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Elite on the BBC Micro

Version analysis of HME2

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Name: HME2 Type: Subroutine Category: Charts Summary: Search the galaxy for a system
.HME2

Code variation 1 of 2Related to the screen mode

This variation is blank in the Disc (docked) version.

Tap on a version to expand it, and tap it again to show to all variations.

Master

6502SP

LDA #CYAN \ Switch to colour 3, which is white in the chart view STA COL
LDA #CYAN \ Send a #SETCOL CYAN command to the I/O processor to JSR DOCOL \ switch to colour 3, which is white in the chart view
 LDA #14                \ Print extended token 14 ("{clear bottom of screen}
 JSR DETOK              \ PLANET NAME?{fetch line input from keyboard}"). The
                        \ last token calls MT26, which puts the entered search
                        \ term in INWK+5 and the term length in Y

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

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

 LDA #0                 \ We now loop through the galaxy's systems in order,
 STA XX20               \ until we find a match, so set XX20 to act as a system
                        \ counter, starting with system 0

.HME3

 JSR MT14               \ Switch to justified text when printing extended
                        \ tokens, so the call to cpl prints into the justified
                        \ text buffer at BUF instead of the screen, and DTW5
                        \ gets set to the length of the system name

 JSR cpl                \ Print the selected system name into the justified text
                        \ buffer

 LDX DTW5               \ Fetch DTW5 into X, so X is now equal to the length of
                        \ the selected system name

 LDA INWK+5,X           \ Fetch the X-th character from the entered search term

 CMP #13                \ If the X-th character is not a carriage return, then
 BNE HME6               \ the selected system name and the entered search term
                        \ are different lengths, so jump to HME6 to move on to
                        \ the next system

.HME4

 DEX                    \ Decrement X so it points to the last letter of the
                        \ selected system name (and, when we loop back here, it
                        \ points to the next letter to the left)

 LDA INWK+5,X           \ Set A to the X-th character of the entered search term

 ORA #%00100000         \ Set bit 5 of the character to make it lower case

 CMP BUF,X              \ If the character in A matches the X-th character of
 BEQ HME4               \ the selected system name in BUF, loop back to HME4 to
                        \ check the next letter to the left

 TXA                    \ The last comparison didn't match, so copy the letter
 BMI HME5               \ number into A, and if it's negative, that means we
                        \ managed to go past the first letters of each term
                        \ before we failed to get a match, so the terms are the
                        \ same, so jump to HME5 to process a successful search

.HME6

                        \ If we get here then the selected system name and the
                        \ entered search term did not match

 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               \ Incrememt the system counter in XX20

 BNE HME3               \ If we haven't yet checked all 256 systems in the
                        \ current galaxy, loop back to HME3 to check the next
                        \ system

                        \ If we get here then the entered search term did not
                        \ match any systems in the current galaxy

 JSR TT111              \ Select the system closest to galactic coordinates
                        \ (QQ9, QQ10), so we can put the crosshairs back where
                        \ they were before the search

 JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10)

Code variation 2 of 2Minor and very low-impact

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Docked, 6502SP

Master

LDA #40 \ Call the NOISE routine with A = 40 to make a low, JSR NOISE \ long beep to indicate a failed search
JSR LOWBEEP \ Call the LOWBEEP routine to make a low, long beep to \ indicate a failed search
 LDA #215               \ Print extended token 215 ("{left align} UNKNOWN
 JMP DETOK              \ PLANET"), which will print on-screem as the left align
                        \ code disables justified text, and return from the
                        \ subroutine using a tail call

.HME5

                        \ If we get here then we have found a match for the
                        \ entered search

 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 the x-coordinate of the search result

 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 the y-coordinate of the search result

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

 JSR TT103              \ Draw small crosshairs at coordinates (QQ9, QQ10)

 JSR MT15               \ Switch to left-aligned text when printing extended
                        \ tokens so future tokens will print to the screen (as
                        \ this disables justified text)

 JMP T95                \ Jump to T95 to print the distance to the selected
                        \ system and return from the subroutine using a tail
                        \ call

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