From 295fb8ce1a43fcd088b63b8b28a6b34191a4faab Mon Sep 17 00:00:00 2001 From: ache Date: Wed, 3 Jul 2013 21:21:54 +0000 Subject: 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 --- lib/libc/stdlib/rand.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) (limited to 'lib') 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 } -- cgit v1.1