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882 lines
16 KiB
NASM
882 lines
16 KiB
NASM
; Internal Math library routines - always included by the compiler
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; Generic machine independent 6502 code.
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;
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; some more interesting routines can be found here:
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; http://6502org.wikidot.com/software-math
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; http://codebase64.org/doku.php?id=base:6502_6510_maths
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; https://github.com/TobyLobster/multiply_test
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; https://github.com/TobyLobster/sqrt_test
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multiply_bytes .proc
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; -- multiply 2 bytes A and Y, result as byte in A (signed or unsigned)
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sta P8ZP_SCRATCH_B1 ; num1
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sty P8ZP_SCRATCH_REG ; num2
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lda #0
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beq _enterloop
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_doAdd clc
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adc P8ZP_SCRATCH_B1
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_loop asl P8ZP_SCRATCH_B1
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_enterloop lsr P8ZP_SCRATCH_REG
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bcs _doAdd
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bne _loop
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rts
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.pend
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multiply_bytes_into_word .proc
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; -- multiply 2 bytes A and Y, result as word in A/Y (unsigned)
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sta P8ZP_SCRATCH_B1
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sty P8ZP_SCRATCH_REG
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lda #0
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ldx #8
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lsr P8ZP_SCRATCH_B1
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- bcc +
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clc
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adc P8ZP_SCRATCH_REG
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+ ror a
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ror P8ZP_SCRATCH_B1
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dex
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bne -
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tay
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lda P8ZP_SCRATCH_B1
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rts
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.pend
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multiply_words .proc
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; -- multiply two 16-bit words into a 32-bit result (signed and unsigned)
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; input: A/Y = first 16-bit number, P8ZP_SCRATCH_W1 in ZP = second 16-bit number
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; output: multiply_words.result 4-bytes/32-bits product, LSB order (low-to-high) low 16 bits also in AY.
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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mult16 lda #0
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sta result+2 ; clear upper bits of product
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sta result+3
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ldx #16 ; for all 16 bits...
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- lsr P8ZP_SCRATCH_W1+1 ; divide multiplier by 2
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ror P8ZP_SCRATCH_W1
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bcc +
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lda result+2 ; get upper half of product and add multiplicand
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clc
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adc P8ZP_SCRATCH_W2
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sta result+2
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lda result+3
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adc P8ZP_SCRATCH_W2+1
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+ ror a ; rotate partial product
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sta result+3
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ror result+2
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ror result+1
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ror result
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dex
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bne -
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lda result
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ldy result+1
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rts
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result .byte 0,0,0,0
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.pend
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divmod_b_asm .proc
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; signed byte division: make everything positive and fix sign afterwards
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sta P8ZP_SCRATCH_B1
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tya
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eor P8ZP_SCRATCH_B1
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php ; save sign
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lda P8ZP_SCRATCH_B1
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bpl +
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eor #$ff
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sec
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adc #0 ; make it positive
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+ pha
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tya
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bpl +
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eor #$ff
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sec
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adc #0 ; make it positive
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tay
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+ pla
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jsr divmod_ub_asm
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sta _remainder
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plp
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bpl +
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tya
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eor #$ff
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sec
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adc #0 ; negate result
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tay
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+ rts
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_remainder .byte 0
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.pend
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divmod_ub_asm .proc
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; -- divide A by Y, result quotient in Y, remainder in A (unsigned)
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; division by zero will result in quotient = 255 and remainder = original number
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sty P8ZP_SCRATCH_REG
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sta P8ZP_SCRATCH_B1
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lda #0
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ldx #8
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asl P8ZP_SCRATCH_B1
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- rol a
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cmp P8ZP_SCRATCH_REG
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bcc +
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sbc P8ZP_SCRATCH_REG
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+ rol P8ZP_SCRATCH_B1
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dex
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bne -
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ldy P8ZP_SCRATCH_B1
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rts
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.pend
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divmod_w_asm .proc
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; signed word division: make everything positive and fix sign afterwards
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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lda P8ZP_SCRATCH_W1+1
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eor P8ZP_SCRATCH_W2+1
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php ; save sign
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lda P8ZP_SCRATCH_W1+1
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bpl +
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lda #0
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sec
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sbc P8ZP_SCRATCH_W1
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sta P8ZP_SCRATCH_W1
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lda #0
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sbc P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W1+1
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+ lda P8ZP_SCRATCH_W2+1
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bpl +
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lda #0
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sec
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sbc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W2
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lda #0
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sbc P8ZP_SCRATCH_W2+1
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sta P8ZP_SCRATCH_W2+1
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+ tay
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lda P8ZP_SCRATCH_W2
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jsr divmod_uw_asm
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plp ; restore sign
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bpl +
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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lda #0
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sec
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sbc P8ZP_SCRATCH_W2
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pha
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lda #0
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sbc P8ZP_SCRATCH_W2+1
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tay
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pla
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+ rts
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.pend
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divmod_uw_asm .proc
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; -- divide two unsigned words (16 bit each) into 16 bit results
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; input: P8ZP_SCRATCH_W1 in ZP: 16 bit number, A/Y: 16 bit divisor
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; output: P8ZP_SCRATCH_W2 in ZP: 16 bit remainder, A/Y: 16 bit division result
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; division by zero will result in quotient = 65535 and remainder = divident
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dividend = P8ZP_SCRATCH_W1
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remainder = P8ZP_SCRATCH_W2
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result = dividend ;save memory by reusing divident to store the result
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sta _divisor
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sty _divisor+1
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lda #0 ;preset remainder to 0
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sta remainder
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sta remainder+1
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ldx #16 ;repeat for each bit: ...
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- asl dividend ;dividend lb & hb*2, msb -> Carry
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rol dividend+1
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rol remainder ;remainder lb & hb * 2 + msb from carry
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rol remainder+1
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lda remainder
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sec
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sbc _divisor ;substract divisor to see if it fits in
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tay ;lb result -> Y, for we may need it later
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lda remainder+1
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sbc _divisor+1
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bcc + ;if carry=0 then divisor didn't fit in yet
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sta remainder+1 ;else save substraction result as new remainder,
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sty remainder
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inc result ;and INCrement result cause divisor fit in 1 times
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+ dex
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bne -
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lda result
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ldy result+1
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rts
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_divisor .word 0
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.pend
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randword .proc
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; -- 16 bit pseudo random number generator into AY
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; default seed = $00c2 $1137
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; routine from https://codebase64.org/doku.php?id=base:x_abc_random_number_generator_8_16_bit
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inc x1
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clc
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x1=*+1
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lda #$00 ;x1
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c1=*+1
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eor #$c2 ;c1
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a1=*+1
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eor #$11 ;a1
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sta a1
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b1=*+1
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adc #$37 ;b1
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sta b1
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lsr a
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eor a1
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adc c1
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sta c1
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ldy b1
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rts
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.pend
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randbyte = randword ; -- 8 bit pseudo random number generator into A (by just reusing randword)
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; ----------- optimized multiplications (in-place A (byte) and ?? (word)) : ---------
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mul_byte_3 .proc
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; A = A + A*2
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sta P8ZP_SCRATCH_REG
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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rts
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.pend
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mul_word_3 .proc
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; AY = AY*2 + AY
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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lda P8ZP_SCRATCH_W1+1
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adc P8ZP_SCRATCH_W2+1
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tay
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lda P8ZP_SCRATCH_W1
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rts
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.pend
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mul_byte_5 .proc
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; A = A*4 + A
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sta P8ZP_SCRATCH_REG
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asl a
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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rts
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.pend
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mul_word_5 .proc
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; AY = AY*4 + AY
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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lda P8ZP_SCRATCH_W1+1
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adc P8ZP_SCRATCH_W2+1
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tay
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lda P8ZP_SCRATCH_W1
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rts
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.pend
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mul_byte_6 .proc
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; A = (A*2 + A)*2
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sta P8ZP_SCRATCH_REG
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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asl a
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rts
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.pend
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mul_word_6 .proc
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; AY = (AY*2 + AY)*2
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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tay
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lda P8ZP_SCRATCH_W1+1
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adc P8ZP_SCRATCH_W2+1
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sta P8ZP_SCRATCH_W1+1
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tya
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asl a
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rol P8ZP_SCRATCH_W1+1
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ldy P8ZP_SCRATCH_W1+1
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rts
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.pend
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mul_byte_7 .proc
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; A = A*8 - A
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sta P8ZP_SCRATCH_REG
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asl a
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asl a
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asl a
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sec
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sbc P8ZP_SCRATCH_REG
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rts
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.pend
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mul_word_7 .proc
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; AY = AY*8 - AY
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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sec
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sbc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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lda P8ZP_SCRATCH_W1+1
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sbc P8ZP_SCRATCH_W2+1
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tay
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lda P8ZP_SCRATCH_W1
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rts
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.pend
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mul_byte_9 .proc
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; A = A*8 + A
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sta P8ZP_SCRATCH_REG
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asl a
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asl a
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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rts
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.pend
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mul_word_9 .proc
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; AY = AY*8 + AY
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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lda P8ZP_SCRATCH_W1+1
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adc P8ZP_SCRATCH_W2+1
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tay
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lda P8ZP_SCRATCH_W1
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rts
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rts
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.pend
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mul_byte_10 .proc
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; A=(A*4 + A)*2
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sta P8ZP_SCRATCH_REG
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asl a
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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asl a
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rts
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.pend
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mul_word_10 .proc
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; AY=(AY*4 + AY)*2
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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lda P8ZP_SCRATCH_W1+1
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adc P8ZP_SCRATCH_W2+1
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sta P8ZP_SCRATCH_W1+1
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lda P8ZP_SCRATCH_W1
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asl a
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rol P8ZP_SCRATCH_W1+1
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ldy P8ZP_SCRATCH_W1+1
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rts
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.pend
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mul_byte_11 .proc
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; A=(A*2 + A)*4 - A
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sta P8ZP_SCRATCH_REG
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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asl a
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asl a
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sec
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sbc P8ZP_SCRATCH_REG
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rts
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.pend
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; mul_word_11 is skipped (too much code)
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mul_byte_12 .proc
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; A=(A*2 + A)*4
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sta P8ZP_SCRATCH_REG
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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asl a
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asl a
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rts
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.pend
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mul_word_12 .proc
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; AY=(AY*2 + AY)*4
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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clc
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adc P8ZP_SCRATCH_W2
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sta P8ZP_SCRATCH_W1
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lda P8ZP_SCRATCH_W1+1
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adc P8ZP_SCRATCH_W2+1
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sta P8ZP_SCRATCH_W1+1
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lda P8ZP_SCRATCH_W1
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asl a
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rol P8ZP_SCRATCH_W1+1
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asl a
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rol P8ZP_SCRATCH_W1+1
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ldy P8ZP_SCRATCH_W1+1
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rts
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.pend
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mul_byte_13 .proc
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; A=(A*2 + A)*4 + A
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sta P8ZP_SCRATCH_REG
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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asl a
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asl a
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clc
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adc P8ZP_SCRATCH_REG
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rts
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.pend
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; mul_word_13 is skipped (too much code)
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mul_byte_14 .proc
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; A=(A*8 - A)*2
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sta P8ZP_SCRATCH_REG
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asl a
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asl a
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asl a
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sec
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sbc P8ZP_SCRATCH_REG
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asl a
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rts
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.pend
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; mul_word_14 is skipped (too much code)
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mul_byte_15 .proc
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; A=A*16 - A
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sta P8ZP_SCRATCH_REG
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asl a
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asl a
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asl a
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asl a
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sec
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sbc P8ZP_SCRATCH_REG
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rts
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.pend
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mul_word_15 .proc
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; AY = AY * 16 - AY
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sta P8ZP_SCRATCH_W1
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sty P8ZP_SCRATCH_W1+1
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sta P8ZP_SCRATCH_W2
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sty P8ZP_SCRATCH_W2+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
sec
|
|
sbc P8ZP_SCRATCH_W2
|
|
sta P8ZP_SCRATCH_W1
|
|
lda P8ZP_SCRATCH_W1+1
|
|
sbc P8ZP_SCRATCH_W2+1
|
|
tay
|
|
lda P8ZP_SCRATCH_W1
|
|
rts
|
|
.pend
|
|
|
|
mul_byte_20 .proc
|
|
; A=(A*4 + A)*4
|
|
sta P8ZP_SCRATCH_REG
|
|
asl a
|
|
asl a
|
|
clc
|
|
adc P8ZP_SCRATCH_REG
|
|
asl a
|
|
asl a
|
|
rts
|
|
.pend
|
|
|
|
mul_word_20 .proc
|
|
; AY = AY * 10 * 2
|
|
jsr mul_word_10
|
|
sty P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
ldy P8ZP_SCRATCH_REG
|
|
rts
|
|
.pend
|
|
|
|
mul_byte_25 .proc
|
|
; A=(A*2 + A)*8 + A
|
|
sta P8ZP_SCRATCH_REG
|
|
asl a
|
|
clc
|
|
adc P8ZP_SCRATCH_REG
|
|
asl a
|
|
asl a
|
|
asl a
|
|
clc
|
|
adc P8ZP_SCRATCH_REG
|
|
rts
|
|
.pend
|
|
|
|
mul_word_25 .proc
|
|
; AY = (AY*2 + AY) *8 + AY
|
|
sta P8ZP_SCRATCH_W1
|
|
sty P8ZP_SCRATCH_W1+1
|
|
sta P8ZP_SCRATCH_W2
|
|
sty P8ZP_SCRATCH_W2+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
clc
|
|
adc P8ZP_SCRATCH_W2
|
|
sta P8ZP_SCRATCH_W1
|
|
lda P8ZP_SCRATCH_W1+1
|
|
adc P8ZP_SCRATCH_W2+1
|
|
sta P8ZP_SCRATCH_W1+1
|
|
lda P8ZP_SCRATCH_W1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
clc
|
|
adc P8ZP_SCRATCH_W2
|
|
sta P8ZP_SCRATCH_W1
|
|
lda P8ZP_SCRATCH_W1+1
|
|
adc P8ZP_SCRATCH_W2+1
|
|
tay
|
|
lda P8ZP_SCRATCH_W1
|
|
rts
|
|
.pend
|
|
|
|
mul_byte_40 .proc
|
|
and #7
|
|
tay
|
|
lda _forties,y
|
|
rts
|
|
_forties .byte 0*40, 1*40, 2*40, 3*40, 4*40, 5*40, 6*40, 7*40 & 255
|
|
.pend
|
|
|
|
mul_word_40 .proc
|
|
; AY = (AY*4 + AY)*8
|
|
sta P8ZP_SCRATCH_W1
|
|
sty P8ZP_SCRATCH_W1+1
|
|
sta P8ZP_SCRATCH_W2
|
|
sty P8ZP_SCRATCH_W2+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
asl a
|
|
rol P8ZP_SCRATCH_W1+1
|
|
clc
|
|
adc P8ZP_SCRATCH_W2
|
|
sta P8ZP_SCRATCH_W1
|
|
lda P8ZP_SCRATCH_W1+1
|
|
adc P8ZP_SCRATCH_W2+1
|
|
asl P8ZP_SCRATCH_W1
|
|
rol a
|
|
asl P8ZP_SCRATCH_W1
|
|
rol a
|
|
asl P8ZP_SCRATCH_W1
|
|
rol a
|
|
tay
|
|
lda P8ZP_SCRATCH_W1
|
|
rts
|
|
.pend
|
|
|
|
mul_byte_50 .proc
|
|
and #7
|
|
tay
|
|
lda _fifties, y
|
|
rts
|
|
_fifties .byte 0*50, 1*50, 2*50, 3*50, 4*50, 5*50, 6*50 & 255, 7*50 & 255
|
|
.pend
|
|
|
|
mul_word_50 .proc
|
|
; AY = AY * 25 * 2
|
|
jsr mul_word_25
|
|
sty P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
ldy P8ZP_SCRATCH_REG
|
|
rts
|
|
.pend
|
|
|
|
mul_byte_80 .proc
|
|
and #3
|
|
tay
|
|
lda _eighties, y
|
|
rts
|
|
_eighties .byte 0*80, 1*80, 2*80, 3*80
|
|
.pend
|
|
|
|
mul_word_80 .proc
|
|
; AY = AY * 40 * 2
|
|
jsr mul_word_40
|
|
sty P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
ldy P8ZP_SCRATCH_REG
|
|
rts
|
|
.pend
|
|
|
|
mul_byte_100 .proc
|
|
and #3
|
|
tay
|
|
lda _hundreds, y
|
|
rts
|
|
_hundreds .byte 0*100, 1*100, 2*100, 3*100 & 255
|
|
.pend
|
|
|
|
mul_word_100 .proc
|
|
; AY = AY * 25 * 4
|
|
jsr mul_word_25
|
|
sty P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
ldy P8ZP_SCRATCH_REG
|
|
rts
|
|
.pend
|
|
|
|
mul_word_320 .proc
|
|
; AY = A * 256 + A * 64 (msb in Y doesn't matter)
|
|
sta P8ZP_SCRATCH_B1
|
|
ldy #0
|
|
sty P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
asl a
|
|
rol P8ZP_SCRATCH_REG
|
|
pha
|
|
clc
|
|
lda P8ZP_SCRATCH_B1
|
|
adc P8ZP_SCRATCH_REG
|
|
tay
|
|
pla
|
|
rts
|
|
.pend
|
|
|
|
mul_word_640 .proc
|
|
; AY = (A * 2 * 320) (msb in Y doesn't matter)
|
|
asl a
|
|
jmp mul_word_320
|
|
.pend
|
|
|
|
|
|
; ----------- end optimized multiplications -----------
|
|
|
|
|
|
; support for bit shifting that is too large to be unrolled:
|
|
|
|
lsr_byte_A .proc
|
|
; -- lsr signed byte in A times the value in Y (>1)
|
|
cmp #0
|
|
bpl lsr_ubyte_A
|
|
- sec
|
|
ror a
|
|
dey
|
|
bne -
|
|
rts
|
|
.pend
|
|
|
|
lsr_ubyte_A .proc
|
|
; -- lsr unsigned byte in A times the value in Y (>1)
|
|
- lsr a
|
|
dey
|
|
bne -
|
|
rts
|
|
.pend
|
|
|
|
asl_byte_A .proc
|
|
; -- asl any byte in A times the value in Y (>1)
|
|
- asl a
|
|
dey
|
|
bne -
|
|
rts
|
|
.pend
|
|
|
|
|
|
lsr_word_AY .proc
|
|
; -- lsr signed word in AY times the value in X (>1)
|
|
cpy #0
|
|
bpl lsr_uword_AY
|
|
sty P8ZP_SCRATCH_B1
|
|
_negative sec
|
|
ror P8ZP_SCRATCH_B1
|
|
ror a
|
|
dex
|
|
bne _negative
|
|
ldy P8ZP_SCRATCH_B1
|
|
rts
|
|
.pend
|
|
|
|
lsr_uword_AY .proc
|
|
; -- lsr unsigned word in AY times the value in X (>1)
|
|
sty P8ZP_SCRATCH_B1
|
|
- lsr P8ZP_SCRATCH_B1
|
|
ror a
|
|
dex
|
|
bne -
|
|
ldy P8ZP_SCRATCH_B1
|
|
rts
|
|
.pend
|
|
|
|
asl_word_AY .proc
|
|
; -- asl any word in AY times the value in X (>1)
|
|
sty P8ZP_SCRATCH_B1
|
|
- asl a
|
|
rol P8ZP_SCRATCH_B1
|
|
dex
|
|
bne -
|
|
ldy P8ZP_SCRATCH_B1
|
|
rts
|
|
.pend
|
|
|
|
|
|
square .proc
|
|
; -- calculate square of signed word (actually -255..255) in AY, result in AY
|
|
; routine by Lee Davison, source: http://6502.org/source/integers/square.htm
|
|
; using this routine is a lot faster as doing a regular multiplication (for words)
|
|
;
|
|
; Calculates the 16 bit unsigned integer square of the signed 16 bit integer in
|
|
; Numberl/Numberh. The result is always in the range 0 to 65025 and is held in
|
|
; Squarel/Squareh
|
|
;
|
|
; The maximum input range is only +/-255 and no checking is done to ensure that
|
|
; this is so.
|
|
;
|
|
; This routine is useful if you are trying to draw circles as for any circle
|
|
;
|
|
; x^2+y^2=r^2 where x and y are the co-ordinates of any point on the circle and
|
|
; r is the circle radius
|
|
|
|
numberl = P8ZP_SCRATCH_W1 ; number to square low byte
|
|
numberh = P8ZP_SCRATCH_W1+1 ; number to square high byte
|
|
squarel = P8ZP_SCRATCH_W2 ; square low byte
|
|
squareh = P8ZP_SCRATCH_W2+1 ; square high byte
|
|
tempsq = P8ZP_SCRATCH_B1 ; temp byte for intermediate result
|
|
|
|
sta numberl
|
|
sty numberh
|
|
|
|
lda #$00 ; clear a
|
|
sta squarel ; clear square low byte
|
|
; (no need to clear the high byte, it gets shifted out)
|
|
lda numberl ; get number low byte
|
|
ldx numberh ; get number high byte
|
|
bpl _nonneg ; if +ve don't negate it
|
|
; else do a two's complement
|
|
eor #$ff ; invert
|
|
sec ; +1
|
|
adc #$00 ; and add it
|
|
|
|
_nonneg:
|
|
sta tempsq ; save abs(number)
|
|
ldx #$08 ; set bit count
|
|
|
|
_nextr2bit:
|
|
asl squarel ; low byte *2
|
|
rol squareh ; high byte *2+carry from low
|
|
asl a ; shift number byte
|
|
bcc _nosqadd ; don't do add if c = 0
|
|
tay ; save a
|
|
clc ; clear carry for add
|
|
lda tempsq ; get number
|
|
adc squarel ; add number^2 low byte
|
|
sta squarel ; save number^2 low byte
|
|
lda #$00 ; clear a
|
|
adc squareh ; add number^2 high byte
|
|
sta squareh ; save number^2 high byte
|
|
tya ; get a back
|
|
|
|
_nosqadd:
|
|
dex ; decrement bit count
|
|
bne _nextr2bit ; go do next bit
|
|
|
|
lda squarel
|
|
ldy squareh
|
|
rts
|
|
|
|
.pend
|