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cc65/libsrc/runtime/sub.s

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;
; Ullrich von Bassewitz, 05.08.1998
;
; CC65 runtime: sub ints
;
.export tossuba0, tossubax
.import addysp1
.importzp sp, ptr1
;
; AX = TOS - AX
;
tossuba0:
ldx #0
tossubax:
ldy #0
sta ptr1
stx ptr1+1
lda (sp),y ; lo byte
sec
sbc ptr1
sta ptr1 ; save lo byte
iny
lda (sp),y
sbc ptr1+1
tax
lda ptr1
jmp addysp1 ; drop TOS, set condition codes