Annotation of sys/lib/libkern/arch/sparc64/random.S, Revision 1.1.1.1
1.1 nbrk 1: /* $OpenBSD: random.S,v 1.2 2001/08/20 20:15:29 jason Exp $ */
2: /* $NetBSD: random.S,v 1.1.1.1 1998/06/20 05:18:14 eeh Exp $ */
3:
4: /*
5: * Copyright (c) 1990,1993 The Regents of the University of California.
6: * All rights reserved.
7: *
8: * Redistribution and use in source and binary forms, with or without
9: * modification, are permitted provided that: (1) source code distributions
10: * retain the above copyright notice and this paragraph in its entirety, (2)
11: * distributions including binary code include the above copyright notice and
12: * this paragraph in its entirety in the documentation or other materials
13: * provided with the distribution, and (3) all advertising materials mentioning
14: * features or use of this software display the following acknowledgement:
15: * ``This product includes software developed by the University of California,
16: * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
17: * the University nor the names of its contributors may be used to endorse
18: * or promote products derived from this software without specific prior
19: * written permission.
20: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
21: * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
22: * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
23: *
24: * Here is a very good random number generator. This implementation is
25: * based on ``Two Fast Implementations of the "Minimal Standard" Random
26: * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990,
27: * Vol 33 No 1. Do NOT modify this code unless you have a very thorough
28: * understanding of the algorithm. It's trickier than you think. If
29: * you do change it, make sure that its 10,000'th invocation returns
30: * 1043618065.
31: *
32: * Here is easier-to-decipher pseudocode:
33: *
34: * p = (16807*seed)<30:0> # e.g., the low 31 bits of the product
35: * q = (16807*seed)<62:31> # e.g., the high 31 bits starting at bit 32
36: * if (p + q < 2^31)
37: * seed = p + q
38: * else
39: * seed = ((p + q) & (2^31 - 1)) + 1
40: * return (seed);
41: *
42: * The result is in (0,2^31), e.g., it's always positive.
43: */
44: #include <machine/asm.h>
45:
46: .data
47: randseed:
48: .long 1
49: .text
50: ENTRY(random)
51: sethi %hi(16807), %o1
52: wr %o1, %lo(16807), %y
53: sethi %hi(randseed), %g1
54: ld [%g1 + %lo(randseed)], %o0
55: andcc %g0, 0, %o2
56: mulscc %o2, %o0, %o2
57: mulscc %o2, %o0, %o2
58: mulscc %o2, %o0, %o2
59: mulscc %o2, %o0, %o2
60: mulscc %o2, %o0, %o2
61: mulscc %o2, %o0, %o2
62: mulscc %o2, %o0, %o2
63: mulscc %o2, %o0, %o2
64: mulscc %o2, %o0, %o2
65: mulscc %o2, %o0, %o2
66: mulscc %o2, %o0, %o2
67: mulscc %o2, %o0, %o2
68: mulscc %o2, %o0, %o2
69: mulscc %o2, %o0, %o2
70: mulscc %o2, %o0, %o2
71: mulscc %o2, %g0, %o2
72: rd %y, %o3
73: srl %o2, 16, %o1
74: set 0xffff, %o4
75: and %o4, %o2, %o0
76: sll %o0, 15, %o0
77: srl %o3, 17, %o3
78: or %o3, %o0, %o0
79: addcc %o0, %o1, %o0
80: bneg 1f
81: sethi %hi(0x7fffffff), %o1
82: retl
83: st %o0, [%g1 + %lo(randseed)]
84: 1:
85: or %o1, %lo(0x7fffffff), %o1
86: add %o0, 1, %o0
87: and %o1, %o0, %o0
88: retl
89: st %o0, [%g1 + %lo(randseed)]
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