Fast constexpr integer power (ipow)
A good optimizing compiler will transform tail-recursive functions to run as fast as imperative code. - SO
see also
- C++ Super Optimization: 1000X Faster - general overview of
constexprusage and optimisation- demo with recursive Fibonacci and prime number
- Fast alternative to pow()
ipow
#include <cstdint>
constexpr int64_t ipow(int64_t base, int exp, int64_t result = 1) {
return exp < 1 ? result : ipow(base*base, exp/2, (exp % 2) ? result*base : result);
}double^int
template <int N>
double power(double x) {
if constexpr (N == 0) return 1.0;
else if constexpr (N == 1) return x;
else return x * power<N - 1>(x);
}
double result = power<3>(x); // computes x^3 at compile time
Written on June 26, 2021, Last update on February 25, 2024
c++
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power
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Fibonacci