mirror of
https://github.com/cc65/cc65.git
synced 2024-11-05 08:05:51 +00:00
f82a43b98d
A description of positions [left, right] is appropriate more for C code than for Assembly code. (A description of timing [first argument, second argument] is more appropriate for the way that Assembly code is written.)
36 lines
965 B
ArmAsm
36 lines
965 B
ArmAsm
;
|
|
; Ullrich von Bassewitz, 2010-11-02
|
|
;
|
|
; CC65 runtime: 8x8 => 16 unsigned multiplication
|
|
;
|
|
|
|
.export umul8x8r16, umul8x8r16m
|
|
.importzp ptr1, ptr3
|
|
|
|
|
|
;---------------------------------------------------------------------------
|
|
; 8x8 => 16 unsigned multiplication routine.
|
|
;
|
|
; LHS RHS result result in also
|
|
; -------------------------------------------------------------
|
|
; .A (ptr3-low) ptr1-low .XA ptr1
|
|
;
|
|
|
|
umul8x8r16:
|
|
sta ptr3
|
|
umul8x8r16m:
|
|
lda #0 ; Clear byte 1
|
|
ldy #8 ; Number of bits
|
|
lsr ptr1 ; Get first bit of RHS into carry
|
|
@L0: bcc @L1
|
|
clc
|
|
adc ptr3
|
|
@L1: ror
|
|
ror ptr1
|
|
dey
|
|
bne @L0
|
|
tax
|
|
stx ptr1+1 ; Result in .XA and ptr1
|
|
lda ptr1 ; Load the result
|
|
rts ; Done
|