Rand.cpp

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "Rand.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, unsigned int *state, unsigned int *&next, int &left );
unsigned int reloadMT( unsigned int *state, unsigned int *&next, int &left );
unsigned int randomMT( unsigned int *state, unsigned int *&next, int &left );
void fillBufferMT( void *buffer, unsigned int bytes, unsigned int *state, unsigned int *&next, int &left );
float frandomMT( unsigned int *state, unsigned int *&next, int &left );

// Uses global vars
void seedMT( unsigned int seed )
{
        seedMT(seed, _state, _next, _left);
}
unsigned int reloadMT( void )
{
        return reloadMT(_state, _next, _left);
}
unsigned int randomMT( void )
{
        return randomMT(_state, _next, _left);
}
float frandomMT( void )
{
        return frandomMT(_state, _next, _left);
}
void fillBufferMT( void *buffer, unsigned int bytes )
{
        fillBufferMT(buffer, bytes, _state, _next, _left);
}

void seedMT( unsigned int seed, unsigned int *state, unsigned int *&next, int &left )   // Defined in cokus_c.c
{
        (void) next;

        //
        // 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( unsigned int *state, unsigned int *&next, int &left )
{
        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( unsigned int *state, unsigned int *&next, int &left )
{
        unsigned int y;

        if ( --left < 0 )
                return ( reloadMT(state, next, left) );

        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;
}

void fillBufferMT( void *buffer, unsigned int bytes, unsigned int *state, unsigned int *&next, int &left )
{
        unsigned int offset=0;
        unsigned int r;
        while (bytes-offset>=sizeof(r))
        {
                r = randomMT();
                memcpy((char*)buffer+offset, &r, sizeof(r));
                offset+=sizeof(r);
        }

        r = randomMT(state, next, left);
        memcpy((char*)buffer+offset, &r, bytes-offset);
}

float frandomMT( unsigned int *state, unsigned int *&next, int &left )
{
        return ( float ) ( ( double ) randomMT(state, next, left) / 4294967296.0 );
}
RakNetRandom::RakNetRandom()
{
        left=-1;
}
RakNetRandom::~RakNetRandom()
{
}
void RakNetRandom::SeedMT( unsigned int seed )
{
        seedMT(seed, state, next, left);
}

unsigned int RakNetRandom::ReloadMT( void )
{
        return reloadMT(state, next, left);
}

unsigned int RakNetRandom::RandomMT( void )
{
        return randomMT(state, next, left);
}

float RakNetRandom::FrandomMT( void )
{
        return frandomMT(state, next, left);
}

void RakNetRandom::FillBufferMT( void *buffer, unsigned int bytes )
{
        fillBufferMT(buffer, bytes, state, next, left);
}

/*
int main(void)
{
int j;

// you can seed with any uint32, but the best are odds in 0..(2^32 - 1)

seedMT(4357U);

// print the first 2,002 random numbers seven to a line as an example

for(j=0; j<2002; j++)
RAKNET_DEBUG_PRINTF(" %10lu%s", (unsigned int) randomMT(), (j%7)==6 ? "\n" : "");

return(EXIT_SUCCESS);
}

*/