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 <cstddef> 14 #include <type_traits> 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 { 28 static const size_t value = _Xp & ((unsigned long long)(1) << _Rp) ? _Rp 29 : __log2_imp<unsigned long long, _Xp, _Rp - 1>::value; 30 }; 31 32 template <unsigned long long _Xp> 33 struct __log2_imp<unsigned long long, _Xp, 0> 34 { 35 static const size_t value = 0; 36 }; 37 38 template <size_t _Rp> 39 struct __log2_imp<unsigned long long, 0, _Rp> 40 { 41 static const size_t value = _Rp + 1; 42 }; 43 44 #ifndef _LIBCPP_HAS_NO_INT128 45 46 template <__uint128_t _Xp, size_t _Rp> 47 struct __log2_imp<__uint128_t, _Xp, _Rp> 48 { 49 static const size_t value = (_Xp >> 64) 50 ? (64 + __log2_imp<unsigned long long, (_Xp >> 64), 63>::value) 51 : __log2_imp<unsigned long long, _Xp, 63>::value; 52 }; 53 54 #endif // _LIBCPP_HAS_NO_INT128 55 56 template <class _UIntType, _UIntType _Xp> 57 struct __log2 58 { 59 static const size_t value = __log2_imp< 60 #ifndef _LIBCPP_HAS_NO_INT128 61 typename conditional< 62 sizeof(_UIntType) <= sizeof(unsigned long long), 63 unsigned long long, 64 __uint128_t 65 >::type, 66 #else 67 unsigned long long, 68 #endif // _LIBCPP_HAS_NO_INT128 69 _Xp, sizeof(_UIntType) * __CHAR_BIT__ - 1>::value; 70 }; 71 72 _LIBCPP_END_NAMESPACE_STD 73 74 #endif // _LIBCPP___RANDOM_LOG2_H 75