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From http://www.jwz.org/xscreensaver/xscreensaver-5.15.tar.gz
[xscreensaver]
/
hacks
/
images
/
m6502
/
keftal.asm
1
; awfully slow.. be patient
2
3
init:
4
ldx #0
5
stx $0
6
inx
7
stx $2
8
stx $3
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inx
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stx $1
11
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loop:
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lda $2
14
cmp #$20
15
bne notIncF2
16
inc $3
17
lda #0
18
sta $2
19
notIncF2:
20
inc $2
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; CALCULATE START
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lda $2
25
sta $f1
26
lda $2
27
sta $f2
28
jsr multiply
29
30
lda $f4
31
sta $f8
32
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lda $3
34
sta $f1
35
lda $3
36
sta $f2
37
jsr multiply
38
39
; CALCULATE STOP
40
41
lda $f4
42
clc
43
adc $f8
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lsr
46
lsr
47
lsr
48
lsr
49
lsr
50
ldx #0
51
sta ($0,x)
52
inc $0
53
lda $0
54
cmp #$00
55
bne notNextY
56
inc $1
57
lda $1
58
cmp #6
59
beq exit
60
notNextY:
61
jmp loop
62
exit:
63
rts
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65
multiply:
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lda #0
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sta $f4
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sta $f5
69
ldx #8
70
a:asl $f4
71
rol $f5
72
asl $f2
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bcc b
74
clc
75
lda $f4
76
adc $f1
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sta $f4
78
bcc b
79
inc $f5
80
b:dex
81
bne a
82
rts