2019-07-25 12:55:10 +00:00
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/*
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2019-07-25 15:26:43 +00:00
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* Find greatest common denominator using subtraction-based Euclidian algorithm
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2019-07-25 12:55:10 +00:00
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* See https://en.wikipedia.org/wiki/Euclidean_algorithm
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* Based on facebook post from
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*/
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.pc = $801 "Basic"
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:BasicUpstart(main)
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.pc = $80d "Program"
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2019-07-31 11:47:21 +00:00
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.label print_line_cursor = 6
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.label print_char_cursor = 4
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2019-07-25 12:55:10 +00:00
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main: {
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jsr print_cls
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lda #<$400
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sta print_line_cursor
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lda #>$400
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sta print_line_cursor+1
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lda #2
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sta print_euclid.b
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lda #<$400
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sta print_char_cursor
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lda #>$400
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sta print_char_cursor+1
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lda #$80
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sta print_euclid.a
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jsr print_euclid
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lda print_line_cursor
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sta print_char_cursor
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lda print_line_cursor+1
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sta print_char_cursor+1
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lda #$45
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sta print_euclid.b
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lda #$a9
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sta print_euclid.a
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jsr print_euclid
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lda print_line_cursor
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sta print_char_cursor
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lda print_line_cursor+1
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sta print_char_cursor+1
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lda #$37
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sta print_euclid.b
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lda #$9b
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sta print_euclid.a
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jsr print_euclid
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lda print_line_cursor
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sta print_char_cursor
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lda print_line_cursor+1
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sta print_char_cursor+1
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lda #3
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sta print_euclid.b
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lda #$c7
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sta print_euclid.a
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jsr print_euclid
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lda print_line_cursor
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sta print_char_cursor
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lda print_line_cursor+1
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sta print_char_cursor+1
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lda #$1a
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sta print_euclid.b
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lda #$5b
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sta print_euclid.a
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jsr print_euclid
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lda print_line_cursor
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sta print_char_cursor
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lda print_line_cursor+1
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sta print_char_cursor+1
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lda #$bb
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sta print_euclid.b
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lda #$77
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sta print_euclid.a
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jsr print_euclid
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rts
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}
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// print_euclid(byte zeropage(2) a, byte zeropage(3) b)
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print_euclid: {
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.label b = 3
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.label a = 2
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ldx a
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jsr print_byte
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lda #' '
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jsr print_char
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ldx b
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jsr print_byte
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lda #' '
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jsr print_char
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ldx b
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jsr euclid
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lda euclid.a
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tax
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jsr print_byte
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jsr print_ln
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rts
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}
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// Print a newline
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print_ln: {
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b1:
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lda #$28
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clc
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adc print_line_cursor
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sta print_line_cursor
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bcc !+
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inc print_line_cursor+1
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!:
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lda print_line_cursor+1
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cmp print_char_cursor+1
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bcc b1
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bne !+
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lda print_line_cursor
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cmp print_char_cursor
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bcc b1
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!:
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rts
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}
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// Print a byte as HEX
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// print_byte(byte register(X) b)
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print_byte: {
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txa
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lsr
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lsr
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lsr
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lsr
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tay
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lda print_hextab,y
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jsr print_char
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lda #$f
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axs #0
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lda print_hextab,x
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jsr print_char
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rts
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}
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// Print a single char
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// print_char(byte register(A) ch)
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print_char: {
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ldy #0
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sta (print_char_cursor),y
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inc print_char_cursor
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bne !+
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inc print_char_cursor+1
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!:
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rts
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}
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// euclid(byte zeropage(2) a, byte register(X) b)
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euclid: {
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.label a = 2
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b1:
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cpx a
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bne b2
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rts
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b2:
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cpx a
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bcc b3
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txa
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sec
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sbc a
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tax
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jmp b1
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b3:
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txa
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eor #$ff
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sec
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adc a
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sta a
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jmp b1
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}
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// Clear the screen. Also resets current line/char cursor.
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print_cls: {
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jsr memset
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rts
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}
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// Copies the character c (an unsigned char) to the first num characters of the object pointed to by the argument str.
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memset: {
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.const c = ' '
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.const num = $3e8
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.label str = $400
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.label end = str+num
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2019-07-31 11:47:21 +00:00
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.label dst = 6
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2019-07-25 12:55:10 +00:00
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lda #<str
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sta dst
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lda #>str
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sta dst+1
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b1:
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2019-08-07 09:27:55 +00:00
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lda dst+1
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cmp #>end
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bne b2
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lda dst
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cmp #<end
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bne b2
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rts
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b2:
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2019-07-25 12:55:10 +00:00
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lda #c
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ldy #0
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sta (dst),y
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inc dst
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bne !+
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inc dst+1
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!:
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2019-08-07 09:27:55 +00:00
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jmp b1
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2019-07-25 12:55:10 +00:00
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}
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print_hextab: .text "0123456789abcdef"
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