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| author | ache <ache@FreeBSD.org> | 2003-02-03 10:22:12 +0000 |
|---|---|---|
| committer | ache <ache@FreeBSD.org> | 2003-02-03 10:22:12 +0000 |
| commit | 2c36f3e337e908559979be58a51470c7336cab06 (patch) | |
| tree | d0cfc71d1b2ec12652d4f2afb24ec1c659571650 /lib/libc/stdlib | |
| parent | 35939fc6c18bf7f610fb321d5196e77794d86853 (diff) | |
| download | FreeBSD-src-2c36f3e337e908559979be58a51470c7336cab06.zip FreeBSD-src-2c36f3e337e908559979be58a51470c7336cab06.tar.gz | |
Park & Miller PRNG can be safely initialized with any value but 0 and stuck
at 0 as designed. Its BSD adaptation tries to fight it by mapping 0 to
2147483647 after calculation, but this method not works since 2147483647
seed returns to 0 again on the next interation. Instead of after calculation
mapping, map 0 to another value _before_ calculation, so it never stucks.
Diffstat (limited to 'lib/libc/stdlib')
| -rw-r--r-- | lib/libc/stdlib/rand.c | 5 | ||||
| -rw-r--r-- | lib/libc/stdlib/random.c | 5 |
2 files changed, 8 insertions, 2 deletions
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c index 5b81da2..47bb36d 100644 --- a/lib/libc/stdlib/rand.c +++ b/lib/libc/stdlib/rand.c @@ -72,10 +72,13 @@ do_rand(unsigned long *ctx) */ long hi, lo, x; + /* Can't be initialized with 0, so use another value. */ + if (*ctx == 0) + *ctx = 123459876; hi = *ctx / 127773; lo = *ctx % 127773; x = 16807 * lo - 2836 * hi; - if (x <= 0) + if (x < 0) x += 0x7fffffff; return ((*ctx = x) % ((u_long)RAND_MAX + 1)); #endif /* !USE_WEAK_SEEDING */ diff --git a/lib/libc/stdlib/random.c b/lib/libc/stdlib/random.c index b3a1e11..82af94c 100644 --- a/lib/libc/stdlib/random.c +++ b/lib/libc/stdlib/random.c @@ -236,10 +236,13 @@ static inline long good_rand (x) */ long hi, lo; + /* Can't be initialized with 0, so use another value. */ + if (x == 0) + x = 123459876; hi = x / 127773; lo = x % 127773; x = 16807 * lo - 2836 * hi; - if (x <= 0) + if (x < 0) x += 0x7fffffff; return (x); #endif /* !USE_WEAK_SEEDING */ |
