sqrt2.hpp

C++ Templates 完全导引范例asics

/* The following code example is taken from the book
 * "C++ Templates - The Complete Guide"
 * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002
 *
 * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include "ifthenelse.hpp"

// primary template for main recursive step
template<int N, int LO=1, int HI=N>
class Sqrt {
  public:
    // compute the midpoint, rounded up
    enum { mid = (LO+HI+1)/2 };

    // search a not too large value in a halved interval
    typedef typename IfThenElse<(N<mid*mid),
                                Sqrt<N,LO,mid-1>,
                                Sqrt<N,mid,HI> >::ResultT
            SubT;
    enum { result = SubT::result };
};

// partial specialization for end of recursion criterion
template<int N, int S>
class Sqrt<N, S, S> {
  public:
    enum { result = S };
};