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- Credit and thanks to Ladislau Szilagyi. Co-Authored-By: ladislau szilagyi <87603175+laci1953@users.noreply.github.com>
53 lines
894 B
ActionScript
53 lines
894 B
ActionScript
; Xorshift is a class of pseudorandom number generators discovered
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; by George Marsaglia and detailed in his 2003 paper, Xorshift RNGs.
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;
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; 16-bit xorshift pseudorandom number generator by John Metcalf
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; returns hl = pseudorandom number
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; corrupts a
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; generates 16-bit pseudorandom numbers with a period of 65535
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; using the xorshift method:
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; hl ^= hl << 7
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; hl ^= hl >> 9
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; hl ^= hl << 8
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; some alternative shift triplets which also perform well are:
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; 6, 7, 13; 7, 9, 13; 9, 7, 13.
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psect text
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GLOBAL _xrnd, _xrndseed
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_xrnd:
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ld hl,1 ; seed must not be 0
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ld a,h
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rra
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ld a,l
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rra
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xor h
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ld h,a
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ld a,l
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rra
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ld a,h
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rra
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xor l
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ld l,a
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xor h
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ld h,a
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ld (_xrnd+1),hl
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res 7,h ;make-it positive...
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ret
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_xrndseed:
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ld a,r
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ld l,a
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ld a,r
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ld h,a
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or l ; HL must be not NULL
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jr nz,1f
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inc hl
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1:
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ld (_xrnd+1),hl
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ret
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