emailler/client/ip65/arithmetic.s

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.include "../inc/common.i"
;helper routines for arithmetic on 32 bit numbers
;reuse the copy_* zero page locations as pointers for 32bit addition
.importzp copy_src
.importzp copy_dest
acc32 =copy_src ;32bit accumulater (pointer)
op32 =copy_dest ;32 bit operand (pointer)
acc16 =acc32 ;16bit accumulater (value, NOT pointer)
.bss
temp_ax: .res 2
.code
;no 16bit operand as can just use AX
.exportzp acc32
.exportzp op32
.exportzp acc16
.export add_32_32
.export add_16_32
.export sub_16_16
.export cmp_32_32
.export cmp_16_16
.export mul_8_16
;compare 2 32bit numbers
;on exit, zero flag clear iff acc32==op32
cmp_32_32:
ldy #0
lda (op32),y
cmp (acc32),y
bne @exit
iny
lda (op32),y
cmp (acc32),y
bne @exit
iny
lda (op32),y
cmp (acc32),y
bne @exit
iny
lda (op32),y
cmp (acc32),y
@exit:
rts
;compare 2 16bit numbers
;on exit, zero flag clear iff acc16==AX
cmp_16_16:
cmp acc16
bne @exit
txa
cmp acc16+1
@exit:
rts
;subtract 2 16 bit numbers
;acc16=acc16-AX
sub_16_16:
stax temp_ax
sec
lda acc16
sbc temp_ax
sta acc16
lda acc16+1
sbc temp_ax+1
sta acc16+1
rts
;add a 32bit operand to the 32 bit accumulater
;acc32=acc32+op32
add_32_32:
clc
ldy #0
lda (op32),y
adc (acc32),y
sta (acc32),y
iny
lda (op32),y
adc (acc32),y
sta (acc32),y
iny
lda (op32),y
adc (acc32),y
sta (acc32),y
iny
lda (op32),y
adc (acc32),y
sta (acc32),y
rts
;add a 16bit operand to the 32 bit accumulater
;acc32=acc32+AX
add_16_32:
clc
ldy #0
adc (acc32),y
sta (acc32),y
iny
txa
adc (acc32),y
sta (acc32),y
iny
lda #0
adc (acc32),y
sta (acc32),y
iny
lda #0
adc (acc32),y
sta (acc32),y
rts
;multiply a 16 bit number by an 8 bit number
;acc16=acc16*a
mul_8_16:
tax
beq @operand_is_zero
lda acc16
sta temp_ax
lda acc16+1
sta temp_ax+1
@addition_loop:
dex
beq @done
clc
lda acc16
adc temp_ax
sta acc16
lda acc16+1
adc temp_ax+1
sta acc16+1
jmp @addition_loop
@done:
rts
@operand_is_zero:
sta acc16
sta acc16+1
rts