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/* $Id$ */

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/** @file mersenne.cpp */

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#include "stdafx.h"

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#include "openttd.h"

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#ifdef MERSENNE_TWISTER

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// Source code for Mersenne Twister.

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// A Random number generator with much higher quality random numbers.

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#define N              (624)                 // length of _mt_state vector

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#define M              (397)                 // a period parameter

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#define K              (0x9908B0DFU)         // a magic constant

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#define hiBit(u)       ((u) & 0x80000000U)   // mask all but highest   bit of u

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#define loBit(u)       ((u) & 0x00000001U)   // mask all but lowest    bit of u

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#define loBits(u)      ((u) & 0x7FFFFFFFU)   // mask     the highest   bit of u

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#define mixBits(u, v)  (hiBit(u)|loBits(v))  // move hi bit of u to hi bit of v

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static uint32   _mt_state[N+1];     // _mt_state vector + 1 extra to not violate ANSI C

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static uint32   *_mt_next;          // _mt_next random value is computed from here

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static int      _mt_left = -1;      // can *_mt_next++ this many times before reloading

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void SeedMT(uint32 seed)

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{

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    register uint32 x = (seed | 1U) & 0xFFFFFFFFU, *s = _mt_state;

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    register int    j;

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    for (_mt_left=0, *s++=x, j=N; --j;

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        *s++ = (x*=69069U) & 0xFFFFFFFFU);

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 }

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static uint32 ReloadMT()

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 {

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    register uint32 *p0=_mt_state, *p2=_mt_state+2, *pM=_mt_state+M, s0, s1;

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    register int    j;

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    if (_mt_left < -1)

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        SeedMT(4357U);

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    _mt_left=N-1, _mt_next=_mt_state+1;

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    for (s0=_mt_state[0], s1=_mt_state[1], j=N-M+1; --j; s0=s1, s1=*p2++)

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        *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

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    for (pM=_mt_state, j=M; --j; s0=s1, s1=*p2++)

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        *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

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    s1=_mt_state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);

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    s1 ^= (s1 >> 11);

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    s1 ^= (s1 <<  7) & 0x9D2C5680U;

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    s1 ^= (s1 << 15) & 0xEFC60000U;

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    return(s1 ^ (s1 >> 18));

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 }

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uint32 RandomMT()

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{

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	uint32 y;

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	if (--_mt_left < 0)

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		return ReloadMT();

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	y  = *_mt_next++;

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	y ^= (y >> 11);

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	y ^= (y <<  7) & 0x9D2C5680U;

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	y ^= (y << 15) & 0xEFC60000U;

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	return y ^ (y >> 18);

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}

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#else

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void SeedMT(uint32 seed) {}

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#endif /* MERSENNE_TWISTER */