MT19937 with improved initialization, optimization, and simplification.

mtarcok.h

/*
MT19937 with initialization improved 2002/2/10.
Coded by Takuji Nishimura and Makoto Matsumoto.
Faster version using Shawn Cokus's optimization and
Matthe Bellew's simplification.

Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
All rights reserved.                          

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

  1. Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in the
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  3. The names of its contributors may not be used to endorse or promote 
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html

Modifications to original: Hardcoded period parameters. Implemented minimal
stdint. Removed initialization by array. Removed initialization check. Removed
real versions. Stripped comments and general formatting cleanup. Made state
variables into a struct. Renamed functions to be more consistent. Changed
next_state to use state's counter variable. Inlined next_state inside genrand.
Removed next pointer, only using state counter. Added macro for random doubles
in range [0-1]. Modified TWIST macro for minor speedup. Strict ANSI C.
*/

#ifndef __MTARCOK_H
#define __MTARCOK_H

/* minimal stdint implementation */
typedef signed short int16_t;
typedef unsigned long uint32_t;

/* state struct */
typedef struct {
	uint32_t s[624];
	int16_t i;
} mtstate_t;

/* global state object */
static mtstate_t mt = {{0}, 624};

/* initialize state with single seed. MUST be called before use */
void mt_init( uint32_t s ) {
	int16_t j;
	mt.s[0] = s & 0xffffffffUL;
	for ( j = 1; j < 624; j++ ) {
		mt.s[j] = (1812433253UL * (mt.s[j - 1] ^ (mt.s[j - 1] >> 30)) + j);
		mt.s[j] &= 0xffffffffUL;
	}
	mt.i = 624;
}

#define TWIST( u, v ) ((((u & 0x80000000UL) | (v & 0x7fffffffUL)) >> 1) ^ ((v & 1UL) * 0x9908b0dfUL))
/* random unsigned 32bit integer */
uint32_t mt_rand( void ) {
	uint32_t y;
	/* generate the next state if needed */
	if ( mt.i == 624 ) {
		uint32_t* p = mt.s;
		for ( mt.i = 228; --mt.i; p++ )
			*p = p[397] ^ TWIST( p[0], p[1] );
		for ( mt.i = 397; --mt.i; p++ )
			*p = p[-227] ^ TWIST( p[0], p[1] );
		*p = p[-227] ^ TWIST( p[0], p[0] );
		mt.i = 0;
	}
	y = mt.s[mt.i++];
	y ^= (y >> 11);
	y ^= (y << 7) & 0x9d2c5680UL;
	y ^= (y << 15) & 0xefc60000UL;
	y ^= (y >> 18);
	return y;
}

/* random double [0-1] */
#define mt_random() (mt_rand() * (1.0 / 0xffffffffUL))

#endif /* __MTARCOK_H */