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For rand(3) and random(3) TYPE_0 drop NSHUFF values right after srand{om}()

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to remove part of seed -> 1st value correlation. Correlation still remains
because of algorithm limits. Note that old algorithm have even stronger
correlation, especially in the lower bits area, but not eye-visible, as
current one.
This commit is contained in:
Andrey A. Chernov 2003-02-04 11:24:08 +00:00
parent 3967e18ad6
commit ddd972a9bd
2 changed files with 15 additions and 6 deletions
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8
lib/libc/stdlib/rand.c
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@ -51,6 +51,8 @@ __FBSDID("$FreeBSD$");
#include <stdio.h>
#endif /* TEST */
#define NSHUFF 100 /* to drop part of seed -> 1st value correlation */
static int
do_rand(unsigned long *ctx)
{
@ -108,7 +110,11 @@ void
srand(seed)
u_int seed;
{
int i;
next = seed;
for (i = 0; i < NSHUFF; i++)
(void)do_rand(&next);
}
@ -137,7 +143,7 @@ sranddev()
unsigned long junk;
gettimeofday(&tv, NULL);
next = (getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk;
srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk);
}
}

13
lib/libc/stdlib/random.c
View File

@ -142,6 +142,8 @@ __FBSDID("$FreeBSD$");
*/
#define MAX_TYPES 5 /* max number of types above */
#define NSHUFF 100 /* to drop part of seed -> 1st value correlation */
static long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
static long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
@ -264,19 +266,20 @@ void
srandom(x)
unsigned long x;
{
long i;
long i, lim;
state[0] = x;
if (rand_type == TYPE_0)
state[0] = x;
lim = NSHUFF;
else {
state[0] = x;
for (i = 1; i < rand_deg; i++)
state[i] = good_rand(state[i - 1]);
fptr = &state[rand_sep];
rptr = &state[0];
for (i = 0; i < 10 * rand_deg; i++)
(void)random();
lim = 10 * rand_deg;
}
for (i = 0; i < lim; i++)
(void)random();
}
/*