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Merge pull request #606 from pfusik/ldec

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Optimize deceaxy
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Oliver Schmidt 2018-03-10 11:28:46 +00:00 committed by GitHub
commit be30c0bd70
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1 changed files with 23 additions and 13 deletions
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36
libsrc/runtime/ldec.s
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@ -1,5 +1,6 @@
; ;
; Ullrich von Bassewitz, 29.12.1999 ; Piotr Fusik, 09.03.2018
; originally by Ullrich von Bassewitz
; ;
; CC65 runtime: Decrement eax by value in Y ; CC65 runtime: Decrement eax by value in Y
; ;
@ -11,16 +12,25 @@ deceaxy:
sty tmp1 sty tmp1
sec sec
sbc tmp1 sbc tmp1
sta tmp1 bcs @L9
txa
sbc #0 ; Borrow from X.
tax
lda sreg dex
sbc #0 cpx #$FF
sta sreg bne @L9
lda sreg+1
sbc #0 ; X wrapped from zero to $FF, borrow from sreg.
sta sreg+1
lda tmp1 dec sreg
rts cpx sreg
bne @L9
; sreg wrapped from zero to $FF, borrow from sreg+1.
dec sreg+1
; Done.
@L9: rts