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/* $Id$ */
/** @file mersenne.cpp */
#include "stdafx.h"
#include "openttd.h"
#ifdef MERSENNE_TWISTER
// Source code for Mersenne Twister.
// A Random number generator with much higher quality random numbers.
#define N (624) // length of _mt_state vector
#define M (397) // a period parameter
#define K (0x9908B0DFU) // a magic constant
#define hiBit(u) ((u) & 0x80000000U) // mask all but highest bit of u
#define loBit(u) ((u) & 0x00000001U) // mask all but lowest bit of u
#define loBits(u) ((u) & 0x7FFFFFFFU) // mask the highest bit of u
#define mixBits(u, v) (hiBit(u)|loBits(v)) // move hi bit of u to hi bit of v
static uint32 _mt_state[N+1]; // _mt_state vector + 1 extra to not violate ANSI C
static uint32 *_mt_next; // _mt_next random value is computed from here
static int _mt_left = -1; // can *_mt_next++ this many times before reloading
void SeedMT(uint32 seed)
{
register uint32 x = (seed | 1U) & 0xFFFFFFFFU, *s = _mt_state;
register int j;
for (_mt_left=0, *s++=x, j=N; --j;
*s++ = (x*=69069U) & 0xFFFFFFFFU);
}
static uint32 ReloadMT(void)
{
register uint32 *p0=_mt_state, *p2=_mt_state+2, *pM=_mt_state+M, s0, s1;
register int j;
if (_mt_left < -1)
SeedMT(4357U);
_mt_left=N-1, _mt_next=_mt_state+1;
for (s0=_mt_state[0], s1=_mt_state[1], j=N-M+1; --j; s0=s1, s1=*p2++)
*p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
for (pM=_mt_state, j=M; --j; s0=s1, s1=*p2++)
*p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
s1=_mt_state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
s1 ^= (s1 >> 11);
s1 ^= (s1 << 7) & 0x9D2C5680U;
s1 ^= (s1 << 15) & 0xEFC60000U;
return(s1 ^ (s1 >> 18));
}
uint32 RandomMT(void)
{
uint32 y;
if (--_mt_left < 0)
return ReloadMT();
y = *_mt_next++;
y ^= (y >> 11);
y ^= (y << 7) & 0x9D2C5680U;
y ^= (y << 15) & 0xEFC60000U;
return y ^ (y >> 18);
}
#else
void SeedMT(uint32 seed) {}
#endif /* MERSENNE_TWISTER */
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