diff options
Diffstat (limited to 'lib/libc/stdlib/rand.c')
| -rw-r--r-- | lib/libc/stdlib/rand.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c index 94f6b50..70285bd 100644 --- a/lib/libc/stdlib/rand.c +++ b/lib/libc/stdlib/rand.c @@ -31,6 +31,8 @@ * SUCH DAMAGE. * * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. + * + * $FreeBSD$ */ #if defined(LIBC_SCCS) && !defined(lint) @@ -47,7 +49,31 @@ static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; static int do_rand(unsigned long *ctx) { +#ifdef USE_WEAK_SEEDING +/* + * Historic implementation compatibility. + * The random sequences do not vary much with the seed, + * even with overflowing. + */ return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); +#else /* !USE_WEAK_SEEDING */ +/* + * Compute x = (7^5 * x) mod (2^31 - 1) + * wihout overflowing 31 bits: + * (2^31 - 1) = 127773 * (7^5) + 2836 + * 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. + */ + long hi, lo, x; + + hi = *ctx / 127773; + lo = *ctx % 127773; + x = 16807 * lo - 2836 * hi; + if (x <= 0) + x += 0x7fffffff; + return ((*ctx = x) % ((u_long)RAND_MAX + 1)); +#endif /* !USE_WEAK_SEEDING */ } |
