svn commit: r252608 - in head: include lib/libc/stdlib
Andrey A. Chernov
ache at FreeBSD.org
Wed Jul 3 21:21:55 UTC 2013
Author: ache
Date: Wed Jul 3 21:21:54 2013
New Revision: 252608
URL: http://svnweb.freebsd.org/changeset/base/252608
Log:
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
Modified:
head/include/stdlib.h
head/lib/libc/stdlib/rand.c
Modified: head/include/stdlib.h
==============================================================================
--- head/include/stdlib.h Wed Jul 3 21:14:57 2013 (r252607)
+++ head/include/stdlib.h Wed Jul 3 21:21:54 2013 (r252608)
@@ -69,7 +69,7 @@ typedef struct {
#define EXIT_FAILURE 1
#define EXIT_SUCCESS 0
-#define RAND_MAX 0x7fffffff
+#define RAND_MAX 0x7ffffffd
__BEGIN_DECLS
#ifdef _XLOCALE_H_
Modified: head/lib/libc/stdlib/rand.c
==============================================================================
--- head/lib/libc/stdlib/rand.c Wed Jul 3 21:14:57 2013 (r252607)
+++ head/lib/libc/stdlib/rand.c Wed Jul 3 21:21:54 2013 (r252608)
@@ -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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