pow_pos_int.h

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/*
 * 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 "num_collect/constants/one.h"   // IWYU pragma: keep
#include "num_collect/constants/two.h"   // IWYU pragma: keep
#include "num_collect/constants/zero.h"  // IWYU pragma: keep
 
namespace num_collect::constants::impl {
 
template <typename T, typename I>
constexpr auto pow_pos_int(T base, I exp) -> T {
    if (exp == zero<I>) {
        return one<T>;
    }
    if (exp == one<I>) {
        return base;
    }
    if (exp == two<I>) {
        return base * base;
    }
    I exp1 = exp / two<I>;
    I exp2 = exp - exp1;
    return pow_pos_int(base, exp1) * pow_pos_int(base, exp2);
}
 
}  // namespace num_collect::constants::impl