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 <__config> 13 #include <__type_traits/conditional.h> 14 #include <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 67