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;
; Ullrich von Bassewitz, 2011-07-10
;
; CC65 runtime: 8x16 => 24 unsigned multiplication
;
.export umul8x16r24, umul8x16r24m
.export umul8x16r16, umul8x16r16m
.include "zeropage.inc"
.macpack cpu
;---------------------------------------------------------------------------
; 8x16 => 24 unsigned multiplication routine. Because the overhead for a
; 8x16 => 16 unsigned multiplication routine is small, we will tag it with
; the matching labels, as well.
;
; routine LHS RHS result result also in
; -----------------------------------------------------------------------
; umul8x16r24 ax ptr1-low ax:sreg-low ptr1:sreg-low
; umul8x16r24m ptr3 ptr1-low ax:sreg-low ptr1:sreg-low
;
; ptr3 is left intact by the routine.
;
umul8x16r24:
umul8x16r16:
sta ptr3
stx ptr3+1
umul8x16r24m:
umul8x16r16m:
.if (.cpu .bitand ::CPU_ISET_65SC02)
stz ptr1+1
stz sreg
.else
ldx #0
stx ptr1+1
stx sreg
.endif
ldy #8 ; Number of bits
ldx ptr3 ; Get into register for speed
lda ptr1
ror a ; Get next bit into carry
@L0: bcc @L1
clc
pha
txa
adc ptr1+1
sta ptr1+1
lda ptr3+1
adc sreg
sta sreg
pla
@L1: ror sreg
ror ptr1+1
ror a
dey
bne @L0
sta ptr1 ; Save low byte of result
ldx ptr1+1 ; Load high byte of result
rts ; Done
|
