ceph/src/seastar/include/seastar/core/bitops.hh

   1 /*
   2  * This file is open source software, licensed to you under the terms
   3  * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
   4  * distributed with this work for additional information regarding copyright
   5  * ownership.  You may not use this file except in compliance with the License.
   6  *
   7  * You may obtain a copy of the License at
   8  *
   9  *   http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing,
  12  * software distributed under the License is distributed on an
  13  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14  * KIND, either express or implied.  See the License for the
  15  * specific language governing permissions and limitations
  16  * under the License.
  17  */
  18 /*
  19  * Copyright (C) 2014 Cloudius Systems, Ltd.
  20  */
  21
  22 #pragma once
  23
  24 #include <limits>
  25 #include <type_traits>
  26 #include <seastar/util/concepts.hh>
  27
  28 namespace seastar {
  29
  30 inline
  31 constexpr unsigned count_leading_zeros(unsigned x) {
  32     return __builtin_clz(x);
  33 }
  34
  35 inline
  36 constexpr unsigned count_leading_zeros(unsigned long x) {
  37     return __builtin_clzl(x);
  38 }
  39
  40 inline
  41 constexpr unsigned count_leading_zeros(unsigned long long x) {
  42     return __builtin_clzll(x);
  43 }
  44
  45 inline
  46 constexpr unsigned count_trailing_zeros(unsigned x) {
  47     return __builtin_ctz(x);
  48 }
  49
  50 inline
  51 constexpr unsigned count_trailing_zeros(unsigned long x) {
  52     return __builtin_ctzl(x);
  53 }
  54
  55 inline
  56 constexpr unsigned count_trailing_zeros(unsigned long long x) {
  57     return __builtin_ctzll(x);
  58 }
  59
  60 template<typename T>
  61 SEASTAR_CONCEPT( requires std::is_integral_v<T> )
  62 inline constexpr unsigned log2ceil(T n) {
  63     if (n == 1) {
  64         return 0;
  65     }
  66     return std::numeric_limits<T>::digits - count_leading_zeros(n - 1);
  67 }
  68
  69 template<typename T>
  70 SEASTAR_CONCEPT( requires std::is_integral_v<T> )
  71 inline constexpr unsigned log2floor(T n) {
  72     return std::numeric_limits<T>::digits - count_leading_zeros(n) - 1;
  73 }
  74
  75 }