//  ============================================================
//
//  factorial.h
//
//  Copyright 2002, Dennis Meilicke and Rene Peralta
//
//  ============================================================
//
//  Description:
//
//  NTTL Implementation of:
//      Product
//      Factorial
//
//  ============================================================
#ifndef __nttl_factorial__
#define __nttl_factorial__


template< class T >
void Product( T *Prod, size_t begin, size_t end ) 
//
//  Description:
//  
//  Compute product = begin * (begin + 1 ) * ... * end
//
//  Notes:
//
//  Since 1000! is around 2500 decimal digits, begin and end are
//  limited to being scalars.  This could be relaxed...  Try
//  parameterizing the begin and end types... That is, consider:
//
//      template< class R, class T >
//      R Product( const T &begin, const T &end )
//
//  This would allow small products of consecutive large numbers
//  to be easily calculated.  Don't know why anyone would need
//  this, but...
//  
{
    *Prod = 1;
    size_t beg;
    for( beg=begin ; beg<=end ; beg++ )
        *Prod *= beg;
}


//  ============================================================


template< class T >
void Factorial( T *Prod, size_t end ) 
{
    Product( Prod, 2, end );
}


#endif