// Pseudo Random Number Generator : generate repeatable sequence of values that
//   appear random by scrambling the bits of a 32-bit integer value.
//
// Interface :
//   PRNG(s) - set starting seed
//   seed(s) - reset seed
//   prng() - generate random value in range [0,UINT_MAX]
//   prng(u) - generate random value in range [0,u]
//   prng(l,u) - generate random value in range [l,u]
//
// Examples : generate random number between 5-21
//   prng() % 17 + 5    values 0-16 + 5 = 5-21
//   prng( 16 ) + 5
//   prng( 5, 21 )

#ifndef __PRNG_H__
#define __PRNG_H__

#include <stdint.h>                 // uint32_t
#include <cassert>                  // assert

class PRNG {
    uint32_t  seed_;    // same results on 32/64-bit architectures
  public:
    PRNG( uint32_t  s = 362436069 ) {
    seed_ = s;                  // set seed
    assert( ("invalid seed", seed_ > 0) );
    }
    void seed( uint32_t  s ) {              // reset seed
    seed_ = s;                  // set seed
    assert( ("invalid seed", seed_ > 0) );
    }
    uint32_t operator()() {             // [0,UINT_MAX]
    seed_ = 36969 * (seed_ & 65535) + (seed_>> 16); // scramble bits
    return seed_;
    }
    uint32_t operator()( uint32_t  u ) {        // [0,u]
    return operator()() % (u + 1);
    }
    uint32_t operator()( uint32_t l, uint32_t u ) { // [l,u]
    assert( ("invalid random range", l < u) );
    return operator()( u - l ) + l;
    }
};

#endif