Thread: Random Numbers class wrapper (based on Julienne Walker's implementation)

I'm wrapping Prelude's implementation of jsw_rand inside a class. So far this is what I have:

CRand.h

PHP Code:

#ifndef CLASS_RANDOM_GENERATOR_H
#define CLASS_RANDOM_GENERATOR_H

/*
  Random number Class

    - Wrapped around Julienne Walker's implementation of Mersenne Twister's found at
      http://eternallyconfuzzled.com/brain.html, as of July, 18, 2006
    - Slightly altered to accomodate the class implementation
*/

class CRand {
private:
    static unsigned int time_seed();

    static const int N = 624;
    static const int M = 397;
    static const unsigned long A  = 0x9908b0dfUL;
    static const unsigned long U  = 0x80000000UL;
    static const unsigned long L  = 0x7fffffffUL;

public:
    explicit CRand(unsigned long, unsigned long);

    // TODO: void reseed(unsigned long = time_seed());
    // TODO: unsigned long rethrow();
private:

    void seed(unsigned long = time_seed());
   // TODO: unsigned long generate();

    unsigned long low_;
    unsigned long high_;
    unsigned long res_; //holds random

    // internal state (per object)
    unsigned long x[N];
    int next;
};

#endif // CLASS_RANDOM_GENERATOR_H 


CRand.cpp

PHP Code:

#include <climits>
#include <ctime>
#include "crand.h"

CRand::CRand(unsigned long low, unsigned long high): low_(low), high_(high) {
    if(low_ > high_) {
        low_ = high;
        high_ = low;
    }

    if( low_ != high_ ) {
        seed();
        //TODO: res_ = generate();
    } else res_ = low_;
}

unsigned int CRand::time_seed() {
  std::time_t now = std::time(0);
  unsigned char *p = (unsigned char *)&now;
  unsigned seed = 0;
  std::size_t i;

  for (i = 0; i < sizeof now; i++)
    seed = seed * ( UCHAR_MAX + 2U ) + p[i];

  return seed;
}

/* Initialize internal state */
void CRand::seed(unsigned long s) {
  int i;

  x[0] = s & 0xffffffffUL;

  for ( i = 1; i < N; i++ ) {
    x[i] = ( 1812433253UL
      * ( x[i - 1] ^ ( x[i - 1] >> 30 ) ) + i );
    x[i] &= 0xffffffffUL;
  }
} 


I'm about to implement the actual jsw_rand() algorithm into the class. However, I'm afraid I couldn't fully understand the discussion about distribution found at http://eternallyconfuzzled.com/articles/rand.html.

My question is, will it be ok, after using Prelude's algorithm jsw_rand(), to use the modulos operator to bring the resulting long into the range defined by my data members low_ and high_? Or should I instead use the uniform deviation she discusses?

Basically... since I'm having an hard time interpreting the code inside jsw_rand() (and because math is not one of my best attributes) I'm at loss as to which it already provides a distribution safeguard(?). My guess is it doesn't and I should either call it repeatedly or provide a uniform deviation algorithm as she discusses.