/* -*- mode: c++; c-file-style: raknet; tab-always-indent: nil; -*- */
 /**
 * @file 
 * @brief Random Value Generator Implementation 
 *
 * Grabbed by Kevin from http://www.math.keio.ac.jp/~matumoto/cokus.c
 *
 * This is the ``Mersenne Twister'' random number generator MT19937, which
 * generates pseudorandom integers uniformly distributed in 0..(2^32 - 1)
 * starting from any odd seed in 0..(2^32 - 1).  This version is a recode
 * by Shawn Cokus (Cokus@math.washington.edu) on March 8, 1998 of a version by
 * Takuji Nishimura (who had suggestions from Topher Cooper and Marc Rieffel in
 * July-August 1997).
 *
 * Effectiveness of the recoding (on Goedel2.math.washington.edu, a DEC Alpha
 * running OSF/1) using GCC -O3 as a compiler: before recoding: 51.6 sec. to
 * generate 300 million random numbers; after recoding: 24.0 sec. for the same
 * (i.e., 46.5% of original time), so speed is now about 12.5 million random
 * number generations per second on this machine.
 * 
 * According to the URL <http://www.math.keio.ac.jp/~matumoto/emt.html>
 * (and paraphrasing a bit in places), the Mersenne Twister is ``designed
 * with consideration of the flaws of various existing generators,'' has
 * a period of 2^19937 - 1, gives a sequence that is 623-dimensionally
 * equidistributed, and ``has passed many stringent tests, including the
 * die-hard test of G. Marsaglia and the load test of P. Hellekalek and
 * S. Wegenkittl.''  It is efficient in memory usage (typically using 2506
 * to 5012 bytes of static data, depending on data type sizes, and the code
 * is quite short as well).  It generates random numbers in batches of 624
 * at a time, so the caching and pipelining of modern systems is exploited.
 * It is also divide- and mod-free.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Library General Public License as published by
 * the Free Software Foundation (either version 2 of the License or, at your
 * option, any later version). This library is distributed in the hope that
 * it will be useful, but WITHOUT ANY WARRANTY, without even the implied
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 * the GNU Library General Public License for more details.  You should have
 * received a copy of the GNU Library General Public License along with this
 * library; if not, write to the Free Software Foundation, Inc., 59 Temple
 * Place, Suite 330, Boston, MA 02111-1307, USA.
 *
 * It would be nice to CC: <Cokus@math.washington.edu> when you write.
 */

#include <stdio.h>
#include <stdlib.h>

//
// uint32 must be an unsigned integer type capable of holding at least 32
// bits; exactly 32 should be fastest, but 64 is better on an Alpha with
// GCC at -O3 optimization so try your options and see what's best for you
//

//typedef unsigned int uint32;

#define N        (624)       // length of 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 unsigned int state[ N + 1 ];     // state vector + 1 extra to not violate ANSI C
static unsigned int *next;        // next random value is computed from here
static int left = -1; // can *next++ this many times before reloading


void seedMT( unsigned int seed )   // Defined in cokus_c.c
{
	//
	// We initialize state[0..(N-1)] via the generator
	//
	//  x_new = (69069 * x_old) mod 2^32
	//
	// from Line 15 of Table 1, p. 106, Sec. 3.3.4 of Knuth's
	// _The Art of Computer Programming_, Volume 2, 3rd ed.
	//
	// Notes (SJC): I do not know what the initial state requirements
	// of the Mersenne Twister are, but it seems this seeding generator
	// could be better.  It achieves the maximum period for its modulus
	// (2^30) iff x_initial is odd (p. 20-21, Sec. 3.2.1.2, Knuth); if
	// x_initial can be even, you have sequences like 0, 0, 0, ...;
	// 2^31, 2^31, 2^31, ...; 2^30, 2^30, 2^30, ...; 2^29, 2^29 + 2^31,
	// 2^29, 2^29 + 2^31, ..., etc. so I force seed to be odd below.
	//
	// Even if x_initial is odd, if x_initial is 1 mod 4 then
	//
	//  the   lowest bit of x is always 1,
	//  the  next-to-lowest bit of x is always 0,
	//  the 2nd-from-lowest bit of x alternates   ... 0 1 0 1 0 1 0 1 ... ,
	//  the 3rd-from-lowest bit of x 4-cycles   ... 0 1 1 0 0 1 1 0 ... ,
	//  the 4th-from-lowest bit of x has the 8-cycle ... 0 0 0 1 1 1 1 0 ... ,
	//   ...
	//
	// and if x_initial is 3 mod 4 then
	//
	//  the   lowest bit of x is always 1,
	//  the  next-to-lowest bit of x is always 1,
	//  the 2nd-from-lowest bit of x alternates   ... 0 1 0 1 0 1 0 1 ... ,
	//  the 3rd-from-lowest bit of x 4-cycles   ... 0 0 1 1 0 0 1 1 ... ,
	//  the 4th-from-lowest bit of x has the 8-cycle ... 0 0 1 1 1 1 0 0 ... ,
	//   ...
	//
	// The generator's potency (min. s>=0 with (69069-1)^s = 0 mod 2^32) is
	// 16, which seems to be alright by p. 25, Sec. 3.2.1.3 of Knuth.  It
	// also does well in the dimension 2..5 spectral tests, but it could be
	// better in dimension 6 (Line 15, Table 1, p. 106, Sec. 3.3.4, Knuth).
	//
	// Note that the random number user does not see the values generated
	// here directly since reloadMT() will always munge them first, so maybe
	// none of all of this matters.  In fact, the seed values made here could
	// even be extra-special desirable if the Mersenne Twister theory says
	// so-- that's why the only change I made is to restrict to odd seeds.
	//

	register unsigned int x = ( seed | 1U ) & 0xFFFFFFFFU, *s = state;
	register int j;

	for ( left = 0, *s++ = x, j = N; --j;
		*s++ = ( x *= 69069U ) & 0xFFFFFFFFU )

		;
}


unsigned int reloadMT( void )
{
	register unsigned int * p0 = state, *p2 = state + 2, *pM = state + M, s0, s1;
	register int j;

	if ( left < -1 )
		seedMT( 4357U );

	left = N - 1, next = state + 1;

	for ( s0 = state[ 0 ], s1 = state[ 1 ], j = N - M + 1; --j; s0 = s1, s1 = *p2++ )
		* p0++ = *pM++ ^ ( mixBits( s0, s1 ) >> 1 ) ^ ( loBit( s1 ) ? K : 0U );

	for ( pM = state, j = M; --j; s0 = s1, s1 = *p2++ )
		* p0++ = *pM++ ^ ( mixBits( s0, s1 ) >> 1 ) ^ ( loBit( s1 ) ? K : 0U );

	s1 = 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 ) );
}


unsigned int randomMT( void )
{
	unsigned int y;

	if ( --left < 0 )
		return ( reloadMT() );

	y = *next++;

	y ^= ( y >> 11 );

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

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

	return ( y ^ ( y >> 18 ) );

	// This change made so the value returned is in the same range as what rand() returns
	// return(y ^ (y >> 18)) % 32767;
}

float frandomMT( void )
{
	return ( float ) ( ( double ) randomMT() / 4294967296.0 );
}



