src/util/rand_xor.c

   1 /*
   2  * Copyright 2017 Timothy Arceri
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  20  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  21  * SOFTWARE.
  22  *
  23  */
  24
  25 #if defined(__linux__)
  26 #include <sys/file.h>
  27 #include <unistd.h>
  28 #else
  29 #include <time.h>
  30 #endif
  31
  32 #include "rand_xor.h"
  33
  34 /* Super fast random number generator.
  35  *
  36  * This rand_xorshift128plus function by Sebastiano Vigna belongs
  37  * to the public domain.
  38  */
  39 uint64_t
  40 rand_xorshift128plus(uint64_t *seed)
  41 {
  42    uint64_t *s = seed;
  43
  44    uint64_t s1 = s[0];
  45    const uint64_t s0 = s[1];
  46    s[0] = s0;
  47    s1 ^= s1 << 23;
  48    s[1] = s1 ^ s0 ^ (s1 >> 18) ^ (s0 >> 5);
  49
  50    return s[1] + s0;
  51 }
  52
  53 void
  54 s_rand_xorshift128plus(uint64_t *seed, bool randomised_seed)
  55 {
  56    if (!randomised_seed)
  57       goto fixed_seed;
  58
  59 #if defined(__linux__)
  60    int fd = open("/dev/urandom", O_RDONLY);
  61    if (fd < 0)
  62       goto fixed_seed;
  63
  64    size_t seed_size = sizeof(uint64_t) * 2;
  65    if (read(fd, seed, seed_size) != seed_size) {
  66       close(fd);
  67       goto fixed_seed;
  68    }
  69
  70    close(fd);
  71    return;
  72
  73 #else
  74    seed[0] = 0x3bffb83978e24f88;
  75    seed[1] = time(NULL);
  76
  77    return;
  78 #endif
  79
  80 fixed_seed:
  81
  82    /* Fallback to a fixed seed */
  83    seed[0] = 0x3bffb83978e24f88;
  84    seed[1] = 0x9238d5d56c71cd35;
  85 }