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extern/gltf-draco/draco/src/draco/core/bit_utils.h
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| // Copyright 2016 The Draco Authors. | |||||
| // | |||||
| // Licensed under the Apache License, Version 2.0 (the "License"); | |||||
| // you may not use this file except in compliance with the License. | |||||
| // You may obtain a copy of the License at | |||||
| // | |||||
| // http://www.apache.org/licenses/LICENSE-2.0 | |||||
| // | |||||
| // Unless required by applicable law or agreed to in writing, software | |||||
| // distributed under the License is distributed on an "AS IS" BASIS, | |||||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |||||
| // See the License for the specific language governing permissions and | |||||
| // limitations under the License. | |||||
| // | |||||
| // File containing a basic set of bit manipulation utilities used within the | |||||
| // Draco library. | |||||
| #ifndef DRACO_CORE_BIT_UTILS_H_ | |||||
| #define DRACO_CORE_BIT_UTILS_H_ | |||||
| #include <inttypes.h> | |||||
| #include <stdint.h> | |||||
| #include <type_traits> | |||||
| #if defined(_MSC_VER) | |||||
| #include <intrin.h> | |||||
| #endif // defined(_MSC_VER) | |||||
| namespace draco { | |||||
| // Returns the number of '1' bits within the input 32 bit integer. | |||||
| inline int CountOneBits32(uint32_t n) { | |||||
| n -= ((n >> 1) & 0x55555555); | |||||
| n = ((n >> 2) & 0x33333333) + (n & 0x33333333); | |||||
| return (((n + (n >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24; | |||||
| } | |||||
| inline uint32_t ReverseBits32(uint32_t n) { | |||||
| n = ((n >> 1) & 0x55555555) | ((n & 0x55555555) << 1); | |||||
| n = ((n >> 2) & 0x33333333) | ((n & 0x33333333) << 2); | |||||
| n = ((n >> 4) & 0x0F0F0F0F) | ((n & 0x0F0F0F0F) << 4); | |||||
| n = ((n >> 8) & 0x00FF00FF) | ((n & 0x00FF00FF) << 8); | |||||
| return (n >> 16) | (n << 16); | |||||
| } | |||||
| // Copies the |nbits| from the src integer into the |dst| integer using the | |||||
| // provided bit offsets |dst_offset| and |src_offset|. | |||||
| inline void CopyBits32(uint32_t *dst, int dst_offset, uint32_t src, | |||||
| int src_offset, int nbits) { | |||||
| const uint32_t mask = (~static_cast<uint32_t>(0)) >> (32 - nbits) | |||||
| << dst_offset; | |||||
| *dst = (*dst & (~mask)) | (((src >> src_offset) << dst_offset) & mask); | |||||
| } | |||||
| // Returns the location of the most significant bit in the input integer |n|. | |||||
| // The functionality is not defined for |n == 0|. | |||||
| inline int MostSignificantBit(uint32_t n) { | |||||
| #if defined(__GNUC__) | |||||
| return 31 ^ __builtin_clz(n); | |||||
| #elif defined(_MSC_VER) | |||||
| unsigned long where; | |||||
| _BitScanReverse(&where, n); | |||||
| return (int)where; | |||||
| #else | |||||
| // TODO(fgalligan): Optimize this code. | |||||
| int msb = -1; | |||||
| while (n != 0) { | |||||
| msb++; | |||||
| n >>= 1; | |||||
| } | |||||
| return msb; | |||||
| #endif | |||||
| } | |||||
| // Helper function that converts signed integer values into unsigned integer | |||||
| // symbols that can be encoded using an entropy encoder. | |||||
| void ConvertSignedIntsToSymbols(const int32_t *in, int in_values, | |||||
| uint32_t *out); | |||||
| // Converts unsigned integer symbols encoded with an entropy encoder back to | |||||
| // signed values. | |||||
| void ConvertSymbolsToSignedInts(const uint32_t *in, int in_values, | |||||
| int32_t *out); | |||||
| // Helper function that converts a single signed integer value into an unsigned | |||||
| // integer symbol that can be encoded using an entropy encoder. | |||||
| template <class IntTypeT> | |||||
| typename std::make_unsigned<IntTypeT>::type ConvertSignedIntToSymbol( | |||||
| IntTypeT val) { | |||||
| typedef typename std::make_unsigned<IntTypeT>::type UnsignedType; | |||||
| static_assert(std::is_integral<IntTypeT>::value, "IntTypeT is not integral."); | |||||
| // Early exit if val is positive. | |||||
| if (val >= 0) { | |||||
| return static_cast<UnsignedType>(val) << 1; | |||||
| } | |||||
| val = -(val + 1); // Map -1 to 0, -2 to -1, etc.. | |||||
| UnsignedType ret = static_cast<UnsignedType>(val); | |||||
| ret <<= 1; | |||||
| ret |= 1; | |||||
| return ret; | |||||
| } | |||||
| // Converts a single unsigned integer symbol encoded with an entropy encoder | |||||
| // back to a signed value. | |||||
| template <class IntTypeT> | |||||
| typename std::make_signed<IntTypeT>::type ConvertSymbolToSignedInt( | |||||
| IntTypeT val) { | |||||
| static_assert(std::is_integral<IntTypeT>::value, "IntTypeT is not integral."); | |||||
| typedef typename std::make_signed<IntTypeT>::type SignedType; | |||||
| const bool is_positive = !static_cast<bool>(val & 1); | |||||
| val >>= 1; | |||||
| if (is_positive) { | |||||
| return static_cast<SignedType>(val); | |||||
| } | |||||
| SignedType ret = static_cast<SignedType>(val); | |||||
| ret = -ret - 1; | |||||
| return ret; | |||||
| } | |||||
| } // namespace draco | |||||
| #endif // DRACO_CORE_BIT_UTILS_H_ | |||||