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cc65/libsrc/atari5200/mul20.s

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;
; Christian Groessler, April 2014
;
; mul20
; multiplies A by 20 and returns result in AX
; uses tmp4
.importzp tmp4
.export mul20,loc_tmp
.proc mul20
ldx #0
stx tmp4
sta loc_tmp
asl a
rol tmp4
asl a
rol tmp4 ; val * 4
adc loc_tmp
bcc L1
inc tmp4 ; val * 5
L1: asl a
rol tmp4 ; val * 10
asl a
rol tmp4 ; val * 20
ldx tmp4
rts
.endproc
.bss
loc_tmp:.res 1