From c79050aa44b8836d836c5dd22a383a073c28b74b Mon Sep 17 00:00:00 2001 From: nicoo Date: Wed, 12 Feb 2020 13:42:22 +0100 Subject: Import upstream release 1.3.0 Closes: #951184 --- fuzz/uniform_random.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 fuzz/uniform_random.c (limited to 'fuzz/uniform_random.c') diff --git a/fuzz/uniform_random.c b/fuzz/uniform_random.c new file mode 100644 index 0000000..7711d69 --- /dev/null +++ b/fuzz/uniform_random.c @@ -0,0 +1,56 @@ +/* + * Copyright (c) 2008, Damien Miller + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#include +#include + +uint32_t uniform_random(uint32_t); + +/* + * Calculate a uniformly distributed random number less than upper_bound + * avoiding "modulo bias". + * + * Uniformity is achieved by generating new random numbers until the one + * returned is outside the range [0, 2**32 % upper_bound). This + * guarantees the selected random number will be inside + * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound) + * after reduction modulo upper_bound. + */ +uint32_t +uniform_random(uint32_t upper_bound) +{ + uint32_t r, min; + + if (upper_bound < 2) + return 0; + + /* 2**32 % x == (2**32 - x) % x */ + min = -upper_bound % upper_bound; + + /* + * This could theoretically loop forever but each retry has + * p > 0.5 (worst case, usually far better) of selecting a + * number inside the range we need, so it should rarely need + * to re-roll. + */ + for (;;) { + r = (uint32_t)random(); + if (r >= min) + break; + } + + return r % upper_bound; +} -- cgit v1.2.3