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Significantly faster rand() implementation

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LRFLEW 2019-10-07 22:37:34 -05:00 committed by Oliver Schmidt
parent fb260ef17f
commit 3994fee595
1 changed files with 6 additions and 16 deletions
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22
libsrc/common/rand.s
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@ -35,27 +35,17 @@ rand: .dword 1
.code
_rand: clc
lda rand+0 ; SEED *= $01010101
adc rand+1
lda rand+0 ; SEED += $B3
adc #$B3
sta rand+0
adc rand+1 ; SEED *= $01010101
sta rand+1
adc rand+2
sta rand+2
adc rand+3
sta rand+3
clc
lda rand+0 ; SEED += $31415927
adc #$27
sta rand+0
lda rand+1
adc #$59
sta rand+1
lda rand+2
adc #$41
sta rand+2
and #$7f ; Suppress sign bit (make it positive)
tax
lda rand+3
adc #$31
lda rand+2
adc rand+3
sta rand+3
rts ; return bit (16-22,24-31) in (X,A)