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| author | ache <ache@FreeBSD.org> | 2003-02-03 10:29:47 +0000 |
|---|---|---|
| committer | ache <ache@FreeBSD.org> | 2003-02-03 10:29:47 +0000 |
| commit | ca8622af3cd996c8480ab4187ffaee64b0828724 (patch) | |
| tree | 5e0e2f36b3b1593c0b6d9000642d11425bc0a2a2 /sys/libkern/random.c | |
| parent | 2c36f3e337e908559979be58a51470c7336cab06 (diff) | |
| download | FreeBSD-src-ca8622af3cd996c8480ab4187ffaee64b0828724.zip FreeBSD-src-ca8622af3cd996c8480ab4187ffaee64b0828724.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 'sys/libkern/random.c')
| -rw-r--r-- | sys/libkern/random.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/sys/libkern/random.c b/sys/libkern/random.c index 35ddea1..1145a84 100644 --- a/sys/libkern/random.c +++ b/sys/libkern/random.c @@ -61,11 +61,13 @@ random() * Park and Miller, Communications of the ACM, vol. 31, no. 10, * October 1988, p. 1195. */ - x = randseed; + /* Can't be initialized with 0, so use another value. */ + if ((x = randseed) == 0) + x = 123459876; hi = x / 127773; lo = x % 127773; t = 16807 * lo - 2836 * hi; - if (t <= 0) + if (t < 0) t += 0x7fffffff; randseed = t; return (t); |
