1 // 2 // Copyright 2016 Pixar 3 // 4 // Licensed under the Apache License, Version 2.0 (the "Apache License") 5 // with the following modification; you may not use this file except in 6 // compliance with the Apache License and the following modification to it: 7 // Section 6. Trademarks. is deleted and replaced with: 8 // 9 // 6. Trademarks. This License does not grant permission to use the trade 10 // names, trademarks, service marks, or product names of the Licensor 11 // and its affiliates, except as required to comply with Section 4(c) of 12 // the License and to reproduce the content of the NOTICE file. 13 // 14 // You may obtain a copy of the Apache License at 15 // 16 // http://www.apache.org/licenses/LICENSE-2.0 17 // 18 // Unless required by applicable law or agreed to in writing, software 19 // distributed under the Apache License with the above modification is 20 // distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 21 // KIND, either express or implied. See the Apache License for the specific 22 // language governing permissions and limitations under the Apache License. 23 // 24 #ifndef PXR_BASE_TF_BIT_UTILS_H 25 #define PXR_BASE_TF_BIT_UTILS_H 26 27 /// \file tf/bitUtils.h 28 /// \ingroup group_tf_BasicMath 29 30 #include "pxr/pxr.h" 31 32 #include <cstddef> 33 #include <type_traits> 34 35 PXR_NAMESPACE_OPEN_SCOPE 36 37 /// Compute the number of bits required to store the given number of values. 38 /// 39 /// Note that the computed result for a number smaller or equal to zero is 40 /// undefined. The input number can be any compile-time constant. 41 /// 42 /// \ingroup group_tf_BasicMath 43 /// \hideinitializer 44 #define TF_BITS_FOR_VALUES(n) \ 45 Tf_NumBits<n-1>::type::value 46 47 template <size_t N, size_t SUM=0, size_t BIT=sizeof(N)*8/2> 48 struct Tf_NumBits 49 { 50 // The result is computed by divide and conquer; for a given word N the 51 // bit at position BIT divides the word in an upper and a lower half. 52 // If the upper half contain any ones, then the result is SUM plus BIT 53 // plus the result for the upper half. If not, the result is SUM plus 54 // the result for the lower half. 55 typedef typename std::conditional<N >= (1ULL<<BIT), 56 Tf_NumBits<(N>>BIT), SUM+BIT, BIT/2>, 57 Tf_NumBits<N, SUM, BIT/2> >::type _func; 58 typedef typename _func::type type; 59 }; 60 61 template <size_t N, size_t SUM> 62 struct Tf_NumBits<N, SUM, 0> 63 { 64 typedef std::integral_constant<size_t, SUM+1> type; 65 }; 66 67 /// Compute the number of bits required to store the given number of (signed) 68 /// enum values. 69 /// 70 /// \note This is intended to be used when storing enum values in a bitfield 71 /// without casting the enum type to an unsigned integer. (At least GCC 72 /// considers enums to be signed and hence wastes one bit when all enumerants 73 /// are non-negative). 74 /// 75 /// \ingroup group_tf_BasicMath 76 /// \hideinitializer 77 #define TF_BITS_FOR_ENUM_VALUES(n) \ 78 (TF_BITS_FOR_VALUES(n) + 1) 79 80 PXR_NAMESPACE_CLOSE_SCOPE 81 82 #endif /* PXR_BASE_TF_BIT_UTILS_H */ 83