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;
; Ullrich von Bassewitz, 07.04.2000
; Christian Krueger, 12-Mar-2017, added 65SC02 optimization
;
; CC65 runtime: -= operator
;
; On entry, the low byte of the address of the variable to decrement is
; in ptr1, the high byte is in Y, and the decrement is in eax.
;
.export lsubeq1, lsubeqa, lsubeq
.importzp sreg, ptr1
.macpack cpu
lsubeq1:
lda #$01
lsubeqa:
ldx #$00
stx sreg
stx sreg+1
lsubeq: sty ptr1+1 ; Store high byte of address
sec
eor #$FF
.if (.cpu .bitand ::CPU_ISET_65SC02)
adc (ptr1) ; Subtract byte 0
sta (ptr1)
ldy #$01 ; Address byte 1
.else
ldy #$00 ; Address low byte
adc (ptr1),y ; Subtract byte 0
sta (ptr1),y
iny ; Address byte 1
.endif
pha ; Save byte 0 of result for later
txa
eor #$FF
adc (ptr1),y ; Subtract byte 1
sta (ptr1),y
tax
iny ; Address byte 2
lda (ptr1),y
sbc sreg
sta (ptr1),y
sta sreg
iny ; Address byte 3
lda (ptr1),y
sbc sreg+1
sta (ptr1),y
sta sreg+1
pla ; Retrieve byte 0 of result
rts ; Done
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