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cc65/libsrc/runtime/add.s

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ArmAsm
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;
; Ullrich von Bassewitz, 05.08.1998
;
; CC65 runtime: add ints
;
; Make this as fast as possible, even if it needs more space since it's
; called a lot!
.export tosadda0, tosaddax
.importzp sp
.macpack cpu
tosadda0:
ldx #0
tosaddax:
clc
.if (.cpu .bitand CPU_ISET_65SC02)
adc (sp) ; 65SC02 version - saves 2 cycles
ldy #1
.else
ldy #0
adc (sp),y ; lo byte
iny
.endif
pha ; save it
txa
adc (sp),y ; hi byte
tax
clc
lda sp
adc #2
sta sp
bcc L1
inc sp+1
L1: pla ; Restore low byte
rts