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stdlib: Fix unintended change to the random_r implementation

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Commit d5bceac99d24af1131b90027dab267e437b65cd1 changed the sequence
of random numbers.  This was completely unintended.  The statistical
properties of the new sequences are unclear, so restore the old
behavior.

Fixes commit d5bceac99d24af1131b90027dab267e437b65cd1 ("stdlib:
random_r: fix unaligned access in initstate and initstate_r
[BZ ]").

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
This commit is contained in:
Florian Weimer 2025-01-20 21:06:43 +01:00
parent a3131e71cf
commit 33b684e019
1 changed files with 4 additions and 3 deletions

7
stdlib/random_r.c

@ -390,9 +390,10 @@ __random_r (struct random_data *buf, int32_t *result)
int32_t *end_ptr = buf->end_ptr;
uint32_t val;
val = read_state (rptr, 0);
int32_t t = read_state (fptr, 0);
write_state (fptr, 0, t + val);
/* Avoid integer overflow with uint32_t arihmetic. */
val = read_state (fptr, 0);
val += read_state (rptr, 0);
write_state (fptr, 0, val);
/* Chucking least random bit. */
*result = val >> 1;
++fptr;