tree 3564ae3b07f4a239ae64c74c06e8e3c97322a97d
parent cfbb93f980cea9d735d0a25c4dd0a4e852512443
author Vincent Bernat <vincent@bernat.im> 1418203897 +0100
committer Willy Tarreau <w@1wt.eu> 1418248018 +0100
encoding latin1

BUG/MEDIUM: sample: fix random number upper-bound

random() will generate a number between 0 and RAND_MAX. POSIX mandates
RAND_MAX to be at least 32767. GNU libc uses (1<<31 - 1) as
RAND_MAX.

In smp_fetch_rand(), a reduction is done with a multiply and shift to
avoid skewing the results. However, the shift was always 32 and hence
the numbers were not distributed uniformly in the specified range. We
fix that by dividing by RAND_MAX+1. gcc is smart enough to turn that
into a shift:

    0x000000000046ecc8 <+40>:    shr    $0x1f,%rax
(cherry picked from commit 1228dc0e7ae4a6b16c0c7f74a28f8e84601b526c)