mirror of
https://github.com/cc65/cc65.git
synced 2024-11-16 02:10:52 +00:00
89 lines
2.0 KiB
ArmAsm
89 lines
2.0 KiB
ArmAsm
;
|
|
; 2010-11-02, Ullrich von Bassewitz
|
|
; 2014-09-10, Greg King
|
|
; 2019-11-05, Piotr Fusik
|
|
;
|
|
; CC65 runtime: 8x8 => 16 signed multiplication
|
|
;
|
|
|
|
.export imul8x8r16, imul8x8r16m
|
|
.importzp ptr1, ptr3, tmp1
|
|
|
|
.macpack generic
|
|
|
|
;---------------------------------------------------------------------------
|
|
; 8x8 => 16 signed multiplication routine.
|
|
;
|
|
; multiplicand multiplier product
|
|
; LHS RHS result
|
|
; -------------------------------------------------------------
|
|
; .A (ptr3-low) ptr1-low .XA
|
|
;
|
|
|
|
imul8x8r16:
|
|
sta ptr3
|
|
|
|
imul8x8r16m:
|
|
; Extend sign of Left-Hand Side
|
|
lda #$7f
|
|
cmp ptr3
|
|
adc #$80
|
|
sta ptr3+1
|
|
|
|
; Clear .XY accumulator
|
|
ldy #<$0000
|
|
ldx #>$0000
|
|
|
|
; Check the multiplier sign.
|
|
lda ptr1
|
|
bpl PosStart
|
|
|
|
; The multiplier is negative.
|
|
; Therefore, make it positive; and, subtract when multiplying.
|
|
NegMult:
|
|
eor #%11111111
|
|
sta ptr1
|
|
inc ptr1
|
|
bnz NegStart ; Branch always
|
|
|
|
NegAdd:
|
|
tya ; Subtract current multiplicand
|
|
; sec
|
|
sbc ptr3
|
|
tay
|
|
txa
|
|
sbc ptr3+1
|
|
tax
|
|
|
|
NegShift:
|
|
asl ptr3
|
|
rol ptr3+1
|
|
NegStart:
|
|
lsr ptr1 ; Get next bit of Right-Hand Side into carry
|
|
bcs NegAdd
|
|
bnz NegShift ; Loop if more one-bits in multiplier
|
|
|
|
tya ; Put result into cc65's accumulator
|
|
rts
|
|
|
|
; The multiplier is positive.
|
|
|
|
PosAdd:
|
|
tya ; Add current multiplicand
|
|
add ptr3
|
|
tay
|
|
txa
|
|
adc ptr3+1
|
|
tax
|
|
|
|
PosShift:
|
|
asl ptr3
|
|
rol ptr3+1
|
|
PosStart:
|
|
lsr ptr1 ; Get next bit of Right-Hand Side into carry
|
|
bcs PosAdd
|
|
bnz PosShift ; Loop if more one-bits in multiplier
|
|
|
|
tya ; Put result into cc65's accumulator
|
|
rts
|