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authorache <ache@FreeBSD.org>2013-07-03 21:21:54 +0000
committerache <ache@FreeBSD.org>2013-07-03 21:21:54 +0000
commit295fb8ce1a43fcd088b63b8b28a6b34191a4faab (patch)
tree1741a11f1eb25d7ff1fecb14fab8e90d942fec2b /lib
parent9256efca5e1c834cea4f307b2f9a54f095eb1753 (diff)
downloadFreeBSD-src-295fb8ce1a43fcd088b63b8b28a6b34191a4faab.zip
FreeBSD-src-295fb8ce1a43fcd088b63b8b28a6b34191a4faab.tar.gz
1) POSIX requires rand(3) return values to be in the [0, RAND_MAX] range,
but ACM formula we use have internal state (and return value) in the [1, 0x7ffffffe] range, so our RAND_MAX (0x7fffffff) is never reached because it is off by one, zero is not reached too. Correct both RAND_MAX and rand(3) return value, shifting last one to the 0 by 1 subtracted, resulting POSIXed [0, 0x7ffffffd(=new RAND_MAX)] range. 2) Add a checks for not overflowing on too big seeds. It may happens on the machines, where sizeof(unsigned int) > 32 bits. Reviewed by: bde [1] MFC after: 2 weeks
Diffstat (limited to 'lib')
-rw-r--r--lib/libc/stdlib/rand.c20
1 files changed, 16 insertions, 4 deletions
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c
index f9c9b56..676c95e 100644
--- a/lib/libc/stdlib/rand.c
+++ b/lib/libc/stdlib/rand.c
@@ -67,15 +67,15 @@ do_rand(unsigned long *ctx)
*/
long hi, lo, x;
- /* Can't be initialized with 0, so use another value. */
- if (*ctx == 0)
- *ctx = 123459876;
+ /* Must be in [1, 0x7ffffffe] range at this point. */
hi = *ctx / 127773;
lo = *ctx % 127773;
x = 16807 * lo - 2836 * hi;
if (x < 0)
x += 0x7fffffff;
- return ((*ctx = x) % ((u_long)RAND_MAX + 1));
+ *ctx = x;
+ /* Transform to [0, 0x7ffffffd] range. */
+ return (x - 1);
#endif /* !USE_WEAK_SEEDING */
}
@@ -84,6 +84,10 @@ int
rand_r(unsigned int *ctx)
{
u_long val = (u_long) *ctx;
+#ifndef USE_WEAK_SEEDING
+ /* Transform to [1, 0x7ffffffe] range. */
+ val = (val % 0x7ffffffe) + 1;
+#endif
int r = do_rand(&val);
*ctx = (unsigned int) val;
@@ -104,6 +108,10 @@ srand(seed)
u_int seed;
{
next = seed;
+#ifndef USE_WEAK_SEEDING
+ /* Transform to [1, 0x7ffffffe] range. */
+ next = (next % 0x7ffffffe) + 1;
+#endif
}
@@ -125,6 +133,10 @@ sranddev()
mib[0] = CTL_KERN;
mib[1] = KERN_ARND;
sysctl(mib, 2, (void *)&next, &len, NULL, 0);
+#ifndef USE_WEAK_SEEDING
+ /* Transform to [1, 0x7ffffffe] range. */
+ next = (next % 0x7ffffffe) + 1;
+#endif
}
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