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cc65/libsrc/runtime/lsub.s

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;
; Ullrich von Bassewitz, 05.08.1998
;
; CC65 runtime: long sub
;
;
; EAX = TOS - EAX
;
.export tossubeax
.import addysp1
.importzp sp, sreg, tmp1, tmp2
tossubeax:
ldy #0
sec
sta tmp1
lda (sp),y
sbc tmp1 ; byte 0
sta tmp2 ; use as temp storage
iny
stx tmp1
lda (sp),y
sbc tmp1 ; byte 1
tax
iny
lda (sp),y
sbc sreg ; byte 2
sta sreg
iny
lda (sp),y
sbc sreg+1 ; byte 3
sta sreg+1
lda tmp2 ; load byte 0
jmp addysp1 ; drop TOS