQ17              \ next letter in capitals

\ --- And replaced by: -------------------------------->

JSR vdu_80             \ Call vdu_80 to switch to Sentence Case, with the next
\ letter in capitals

\ --- End of replacement ------------------------------>

JSR TT151              \ Call TT151 to print the item name, market price and
\ availability of the current item, and set QQ24 to the
\ item's price / 4, QQ25 to the quantity available and
\ QQ19+1 to byte #1 from the market prices table for
\ this item

INC YC                 \ Move the text cursor down one row

INC QQ29               \ Increment QQ29 to point to the next item

LDA QQ29               \ If QQ29 >= 17 then jump to TT168 as we have done the
CMP #17                \ last item
BCC TT168

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Market
Summary: Calculate QQ19+3 = economy * |economic_factor|
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* GVL calls var
* TT151 calls var

Set QQ19+3 = economy * |economic_factor|, given byte #1 of the market prices
table for an item. Also sets the availability of alien items to 0.

This routine forms part of the calculations for market item prices (TT151)
and availability (GVL).

Arguments:

QQ19+1               Byte #1 of the market prices table for this market item
(which contains the economic_factor in bits 0-5, and the
sign of the economic_factor in bit 7)

.var

LDA QQ19+1             \ Extract bits 0-5 from QQ19+1 into A, to get the
AND #31                \ economic_factor without its sign, in other words:
\
\   A = |economic_factor|

LDY QQ28               \ Set Y to the economy byte of the current system

STA QQ19+2             \ Store A in QQ19+2

CLC                    \ Clear the C flag so we can do additions below

LDA #0                 \ Set AVL+16 (availability of alien items) to 0,
STA AVL+16             \ setting A to 0 in the process

.TT153

\ We now do the multiplication by doing a series of
\ additions in a loop, building the result in A. Each
\ loop adds QQ19+2 (|economic_factor|) to A, and it
\ loops the number of times given by the economy byte;
\ in other words, because A starts at 0, this sets:
\
\   A = economy * |economic_factor|

DEY                    \ Decrement the economy in Y, exiting the loop when it
BMI TT154              \ becomes negative

JMP TT153              \ Loop back to TT153 to do another addition

.TT154

STA QQ19+3             \ Store the result in QQ19+3

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Universe
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT18 calls hyp1

(QQ9, QQ10), and set up the current system's state to those of the new system.

Returns:

(QQ0, QQ1)           The galactic coordinates of the new system

QQ2 to QQ2+6         The seeds of the new system

EV                   Set to 0

QQ28                 The new system's economy

tek                  The new system's tech level

gov                  The new system's government

Other entry points:

hyp1+3               Jump straight to the system at (QQ9, QQ10) without
first calculating which system is closest. We do this
if we already know that (QQ9, QQ10) points to a system

.hyp1

\ --- Mod: Original Acornsoft code removed: ----------->

\ JSR TT111             \ Select the system closest to galactic coordinates
\                       \ (QQ9, QQ10)

\ --- End of removed code ----------------------------->

JSR jmp                \ Set the current system to the selected system

LDX #5                 \ We now want to copy the seeds for the selected system
\ in QQ15 into QQ2, where we store the seeds for the
\ current system, so set up a counter in X for copying
\ 6 bytes (for three 16-bit seeds)

.TT112

LDA QQ15,X             \ Copy the X-th byte in QQ15 to the X-th byte in QQ2, to
STA QQ2,X              \ update the selected system to the new one. Note that
\ this approach has a minor bug associated with it: if
\ your hyperspace counter hits 0 just as you're docking,
\ then you will magically appear in the station in your
\ hyperspace destination, without having to go to the
\ effort of actually flying there. This bug was fixed in
\ later versions by saving the destination seeds in a
\ separate location called safehouse, and using those
\ instead... but that isn't the case in this version

DEX                    \ Decrement the counter

BPL TT112              \ Loop back to TT112 if we still have more bytes to
\ copy

INX                    \ Set X = 0 (as we ended the above loop with X = &FF)

STX EV                 \ Set EV, the extra vessels spawning counter, to 0, as
\ we are entering a new system with no extra vessels
\ spawned

LDA QQ3                \ Set the current system's economy in QQ28 to the
STA QQ28               \ selected system's economy from QQ3

LDA QQ5                \ Set the current system's tech level in tek to the
STA tek                \ selected system's economy from QQ5

LDA QQ4                \ Set the current system's government in gov to the
STA gov                \ selected system's government from QQ4

\ Fall through into GVL to calculate the availability of
\ market items in the new system

Type: Subroutine
Category: Universe
Summary: Calculate the availability of market items
Deep dive: Market item prices and availability
Galaxy and system seeds
Context: See this subroutine on its own page
References: No direct references to this subroutine in this source file

Calculate the availability for each market item and store it in AVL. This is
called on arrival in a new system.

Other entry points:

hyR                  Contains an RTS

.GVL

JSR DORND              \ Set A and X to random numbers

STA QQ26               \ Set QQ26 to the random byte that's used in the market
\ calculations

LDX #0                 \ We are now going to loop through the market item
STX XX4                \ availability table in AVL, so set a counter in XX4
\ (and X) for the market item number, starting with 0

.hy9

LDA QQ23+1,X           \ Fetch byte #1 from the market prices table (units and
STA QQ19+1             \ economic_factor) for item number X and store it in
\ QQ19+1

JSR var                \ Call var to set QQ19+3 = economy * |economic_factor|
\ (and set the availability of alien items to 0)

LDA QQ23+3,X           \ Fetch byte #3 from the market prices table (mask) and
AND QQ26               \ AND with the random number for this system visit
\ to give:
\
\   A = random AND mask

CLC                    \ Add byte #2 from the market prices table
ADC QQ23+2,X           \ (base_quantity) so we now have:
\
\   A = base_quantity + (random AND mask)

LDY QQ19+1             \ Fetch the byte #1 that we stored above and jump to
BMI TT157              \ TT157 if it is negative (i.e. if the economic_factor
\ is negative)

SEC                    \ Set A = A - QQ19+3
SBC QQ19+3             \
\       = base_quantity + (random AND mask)
\         - (economy * |economic_factor|)
\
\ which is the result we want, as the economic_factor
\ is positive

.TT157

CLC                    \ Set A = A + QQ19+3
\       = base_quantity + (random AND mask)
\         + (economy * |economic_factor|)
\
\ which is the result we want, as the economic_factor
\ is negative

.TT158

BPL TT159              \ If A < 0, then set A = 0, so we don't have negative
LDA #0                 \ availability

.TT159

LDY XX4                \ Fetch the counter (the market item number) into Y

AND #%00111111         \ Take bits 0-5 of A, i.e. A mod 64, and store this as
STA AVL,Y              \ this item's availability in the Y=th byte of AVL, so
\ each item has a maximum availability of 63t

INY                    \ Increment the counter into XX44, Y and A
TYA
STA XX4

ASL A                  \ Set X = counter * 4, so that X points to the next
ASL A                  \ item's entry in the four-byte market prices table,
TAX                    \ ready for the next loop

CMP #63                \ If A < 63, jump back up to hy9 to set the availability
BCC hy9                \ for the next market item

.hyR

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Universe
Summary: Spawn a Thargoid ship and a Thargon companion
Deep dive: Fixing ship positions
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* MJP calls GTHG
* Main game loop (Part 4 of 6) calls GTHG

.GTHG

JSR Ze                 \ Call Ze to initialise INWK
\
\ Note that because Ze uses the value of X returned by
\ DORND, and X contains the value of A returned by the
\ previous call to DORND, this does not set the new ship
\ to a totally random location. See the deep dive on
\ "Fixing ship positions" for details

LDA #%11111111         \ Set the AI flag in byte #32 so that the ship has AI,
STA INWK+32            \ is extremely and aggressively hostile, and has E.C.M.

LDA #THG               \ Call NWSHP to add a new Thargoid ship to our local
JSR NWSHP              \ bubble of universe

LDA #TGL               \ Call NWSHP to add a new Thargon ship to our local
JMP NWSHP              \ bubble of universe, and return from the subroutine
\ using a tail call

Type: Subroutine
Category: Flight
Summary: Process a mis-jump into witchspace
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT18 calls MJP
* TT18 calls entry point RTS111

Process a mis-jump into witchspace (which happens very rarely). Witchspace has
a strange, almost dust-free aspect to it, and it is populated by hostile
Thargoids. Using our escape pod will be fatal, and our position on the
galactic chart is in-between systems. It is a scary place...

There is a 1% chance that this routine is called from TT18 instead of doing
a normal hyperspace, or we can manually trigger a mis-jump by holding down
CTRL after first enabling the "author display" configuration option ("X") when
paused.

Other entry points:

RTS111               Contains an RTS

\ --- Mod: Original Acornsoft code removed: ----------->

\.ptg

\ LSR COK               \ Set bit 0 of the competition flags in COK, so that the
\ SEC                   \ copmpetition code will include the fact that we have
\ ROL COK               \ manually forced a mis-jump into witchspace

\ --- End of removed code ----------------------------->

.MJP

LDA #3                 \ Call SHIPinA to load ship blueprints file D, which is
JSR SHIPinA            \ one of the two files that contain Thargoids

LDA #3                 \ Clear the top part of the screen, draw a white border,
JSR TT66               \ and set the current view type in QQ11 to 3

JSR LL164              \ Call LL164 to show the hyperspace tunnel and make the
\ hyperspace sound for a second time (as we already
\ called LL164 in TT18)

JSR RES2               \ Reset a number of flight variables and workspaces, as
\ well as setting Y to &FF

STY MJ                 \ Set the mis-jump flag in MJ to &FF, to indicate that
\ we are now in witchspace

.MJP1

JSR GTHG               \ Call GTHG to spawn a Thargoid ship

LDA #3                 \ Fetch the number of Thargoid ships from MANY+THG, and
CMP MANY+THG           \ if it is less than or equal to 3, loop back to MJP1 to
BCS MJP1               \ spawn another one, until we have four Thargoids

STA NOSTM              \ Set NOSTM (the maximum number of stardust particles)
\ to 3, so there are fewer bits of stardust in
\ witchspace (normal space has a maximum of 18)

LDX #0                 \ Initialise the front space view
JSR LOOK1

LDA QQ1                \ Fetch the current system's galactic y-coordinate in
EOR #%00011111         \ QQ1 and flip bits 0-5, so we end up somewhere in the
STA QQ1                \ vicinity of our original destination, but above or
\ below it in the galactic chart

\ --- Mod: Code added for Elite-A: -------------------->

.RTS111

\ --- End of added code ------------------------------->

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Flight
Summary: Try to initiate a jump into hyperspace
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls TT18
* Main flight loop (Part 3 of 16) calls entry point hyper_snap

Try to go through hyperspace. Called from TT102 in the main loop when the
hyperspace countdown has finished.

Other entry points:

hyper_snap           Perform a hyperspace, but without using up any fuel

.TT18

LDA QQ14               \ Subtract the distance to the selected system (in QQ8)
SEC                    \ from the amount of fuel in our tank (in QQ14) into A
SBC QQ8

STA QQ14               \ Store the updated fuel amount in QQ14

\ --- Mod: Code added for Elite-A: -------------------->

.hyper_snap

\ --- End of added code ------------------------------->

LDA QQ11               \ If the current view is not a space view, jump to ee5
BNE ee5                \ to skip the following

JSR TT66               \ Clear the top part of the screen, draw a white border,
\ and set the current view type in QQ11 to 0 (space
\ view)

JSR LL164              \ Call LL164 to show the hyperspace tunnel and make the
\ hyperspace sound

.ee5

\ --- Mod: Original Acornsoft code removed: ----------->

\ JSR CTRL              \ Scan the keyboard to see if CTRL is currently pressed,
\                       \ returning a negative value in A if it is

\ AND PATG              \ If the game is configured to show the author's names
\                       \ on the start-up screen, then PATG will contain &FF,
\                       \ otherwise it will be 0

\ BMI ptg               \ By now, A will be negative if we are holding down CTRL
\                       \ and author names are configured, which is what we have
\                       \ to do in order to trigger a manual mis-jump, so jump
\                       \ to ptg to do a mis-jump (ptg not only mis-jumps, but
\                       \ updates the competition flags, so Acornsoft could tell
\                       \ from the competition code whether this feature had
\                       \ been used)

\ JSR DORND             \ Set A and X to random numbers

\ CMP #253              \ If A >= 253 (1% chance) then jump to MJP to trigger a
\ BCS MJP               \ mis-jump into witchspace

\ JSR hyp1+3            \ Jump straight to the system at (QQ9, QQ10) without
\                       \ first calculating which system is closest

\ --- And replaced by: -------------------------------->

JSR DORND              \ Set A and X to random numbers

CMP #253               \ If A >= 253 (1% chance) then jump to MJP to trigger a
BCS MJP                \ mis-jump into witchspace

JSR hyp1               \ Jump straight to the system at (QQ9, QQ10)

\ --- End of replacement ------------------------------>

JSR RES2               \ Reset a number of flight variables and workspaces

JSR SOLAR              \ Halve our legal status, update the missile indicators,
\ and set up data blocks and slots for the planet and
\ sun

JSR LSHIPS             \ Call LSHIPS to load a new ship blueprints file

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA QQ11              \ If the current view in QQ11 is not a space view (0) or
\ AND #%00111111        \ one of the charts (64 or 128), return from the
\ BNE TT113             \ subroutine (as TT113 contains an RTS)

\ --- And replaced by: -------------------------------->

LDA QQ11               \ If the current view in QQ11 is not a space view (0) or
AND #%00111111         \ one of the charts (64 or 128), return from the
BNE RTS111             \ subroutine (as RTS111 contains an RTS)

\ --- End of replacement ------------------------------>

JSR TTX66              \ Otherwise clear the screen and draw a white border

LDA QQ11               \ If the current view is one of the charts, jump to
BNE TT114              \ TT114 (from which we jump to the correct routine to
\ display the chart)

INC QQ11               \ This is a space view, so increment QQ11 to 1

\ Fall through into TT110 to show the front space view

Type: Subroutine
Category: Flight
Summary: Launch from a station or show the front space view
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* Ghy calls TT110
* TT102 calls TT110

Launch the ship (if we are docked), or show the front space view (if we are

Called when red key f0 is pressed while docked (launch), after we arrive in a
new galaxy, or after a hyperspace if the current view is a space view.

.TT110

LDX QQ12               \ If we are not docked (QQ12 = 0) then jump to NLUNCH
BEQ NLUNCH             \ to skip the launch tunnel and setup process

JSR LAUN               \ Show the space station launch tunnel

JSR RES2               \ Reset a number of flight variables and workspaces

JSR TT111              \ Select the system closest to galactic coordinates
\ (QQ9, QQ10)

INC INWK+8             \ Increment z_sign ready for the call to SOS, so the
\ planet appears at a z_sign of 1 in front of us when
\ we launch

JSR SOS1               \ Call SOS1 to set up the planet's data block and add it
\ to FRIN, where it will get put in the first slot as
\ it's the first one to be added to our local bubble of
\ universe following the call to RES2 above

LDA #128               \ For the space station, set z_sign to &80, so it's
STA INWK+8             \ behind us (&80 is negative)

INC INWK+7             \ And increment z_hi, so it's only just behind us

JSR NWSPS              \ Add a new space station to our local bubble of
\ universe

LDA #12                \ Set our launch speed in DELTA to 12
STA DELTA

JSR BAD                \ Call BAD to work out how much illegal contraband we
\ are carrying in our hold (A is up to 40 for a
\ standard hold crammed with contraband, up to 70 for
\ an extended cargo hold full of narcotics and slaves)

ORA FIST               \ OR the value in A with our legal status in FIST to
\ get a new value that is at least as high as both
\ values, to reflect the fact that launching with a
\ hold full of contraband can only make matters worse

STA FIST               \ Update our legal status with the new value

LDA #255               \ Set the view number in QQ11 to 255
STA QQ11

JSR HFS1               \ Call HFS1 to draw 8 concentric rings

.NLUNCH

LDX #0                 \ Set QQ12 to 0 to indicate we are not docked
STX QQ12

JMP LOOK1              \ Jump to LOOK1 to switch to the front view (X = 0),
\ returning from the subroutine using a tail call

Type: Subroutine
Category: Charts
Summary: Display either the Long-range or Short-range Chart
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT18 calls TT114

Display either the Long-range or Short-range Chart, depending on the current
view setting. Called from TT18 once we know the current view is one of the
charts.

Arguments:

A                    The current view, loaded from QQ11

.TT114

BMI TT115              \ If bit 7 of the current view is set (i.e. the view is

JMP TT22               \ Otherwise the current view is the Long-range Chart, so

.TT115

Type: Subroutine
Category: Maths (Arithmetic)
Summary: Add an amount of cash to the cash pot
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* Main flight loop (Part 12 of 16) calls MCASH

Add (Y X) cash to the cash pot in CASH. As CASH is a four-byte number, this
calculates:

CASH(0 1 2 3) = CASH(0 1 2 3) + (Y X)

Other entry points:

TT113                Contains an RTS

.MCASH

TXA                    \ Add the least significant bytes:
CLC                    \
ADC CASH+3             \   CASH+3 = CASH+3 + X
STA CASH+3

TYA                    \ Then the second most significant bytes:
STA CASH+2             \   CASH+2 = CASH+2 + Y

\ --- Mod: Original Acornsoft code removed: ----------->

\ LDA CASH+1            \ Then the third most significant bytes (which are 0):
\ STA CASH+1            \   CASH+1 = CASH+1 + 0

\ LDA CASH              \ And finally the most significant bytes (which are 0):
\ STA CASH              \   CASH = CASH + 0

\ --- And replaced by: -------------------------------->

BCC TT113              \ If the above addition didn't overflow, then the
\ subroutine with the C flag clear

INC CASH+1             \ Otherwise we need to add the C flag to the third most
\ significant byte of CASH, which we can do with an
\ increment

BNE n_addmny           \ If the result of the above increment is non-zero, then
\ we have nothing further to carry and the addition is
\ complete, so skip the following instruction

INC CASH               \ Otherwise we need to add the C flag to the most
\ significant byte of CASH, which we can do with an
\ increment

\ --- End of replacement ------------------------------>

CLC                    \ Clear the C flag, so if the above was done following
\ a failed LCASH call, the C flag correctly indicates
\ failure

.TT113

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Maths (Arithmetic)
Summary: Calculate (Y X) = P * Q * 4
Context: See this subroutine on its own page
References: No direct references to this subroutine in this source file

Calculate the following multiplication of unsigned 8-bit numbers:

(Y X) = P * Q * 4

\ --- Mod: Original Acornsoft code removed: ----------->

\.GCASH

\ JSR MULTU             \ Call MULTU to calculate (A P) = P * Q

\ --- End of removed code ----------------------------->

Type: Subroutine
Category: Maths (Arithmetic)
Summary: Calculate (Y X) = (A P) * 4
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT151 calls GC2

Calculate the following multiplication of unsigned 16-bit numbers:

(Y X) = (A P) * 4

Other entry points:

price_xy             Set (Y X) = (A P)

.GC2

ASL P                  \ Set (A P) = (A P) * 4
ROL A
ASL P
ROL A

\ --- Mod: Code added for Elite-A: -------------------->

.price_xy

\ --- End of added code ------------------------------->

TAY                    \ Set (Y X) = (A P)
LDX P

RTS                    \ Return from the subroutine

Type: Subroutine
Category: Charts
Summary: Select the closest system and redraw the chart crosshairs
Context: See this subroutine on its own page
References: This subroutine is called as follows:
* TT102 calls hm
* hyp calls hm

Set the system closest to galactic coordinates (QQ9, QQ10) as the selected
system, redraw the crosshairs on the chart accordingly (if they are being
shown), and, if this is not a space view, clear the bottom three text rows of
the screen.

.hm

JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
\ which will erase the crosshairs currently there

JSR TT111              \ Select the system closest to galactic coordinates
\ (QQ9, QQ10)

JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10),
\ which will draw the crosshairs at our current home
\ system

JMP CLYNS              \ Clear the bottom three text rows of the upper screen,
\ and move the text cursor to column 1 on row 21, i.e.
\ the start of the top row of the three bottom rows

\ Return from the subroutine using a tail call

Save ELTD.bin

PRINT "ELITE D"
PRINT "Assembled at ", ~CODE_D%
PRINT "Ends at ", ~P%
PRINT "Code size is ", ~(P% - CODE_D%)