76 lines
2.1 KiB
C
76 lines
2.1 KiB
C
/* $Id$ */
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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(void)
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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(void)
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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 */
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