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58 lines
2.9 KiB
58 lines
2.9 KiB
2 years ago
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This program provides a formatted listing of a BBC BASIC program, by splitting multiple statements out onto separate lines, indenting loops, etc. Assembly language also gets nicely formatted.
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I was doing a lot of work on the BBC Micro in the late 80's, and recently managed to retrieve a lot of it from floppy discs. The discs were in relatively good condition, given that they were nearly 40 years old (!), but it was still a challenge reading them (they were shedding so much oxide, we had to clean the disk heads after each use :-)).
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This program was incredibly useful, but we were only able to get a binary executable off the floppies, not the source code, so I disassembled it, annotated it, and have made it available here.
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Working on the BBC Micro was not easy, since you only had, at best, 24¾KB of memory (!) (5¾KB if you were using hi-res graphics), so saving every byte of memory possible was really important. Since BASIC is an interpreted language, and each line had a 3-byte overhead, you could save quite a few bytes by cramming as many statements onto each line as possible, separated by a colon, thus saving 2 bytes for each statement.
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Of course, this made the code very difficult to read, so I wrote this listing formatter, which converts something like this:
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```
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807DEFPROCsp LOCALT%,I%,P%,S$:PROCblip(100):REPEATUNTILNOTINKEY-99:REPEAT:PRINTTAB(0,24)SPC10f$B$bk$Y$"Press SPACE "bb$SPC10;:PROCfx21:T%=INKEY500:IFT%=esc T%=FNesc(T%):GOTO810:ELSEIFT%=32ORT%<>-1ORRND(500)>1GOTO810
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809P%=msgs+1:FORI%=1TORND(?msgs):S$=$P%:P%=P%+LENS$+1:NEXT:prvb=prvb+1:PRINTTAB(0,24)CHR$(128+RND(7))SPC38;:I%=1:REPEAT:PRINTTAB(1,24)MID$(STRING$(39," ")+"Ancient proverb #"+STR$prvb+": "+S$+STRING$(50," "),I%,38);:I%=I%+1:UNTILI%=70+LENS$ORNOTINKEY20
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810UNTILT%=32:PRINTTAB(0,24)SPC39;:ENDPROC
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```
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into this:
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```
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807 DEFPROCsp LOCALT%,I%,P%,S$
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:PROCblip(100)
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:REPEATUNTILNOTINKEY-99
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:REPEAT
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: PRINTTAB(0,24)SPC10f$B$bk$Y$"Press SPACE "bb$SPC10;
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: PROCfx21
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: T%=INKEY500
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: IFT%=esc T%=FNesc(T%)
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: GOTO810
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: ELSEIFT%=32ORT%<>-1ORRND(500)>1GOTO810
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809 P%=msgs+1
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: FORI%=1TORND(?msgs)
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: S$=$P%
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: P%=P%+LENS$+1
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: NEXT
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: prvb=prvb+1
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: PRINTTAB(0,24)CHR$(128+RND(7))SPC38;
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: I%=1
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: REPEAT
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: PRINTTAB(1,24)MID$(STRING$(39," ")+"Ancient proverb #"+STR$prvb+": "+S$+STRING$(50," "),I%,38);
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: I%=I%+1
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: UNTILI%=70+LENS$ORNOTINKEY20
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810 UNTILT%=32
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:PRINTTAB(0,24)SPC39;
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:ENDPROC
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```
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To get the fully authentic Beeb experience, you can type the program in from the listing :-), but as a convenience, a `.ssd` file is provided with the source code, together with a binary executable.
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Load the program into memory like this:
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```
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*LST2
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```
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And then enter LIST commands as normal, but with a trailing period e.g.
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```
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LIST 100,200.
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LIST ,200.
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LIST 100,.
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LIST.
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```
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