1/*        $NetBSD: random.S,v 1.5 2014/03/07 20:23:09 nakayama Exp $  */
2
3/*
4 * Copyright (c) 1990,1993 The Regents of the University of California.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that: (1) source code distributions
9 * retain the above copyright notice and this paragraph in its entirety, (2)
10 * distributions including binary code include the above copyright notice and
11 * this paragraph in its entirety in the documentation or other materials
12 * provided with the distribution, and (3) all advertising materials mentioning
13 * features or use of this software display the following acknowledgement:
14 * ``This product includes software developed by the University of California,
15 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
16 * the University nor the names of its contributors may be used to endorse
17 * or promote products derived from this software without specific prior
18 * written permission.
19 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
20 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
21 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
22 *
23 * Here is a very good random number generator.  This implementation is
24 * based on ``Two Fast Implementations of the "Minimal Standard" Random
25 * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990,
26 * Vol 33 No 1.  Do NOT modify this code unless you have a very thorough
27 * understanding of the algorithm.  It's trickier than you think.  If
28 * you do change it, make sure that its 10,000'th invocation returns
29 * 1043618065.
30 *
31 * Here is easier-to-decipher pseudocode:
32 *
33 * p = (16807*seed)<30:0>     # e.g., the low 31 bits of the product
34 * q = (16807*seed)<62:31>    # e.g., the high 31 bits starting at bit 32
35 * if (p + q < 2^31)
36 *        seed = p + q
37 * else
38 *        seed = ((p + q) & (2^31 - 1)) + 1
39 * return (seed);
40 *
41 * The result is in (0,2^31), e.g., it's always positive.
42 */
43#include <machine/asm.h>
44
45          .data
46          .align    4
47randseed:
48          .long     1
49
50          .text
51ENTRY(random)
52          sethi     %hi(16807), %o1
53          wr        %o1, %lo(16807), %y
54#ifdef __PIC__
55          PIC_PROLOGUE(%o5, %o2)
56          set       randseed, %g1
57          ld        [%o5 + %g1], %g1
58          ld        [%g1], %o0
59#else
60          sethi     %hi(randseed), %g1
61          ld        [%g1 + %lo(randseed)], %o0
62#endif
63          andcc     %g0, 0, %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, %o0, %o2
72          mulscc  %o2, %o0, %o2
73          mulscc  %o2, %o0, %o2
74          mulscc  %o2, %o0, %o2
75          mulscc  %o2, %o0, %o2
76          mulscc  %o2, %o0, %o2
77          mulscc  %o2, %o0, %o2
78          mulscc  %o2, %o0, %o2
79          mulscc  %o2, %g0, %o2
80          rd        %y, %o3
81          srl       %o2, 16, %o1
82          set       0xffff, %o4
83          and       %o4, %o2, %o0
84          sll       %o0, 15, %o0
85          srl       %o3, 17, %o3
86          or        %o3, %o0, %o0
87          addcc     %o0, %o1, %o0
88          bneg      1f
89          sethi     %hi(0x7fffffff), %o1
90          retl
91#ifdef __PIC__
92          st        %o0, [%g1]
93#else
94          st        %o0, [%g1 + %lo(randseed)]
95#endif
961:
97          or        %o1, %lo(0x7fffffff), %o1
98          add       %o0, 1, %o0
99          and       %o1, %o0, %o0
100          retl
101#ifdef __PIC__
102          st        %o0, [%g1]
103#else
104          st        %o0, [%g1 + %lo(randseed)]
105#endif
106