/* -*- Mode: c; c-basic-offset: 2 -*-

 *

 * seed.c - Seeding functions

 *

 * This is free and unencumbered software released into the public domain.

 *

 * Anyone is free to copy, modify, publish, use, compile, sell, or

 * distribute this software, either in source code form or as a compiled

 * binary, for any purpose, commercial or non-commercial, and by any

 * means.

 *

 * In jurisdictions that recognize copyright laws, the author or authors

 * of this software dedicate any and all copyright interest in the

 * software to the public domain. We make this dedication for the benefit

 * of the public at large and to the detriment of our heirs and

 * successors. We intend this dedication to be an overt act of

 * relinquishment in perpetuity of all present and future rights to this

 * software under copyright law.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.

 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR

 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,

 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

 * OTHER DEALINGS IN THE SOFTWARE.

 *

 * For more information, please refer to <http://unlicense.org/>

 * 

 */

#ifdef MTWIST_CONFIG

#include <mtwist_config.h>

#endif

#include <stdio.h>

#ifdef HAVE_TIME_H

#include <time.h>

#endif

#ifdef HAVE_UNISTD_H

#include <unistd.h>

#endif

#ifdef HAVE_STDINT_H

#include <stdint.h>

#else

/* pessimistic - use an unsigned long */

typedef unsigned long uint32_t;

#endif

#include <mtwist.h>

#include <mtwist_internal.h>

/**

 * mtwist_seed_from_system:

 * @mt: mt object

 *

 * Get a 32 bit unsigned integer random seed based on system sources

 *

 * Return value: seed with only lower 32 bits valid

 */

unsigned long

mtwist_seed_from_system(mtwist* mt)

{

  /* SOURCE 1: processor clock ticks since process started */

  uint32_t a = (uint32_t)clock();

  /* SOURCE 2: unix time in seconds since epoch */

  uint32_t b = (uint32_t)time(NULL);

  uint32_t c;

#ifdef HAVE_UNISTD_H

  /* SOURCE 3: process ID (on unix) */

  c = getpid();

#else

  c = 0;

#endif

  /* Mix seed sources using public domain code from

   * http://www.burtleburtle.net/bob/c/lookup3.c

   */

#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))

  /* inlined mix(a, b, c) macro */

  a -= c;  a ^= rot(c, 4);  c += b;

  b -= a;  b ^= rot(a, 6);  a += c;

  c -= b;  c ^= rot(b, 8);  b += a;

  a -= c;  a ^= rot(c,16);  c += b;

  b -= a;  b ^= rot(a,19);  /* a += c; */ /* CLANG: not needed because of below */

  c -= b;  c ^= rot(b, 4);  /* b += a; */ /* CLANG: last calculation not needed */

  if(mt->static_system_seed)

    c = MT_STATIC_SEED;

  return (unsigned long)c;

}