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entropy: shave another byte off thanks to Nick Westgate

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Vince Weaver 2018-05-31 12:47:28 -04:00
parent 59025a1d5d
commit 25a8d7b497
3 changed files with 15 additions and 9 deletions
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2
two-liners/README.entropy
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@ -52,7 +52,7 @@ This sound simple, but it leads to some neat patterns.
=======================
I thought it would be neat to see how small I could make this in assembly
language. Currently I have it down to 119 bytes (the executable is 123
language. Currently I have it down to 118 bytes (the executable is 122
bytes because DOS33 includes size/address filesystem metadata in the file
itself).

BIN
two-liners/entropy.dsk
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22
two-liners/entropy.s
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@ -2,7 +2,7 @@
; by Dave McKellar of Toronto
; Two-line BASIC program
; Found on Beagle Brother's Apple Mechanic Disk
; Converted to 6502 Assembly by Vince Weaver
; Converted to 6502 Assembly by Deater (Vince Weaver) vince@deater.net
; 24001 ROT=0:FOR I=1 TO 15: READ A,B: POKE A,B: NEXT: DATA
; 232,252,233,29,7676,1,7678,4,7679,0,7680,18,7681,63,
@ -26,9 +26,12 @@
; 126 bytes: nextx: simplify by using knowledge of possible x/y vals
; 124 bytes: qkumba noticed we can bump yloop up to include the
; pha, letting us remove two now unneeded stack ops
; 123 byts: qkumba noticed XDRAW0 always exits with X==0 so
; 123 bytes: qkumba noticed XDRAW0 always exits with X==0 so
; we can move some things to use X instead and
; can get a "1" value simply by using INX
; 122 bytes: Nick Westgate noticed that we could save a byte
; in eloop by pushing the stx ELOOP to the beginning
; rather than the end.
;BLT=BCC, BGE=BCS
@ -69,11 +72,14 @@ XDRAW0 = $F65D
entropy:
jsr HGR2 ; Hi-res graphics, no text at bottom
; Y=0, A=$60 after this call
lda #8 ; Unlike the BASIC, our loop is *100
sta EPOS ; 8 to 15 rather than .08 to .15
ldx #8 ; Unlike the BASIC, our loop is *100
; 8 to 15 rather than .08 to .15
eloop:
stx EPOS ; EPOS was temporarily in X
lda #4 ; FOR Y=4 to 189 STEP 6
yloop:
pha ; YPOS stored on stack
@ -196,9 +202,9 @@ nexty: ; NEXT Y
bcc yloop ; if so, loop
nexte: ; NEXT E
inc EPOS
lda EPOS
cmp #15
ldx EPOS
inx ; EPOS saved at beginning og eloop
cpx #15
bcc eloop ; branch if <15
bcs entropy