On Tue, Feb 04, 2003 at 16:28:45 +0300, Andrey A. Chernov wrote:
>
> I'll produce working variant based on your patch...
>
When all done correctly, there is repeated pattern still, so some NSHUFF
drop required too:
1 7 e 4 a 0 7 d 3 a 0 6
See attached patch based on -current sources.
--
Andrey A. Chernov
http://ache.pp.ru/
--- /usr/src/lib/libc/stdlib/rand.c Tue Feb 4 14:24:08 2003
+++ ./rand.c Tue Feb 4 16:40:24 2003
@@ -51,10 +51,8 @@
#include <stdio.h>
#endif /* TEST */
-#define NSHUFF 100 /* to drop part of seed -> 1st value correlation */
-
static int
-do_rand(unsigned long *ctx)
+do_rand(uint32_t *ctx)
{
#ifdef USE_WEAK_SEEDING
/*
@@ -65,24 +63,25 @@
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.
+ * New algorithm derived from
+ * The Laws of Cryptography: Pseudo-random Number Generation
+ * by Neal R. Wagner
+ * http://www.cs.utsa.edu/~wagner/laws/rng.html
+ * which itself is derived from work by Donald E. Knuth.
+ *
+ * This is a linear congruence generator using the equation
+ *
+ * x(n+1) = (k * x(n) + a) mod m
+ *
+ * where m is 2^31 - 1, k is 62089911 and a is 0.
*/
- long hi, lo, x;
+ uint64_t tmp;
/* Can't be initialized with 0, so use another value. */
if (*ctx == 0)
*ctx = 123459876;
- hi = *ctx / 127773;
- lo = *ctx % 127773;
- x = 16807 * lo - 2836 * hi;
- if (x < 0)
- x += 0x7fffffff;
- return ((*ctx = x) % ((u_long)RAND_MAX + 1));
+ tmp = ((uint64_t)*ctx * 62089911) % 2147483647;
+ return ((*ctx = tmp) % ((uint32_t)RAND_MAX + 1));
#endif /* !USE_WEAK_SEEDING */
}
@@ -90,7 +89,7 @@
int
rand_r(unsigned int *ctx)
{
- u_long val = (u_long) *ctx;
+ uint32_t val = (uint32_t)*ctx;
int r = do_rand(&val);
*ctx = (unsigned int) val;
@@ -98,7 +97,7 @@
}
-static u_long next = 1;
+static uint32_t next = 1;
int
rand()
@@ -110,11 +109,7 @@
srand(seed)
u_int seed;
{
- int i;
-
next = seed;
- for (i = 0; i < NSHUFF; i++)
- (void)do_rand(&next);
}
