1 /*-------------------------------------------------------------------------
2 *
3 * erand48.c
4 *
5 * This file supplies pg_erand48(), pg_lrand48(), and pg_srand48(), which
6 * are just like erand48(), lrand48(), and srand48() except that we use
7 * our own implementation rather than the one provided by the operating
8 * system. We used to test for an operating system version rather than
9 * unconditionally using our own, but (1) some versions of Cygwin have a
10 * buggy erand48() that always returns zero and (2) as of 2011, glibc's
11 * erand48() is strangely coded to be almost-but-not-quite thread-safe,
12 * which doesn't matter for the backend but is important for pgbench.
13 *
14 *
15 * Copyright (c) 1993 Martin Birgmeier
16 * All rights reserved.
17 *
18 * You may redistribute unmodified or modified versions of this source
19 * code provided that the above copyright notice and this and the
20 * following conditions are retained.
21 *
22 * This software is provided ``as is'', and comes with no warranties
23 * of any kind. I shall in no event be liable for anything that happens
24 * to anyone/anything when using this software.
25 *
26 * IDENTIFICATION
27 * src/port/erand48.c
28 *
29 *-------------------------------------------------------------------------
30 */
31
32 #include "c.h"
33
34 #include <math.h>
35
36 #define RAND48_SEED_0 (0x330e)
37 #define RAND48_SEED_1 (0xabcd)
38 #define RAND48_SEED_2 (0x1234)
39 #define RAND48_MULT_0 (0xe66d)
40 #define RAND48_MULT_1 (0xdeec)
41 #define RAND48_MULT_2 (0x0005)
42 #define RAND48_ADD (0x000b)
43
44 static unsigned short _rand48_seed[3] = {
45 RAND48_SEED_0,
46 RAND48_SEED_1,
47 RAND48_SEED_2
48 };
49 static unsigned short _rand48_mult[3] = {
50 RAND48_MULT_0,
51 RAND48_MULT_1,
52 RAND48_MULT_2
53 };
54 static unsigned short _rand48_add = RAND48_ADD;
55
56
57 static void
_dorand48(unsigned short xseed[3])58 _dorand48(unsigned short xseed[3])
59 {
60 unsigned long accu;
61 unsigned short temp[2];
62
63 accu = (unsigned long) _rand48_mult[0] * (unsigned long) xseed[0] +
64 (unsigned long) _rand48_add;
65 temp[0] = (unsigned short) accu; /* lower 16 bits */
66 accu >>= sizeof(unsigned short) * 8;
67 accu += (unsigned long) _rand48_mult[0] * (unsigned long) xseed[1] +
68 (unsigned long) _rand48_mult[1] * (unsigned long) xseed[0];
69 temp[1] = (unsigned short) accu; /* middle 16 bits */
70 accu >>= sizeof(unsigned short) * 8;
71 accu += _rand48_mult[0] * xseed[2] + _rand48_mult[1] * xseed[1] + _rand48_mult[2] * xseed[0];
72 xseed[0] = temp[0];
73 xseed[1] = temp[1];
74 xseed[2] = (unsigned short) accu;
75 }
76
77
78 double
pg_erand48(unsigned short xseed[3])79 pg_erand48(unsigned short xseed[3])
80 {
81 _dorand48(xseed);
82 return ldexp((double) xseed[0], -48) +
83 ldexp((double) xseed[1], -32) +
84 ldexp((double) xseed[2], -16);
85 }
86
87 long
pg_lrand48(void)88 pg_lrand48(void)
89 {
90 _dorand48(_rand48_seed);
91 return ((long) _rand48_seed[2] << 15) + ((long) _rand48_seed[1] >> 1);
92 }
93
94 void
pg_srand48(long seed)95 pg_srand48(long seed)
96 {
97 _rand48_seed[0] = RAND48_SEED_0;
98 _rand48_seed[1] = (unsigned short) seed;
99 _rand48_seed[2] = (unsigned short) (seed >> 16);
100 _rand48_mult[0] = RAND48_MULT_0;
101 _rand48_mult[1] = RAND48_MULT_1;
102 _rand48_mult[2] = RAND48_MULT_2;
103 _rand48_add = RAND48_ADD;
104 }
105