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/*-
* Public Domain 2008-2014 WiredTiger, Inc.
*
* 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.
*/
#include "wt_internal.h"
/*
* __wt_random --
* Return a 32-bit pseudo-random number.
*
* This is an implementation of George Marsaglia's multiply-with-carry pseudo-
* random number generator. Computationally fast, with reasonable randomness
* properties.
*
* We have to be very careful about races here. Multiple threads can call
* __wt_random concurrently, and it is okay if those concurrent calls get the
* same return value. What is *not* okay is if reading the shared state races
* with an update and uses two different values for m_w or m_z. That could
* result in a value of zero, in which case they would be stuck on zero
* forever. Take local copies of the shared values to avoid this.
*/
uint32_t
__wt_random(void)
{
static uint32_t m_w = 521288629;
static uint32_t m_z = 362436069;
uint32_t w = m_w, z = m_z;
m_z = z = 36969 * (z & 65535) + (z >> 16);
m_w = w = 18000 * (w & 65535) + (w >> 16);
return (z << 16) + (w & 65535);
}
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