bitops.hh

/*
 * This file is open source software, licensed to you under the terms
 * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
 * distributed with this work for additional information regarding copyright
 * ownership.  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.
 */
/*
 * Copyright (C) 2014 Cloudius Systems, Ltd.
 */

#pragma once

#include <limits>

namespace seastar {

inline
constexpr unsigned count_leading_zeros(unsigned x) {
    return __builtin_clz(x);
}

inline
constexpr unsigned count_leading_zeros(unsigned long x) {
    return __builtin_clzl(x);
}

inline
constexpr unsigned count_leading_zeros(unsigned long long x) {
    return __builtin_clzll(x);
}

inline
constexpr unsigned count_trailing_zeros(unsigned x) {
    return __builtin_ctz(x);
}

inline
constexpr unsigned count_trailing_zeros(unsigned long x) {
    return __builtin_ctzl(x);
}

inline
constexpr unsigned count_trailing_zeros(unsigned long long x) {
    return __builtin_ctzll(x);
}

template<typename T>
//requires stdx::is_integral_v<T>
inline constexpr unsigned log2ceil(T n) {
    if (n == 1) {
        return 0;
    }
    return std::numeric_limits<T>::digits - count_leading_zeros(n - 1);
}

template<typename T>
//requires stdx::is_integral_v<T>
inline constexpr unsigned log2floor(T n) {
    return std::numeric_limits<T>::digits - count_leading_zeros(n) - 1;
}

}