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