Thu Jun 8 17:54:00 2000 Jeff Johnston <jjohnstn@cygnus.com>

* libc/stdlib/rand_r.c: New algorithm that meets minimal
        standard.
This commit is contained in:
Jeff Johnston 2000-06-08 21:56:18 +00:00
parent af76c2eed1
commit 518882f3a2
2 changed files with 36 additions and 1 deletions

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@ -1,3 +1,8 @@
Thu Jun 8 17:54:00 2000 Jeff Johnston <jjohnstn@cygnus.com>
* libc/stdlib/rand_r.c: New algorithm that meets minimal
standard.
Fri Jun 2 23:02:11 2000 Christopher Faylor <cgf@cygnus.com>
* libc/include/string.h: Work around problem with strsignal and gdb.

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@ -1,7 +1,37 @@
#include <stdlib.h>
/* Pseudo-random generator based on Minimal Standard by
Lewis, Goodman, and Miller in 1969.
I[j+1] = a*I[j] (mod m)
where a = 16807
m = 2147483647
Using Schrage's algorithm, a*I[j] (mod m) can be rewritten as:
a*(I[j] mod q) - r*{I[j]/q} if >= 0
a*(I[j] mod q) - r*{I[j]/q} + m otherwise
where: {} denotes integer division
q = {m/a} = 127773
r = m (mod a) = 2836
note that the seed value of 0 cannot be used in the calculation as
it results in 0 itself
*/
int
_DEFUN (rand_r, (seed), unsigned int *seed)
{
return (((*seed) = (*seed) * 1103515245 + 12345) & RAND_MAX);
long k;
long s = (long)(*seed);
if (s == 0)
s = 0x12345987;
k = s / 127773;
s = 16807 * (s - k * 127773) - 2836 * k;
if (s < 0)
s += 2147483647;
(*seed) = (unsigned int)s;
return (int)(s & RAND_MAX);
}