The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
#include "ifthenelse.hpp"
// primary template for main recursive step
template<int N, int LO=1, int HI=N>
struct Sqrt {
// compute the midpoint, rounded up
static constexpr auto mid = (LO+HI+1)/2;
// search a not too large value in a halved interval
using SubT = IfThenElse<(N<mid*mid),
Sqrt<N,LO,mid-1>,
Sqrt<N,mid,HI>>;
static constexpr auto value = SubT::value;
};
// partial specialization for end of recursion criterion
template<int N, int S>
struct Sqrt<N, S, S> {
static constexpr auto value = S;
};