cpp/openttd-patchpack/source Files · mersenne.c

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r3303:1bae0f5399a4 2.1 KiB text/x-c Show Annotation Show as Raw Download as Raw

bjarni

(svn r4060) -Codechange: [OSX] made the release target (in os/macosx/Makefile) easier to use since it gives the release disk image the right name automatically
it now uses REV instead of RELEASE, which means RELEASE is not needed to be set manaully anymore
it also automatically adds "-jaguar" when making a build aimed at OSX 10.2 (codenamed jaguar)

/* $Id$ */

#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 */