libcxx/include/__cxx03/__random/log2.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___RANDOM_LOG2_H
  10 #define _LIBCPP___RANDOM_LOG2_H
  11
  12 #include <__cxx03/__config>
  13 #include <__cxx03/__type_traits/conditional.h>
  14 #include <__cxx03/cstddef>
  15
  16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  17 #  pragma GCC system_header
  18 #endif
  19
  20 _LIBCPP_BEGIN_NAMESPACE_STD
  21
  22 template <class _UIntType, _UIntType _Xp, size_t _Rp>
  23 struct __log2_imp;
  24
  25 template <unsigned long long _Xp, size_t _Rp>
  26 struct __log2_imp<unsigned long long, _Xp, _Rp> {
  27   static const size_t value =
  28       _Xp & ((unsigned long long)(1) << _Rp) ? _Rp : __log2_imp<unsigned long long, _Xp, _Rp - 1>::value;
  29 };
  30
  31 template <unsigned long long _Xp>
  32 struct __log2_imp<unsigned long long, _Xp, 0> {
  33   static const size_t value = 0;
  34 };
  35
  36 template <size_t _Rp>
  37 struct __log2_imp<unsigned long long, 0, _Rp> {
  38   static const size_t value = _Rp + 1;
  39 };
  40
  41 #ifndef _LIBCPP_HAS_NO_INT128
  42
  43 template <__uint128_t _Xp, size_t _Rp>
  44 struct __log2_imp<__uint128_t, _Xp, _Rp> {
  45   static const size_t value =
  46       (_Xp >> 64) ? (64 + __log2_imp<unsigned long long, (_Xp >> 64), 63>::value)
  47                   : __log2_imp<unsigned long long, _Xp, 63>::value;
  48 };
  49
  50 #endif // _LIBCPP_HAS_NO_INT128
  51
  52 template <class _UIntType, _UIntType _Xp>
  53 struct __log2 {
  54   static const size_t value = __log2_imp<
  55 #ifndef _LIBCPP_HAS_NO_INT128
  56       __conditional_t<sizeof(_UIntType) <= sizeof(unsigned long long), unsigned long long, __uint128_t>,
  57 #else
  58       unsigned long long,
  59 #endif // _LIBCPP_HAS_NO_INT128
  60       _Xp,
  61       sizeof(_UIntType) * __CHAR_BIT__ - 1>::value;
  62 };
  63
  64 _LIBCPP_END_NAMESPACE_STD
  65
  66 #endif // _LIBCPP___RANDOM_LOG2_H