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Elite on the BBC Micro

Charts: HME2 [Elite-A, Parasite]

Name: HME2 [Show more] Type: Subroutine Category: Charts Summary: Search the galaxy for a system
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * TT102 calls HME2
.HME2 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) LDA #40 \ Call the NOISE routine with A = 40 to make a low, JSR NOISE \ 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