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improve random number generation by using largest 31-bit prime 

as denominator; regenerate the randtbl[] with new generator

patch provided in lib/22853 by KIHARA Hideto; code actually present
in libkern/random.c since 1994/06/03

matches similar change done in glibc in 1995, and FreeBSD & OpenBSD in 1996
This commit is contained in:
jdolecek 2003-11-26 20:44:40 +00:00
parent 6a23b29f58
commit b02f563aeb
1 changed files with 39 additions and 3 deletions
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42
lib/libc/stdlib/random.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: random.c,v 1.22 2003/08/07 16:43:43 agc Exp $ */
/* $NetBSD: random.c,v 1.23 2003/11/26 20:44:40 jdolecek Exp $ */
/*
* Copyright (c) 1983, 1993
@ -34,7 +34,7 @@
#if 0
static char sccsid[] = "@(#)random.c 8.2 (Berkeley) 5/19/95";
#else
__RCSID("$NetBSD: random.c,v 1.22 2003/08/07 16:43:43 agc Exp $");
__RCSID("$NetBSD: random.c,v 1.23 2003/11/26 20:44:40 jdolecek Exp $");
#endif
#endif /* LIBC_SCCS and not lint */
@ -59,6 +59,8 @@ static long random_unlocked __P((void));
static mutex_t random_mutex = MUTEX_INITIALIZER;
#endif
#define USE_BETTER_RANDOM
/*
* random.c:
*
@ -181,6 +183,19 @@ static const int seps[MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
/* LINTED */
static int randtbl[DEG_3 + 1] = {
TYPE_3,
#ifdef USE_BETTER_RANDOM
0x991539b1, 0x16a5bce3, 0x6774a4cd,
0x3e01511e, 0x4e508aaa, 0x61048c05,
0xf5500617, 0x846b7115, 0x6a19892c,
0x896a97af, 0xdb48f936, 0x14898454,
0x37ffd106, 0xb58bff9c, 0x59e17104,
0xcf918a49, 0x09378c83, 0x52c7a471,
0x8d293ea9, 0x1f4fc301, 0xc3db71be,
0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
0x19edc328, 0x87bf4bdd, 0xc9b240e5,
0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
0xf3bec5da,
#else
0x9a319039, 0x32d9c024, 0x9b663182,
0x5da1f342, 0xde3b81e0, 0xdf0a6fb5,
0xf103bc02, 0x48f340fb, 0x7449e56b,
@ -192,6 +207,7 @@ static int randtbl[DEG_3 + 1] = {
0x36413f93, 0xc622c298, 0xf5a42ab8,
0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
0x27fb47b9,
#endif /* USE_BETTER_RANDOM */
};
/*
@ -249,8 +265,28 @@ srandom_unlocked(x)
state[0] = x;
else {
state[0] = x;
for (i = 1; i < rand_deg; i++)
for (i = 1; i < rand_deg; i++) {
#ifdef USE_BETTER_RANDOM
int x1, hi, lo, t;
/*
* Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
* From "Random number generators: good ones are hard
* to find", Park and Miller, Communications of the ACM,
* vol. 31, no. 10,
* October 1988, p. 1195.
*/
x1 = state[i - 1];
hi = x1 / 127773;
lo = x1 % 127773;
t = 16807 * lo - 2836 * hi;
if (t <= 0)
t += 0x7fffffff;
state[i] = t;
#else
state[i] = 1103515245 * state[i - 1] + 12345;
#endif /* USE_BETTER_RANDOM */
}
fptr = &state[rand_sep];
rptr = &state[0];
for (i = 0; i < 10 * rand_deg; i++)