sqrt.h

Go to the documentation of this file.

/*
 * Copyright 2021 MusicScience37 (Kenta Kabashima)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once
 
#include <limits>
#include <type_traits>
 
#include "num_collect/constants/half.h"  // IWYU pragma: keep
#include "num_collect/constants/one.h"   // IWYU pragma: keep
#include "num_collect/constants/zero.h"  // IWYU pragma: keep
 
namespace num_collect::constants {
 
template <typename F,
    std::enable_if_t<std::is_floating_point_v<F>, void*> = nullptr>
constexpr auto sqrt(F x) -> F {
    if (x < zero<F>) {
        return std::numeric_limits<F>::quiet_NaN();
    }
    if ((x > std::numeric_limits<F>::max()) ||
        (x < std::numeric_limits<F>::min())) {
        return x;
    }
 
    constexpr int max_loops = 1000;  // safe guard
    F value = half<F> * (x + one<F>);
    for (int i = 0; i < max_loops; ++i) {
        F next_value = half<F> * (value + x / value);
        if (value == next_value) {
            break;
        }
        value = next_value;
    }
 
    return value;
}
 
template <typename I, std::enable_if_t<std::is_integral_v<I>, void*> = nullptr>
constexpr auto sqrt(I x) -> double {
    return sqrt(static_cast<double>(x));
}
 
}  // namespace num_collect::constants