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

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.

2 files changed, 15 insertions, 6 deletions

diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c
index 47bb36d..dcc445f 100644
--- a/lib/libc/stdlib/rand.c
+++ b/lib/libc/stdlib/rand.c
@@ -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);
 	}
 }
 
diff --git a/lib/libc/stdlib/random.c b/lib/libc/stdlib/random.c
index 82af94c..64310cd 100644
--- a/lib/libc/stdlib/random.c
+++ b/lib/libc/stdlib/random.c
@@ -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();
 }
 
 /*