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entropy: optimize nextx

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This commit is contained in:
Vince Weaver 2018-05-28 00:27:25 -04:00
parent ed747e349f
commit 6a0aaeb009
1 changed files with 4 additions and 3 deletions
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7
two-liners/entropy.s
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@ -15,6 +15,7 @@
; Optimization ; Optimization
; 144 bytes: first working version (including DOS33 4-byte size/addr) ; 144 bytes: first working version (including DOS33 4-byte size/addr)
; 141 bytes: optimize "nextx" routine
;BLT=BCC, BGE=BCS ;BLT=BCC, BGE=BCS
@ -171,17 +172,17 @@ nextx: ; NEXT X
clc ; 1 clc ; 1
adc #6 ; x+=6 ; 2 adc #6 ; x+=6 ; 2
sta XPOS ; 2 sta XPOS ; 2
tax ; save in X for later ; 1
lda #0 ; inc high bit if we wrap past 256 ; 2 lda #0 ; inc high bit if we wrap past 256 ; 2
adc XPOSH ; 2 adc XPOSH ; 2
sta XPOSH ; 2 sta XPOSH ; 2
beq xloop ; if high byte zero, not at end ; 2 beq xloop ; if high byte zero, not at end ; 2
lda XPOS ; 2 cpx #22 ; see if less than 278 ; 2
cmp #22 ; see if less than 278 ; 2
bcc xloop ; if so, loop ; 2 bcc xloop ; if so, loop ; 2
;============ ;============
; 21 ; 20
nexty: ; NEXT Y nexty: ; NEXT Y
lda YPOS lda YPOS
clc clc