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cc65/libsrc/runtime/mulax9.s

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;
; Ullrich von Bassewitz, 16.03.2002
;
; CC65 runtime: Multiply the primary register
;
.export mulax9
.importzp ptr1, tmp1
.proc mulax9
sta ptr1
stx ptr1+1
stx tmp1
asl a
rol tmp1 ; * 2
asl a
rol tmp1 ; * 4
asl a
rol tmp1 ; * 8
clc
adc ptr1 ; * (8+1)
pha
lda tmp1
adc ptr1+1
tax
pla
rts
.endproc