70 lines
1.2 KiB
ArmAsm
70 lines
1.2 KiB
ArmAsm
|
.define Mli2, Mlinp, Mul
|
||
|
|
|
||
|
|
! The subroutine Mli2 multiplies two signed integers. The integers
|
||
|
|
! are popped from the stack.
|
||
|
|
! The subroutine Mlinp expects the two integer to be in zeropage.
|
||
|
|
! While the subroutine Mul an unsigned multiply subroutine is.
|
||
|
|
! For the algoritme see A. S. Tanenbaum
|
||
|
|
! Structured Computer Organisation. 1976.
|
||
|
|
|
||
|
|
|
||
|
|
Mli2:
|
||
|
|
stx ARTH
|
||
|
|
sta ARTH+1
|
||
|
|
jsr Pop
|
||
|
|
stx ARTH+2
|
||
|
|
sta ARTH+3
|
||
|
|
Mlinp: ldy #1
|
||
|
|
sty UNSIGN ! it's signed
|
||
|
|
lda ARTH+1
|
||
|
|
bpl 3f ! multiplier negative so:
|
||
|
|
ldx ARTH
|
||
|
|
jsr Ngi2 ! negate multiplier
|
||
|
|
stx ARTH
|
||
|
|
sta ARTH+1
|
||
|
|
ldx ARTH+2
|
||
|
|
lda ARTH+3
|
||
|
|
jsr Ngi2 ! negate multiplicand
|
||
|
|
stx ARTH+2
|
||
|
|
sta ARTH+3
|
||
|
|
Mul:
|
||
|
|
3: lda #0
|
||
|
|
sta ARTH+4
|
||
|
|
sta ARTH+5
|
||
|
|
sta ARTH+6
|
||
|
|
sta ARTH+7 ! clear accumulator
|
||
|
|
ldy #16
|
||
|
|
1: lda #1h
|
||
|
|
bit ARTH
|
||
|
|
beq 2f ! multiplying by zero: no addition
|
||
|
|
clc
|
||
|
|
lda ARTH+6
|
||
|
|
adc ARTH+2
|
||
|
|
sta ARTH+6
|
||
|
|
lda ARTH+7
|
||
|
|
adc ARTH+3
|
||
|
|
sta ARTH+7
|
||
|
|
2: lsr ARTH+1
|
||
|
|
ror ARTH ! shift multiplier
|
||
|
|
lsr ARTH+7
|
||
|
|
ror ARTH+6
|
||
|
|
ror ARTH+5
|
||
|
|
ror ARTH+4 ! shift accumulator
|
||
|
|
lda UNSIGN
|
||
|
|
beq 3f ! unsigned multiply: so no shift in of signbit
|
||
|
|
lda ARTH+3
|
||
|
|
bpl 3f
|
||
|
|
lda #40h
|
||
|
|
bit ARTH+7
|
||
|
|
beq 3f
|
||
|
|
lda ARTH+7
|
||
|
|
ora #80h
|
||
|
|
sta ARTH+7
|
||
|
|
3: dey
|
||
|
|
bne 1b
|
||
|
|
ldx ARTH+4
|
||
|
|
lda ARTH+5
|
||
|
|
rts
|
||
|
|
|
||
|
|
|