//ShortRand.h

#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000

#ifndef ShortRandh
#define ShortRandh

/*
A Pseudo Random Number Generator based on Knuth, Vol 2, p. 27.
Returns shorts uniformly distributed over -32768 to 32767
The numbers always occur in the same sequence (invariable seed).

#include "ShortRand.h"
main() {
  CShortRand SRand;
  for(;;) {
    short i=++SRand;
    WORD  d=++SRand;
  }
}
*/

class CShortRand {
  short i;
  char j,k;
public:
  CShortRand() : j(1), k(4) {}
  operator short()   {return i;}
  short operator++() {return Rand();}
private:
  short Rand() {
    static short y[]={-21161, -8478, 30892,-10216, 16950};
    y[k]+=y[j]; //16 bit 2's complement addition with overflow checking disabled
    if(y[k] >  32767) y[k] = -(32768 - (y[k] & 32767)); //make 16 bit rollover to -/+
    if(y[k] < -32768) y[k] =            y[k] & 32767;
    i=y[k];
    if(--k<0) k=4;
    if(--j<0) j=4;
    return i;
  }
};

#endif //ndef ShortRandh