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
constexpr bool
doIsPrime (unsigned p, unsigned d) // p: number to check, d: current divisor
{
return d!=2 ? (p%d!=0) && doIsPrime(p,d-1) // check this and smaller divisors
: (p%2!=0); // end recursion if divisor is 2
}
constexpr bool isPrime (unsigned p)
{
return p < 4 ? !(p<2) // handle special cases
: doIsPrime(p,p/2); // start recursion with divisor from p/2
}