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72 lines
2.3 KiB
C++
72 lines
2.3 KiB
C++
// Copyright 2016 The Draco Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// File containing a basic set of bit manipulation utilities used within the
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// Draco library.
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// All functions are defined within its own namespace draco::bits::
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#ifndef DRACO_CORE_BIT_UTILS_H_
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#define DRACO_CORE_BIT_UTILS_H_
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#include <inttypes.h>
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namespace draco {
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namespace bits {
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// Returns the number of '1' bits within the input 32 bit integer.
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inline int CountOnes32(uint32_t n) {
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n -= ((n >> 1) & 0x55555555);
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n = ((n >> 2) & 0x33333333) + (n & 0x33333333);
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return (((n + (n >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
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}
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inline uint32_t ReverseBits32(uint32_t n) {
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n = ((n >> 1) & 0x55555555) | ((n & 0x55555555) << 1);
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n = ((n >> 2) & 0x33333333) | ((n & 0x33333333) << 2);
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n = ((n >> 4) & 0x0F0F0F0F) | ((n & 0x0F0F0F0F) << 4);
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n = ((n >> 8) & 0x00FF00FF) | ((n & 0x00FF00FF) << 8);
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return (n >> 16) | (n << 16);
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}
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// Copies the |bnbits| from the src integer into the |dst| integer using the
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// provided bit offsets |dst_offset| and |src_offset|.
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inline void CopyBits32(uint32_t *dst, int dst_offset, uint32_t src,
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int src_offset, int nbits) {
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const uint32_t mask = (~static_cast<uint32_t>(0)) >> (32 - nbits)
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<< dst_offset;
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*dst = (*dst & (~mask)) | (((src >> src_offset) << dst_offset) & mask);
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}
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// Returns the most location of the most significant bit in the input integer
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// |n|.
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// The funcionality is not defined for |n == 0|.
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inline int MostSignificantBit(uint32_t n) {
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#if defined(__GNUC__)
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return 31 ^ __builtin_clz(n);
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#else
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// TODO(fgalligan): Optimize this code.
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int msb = -1;
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while (n != 0) {
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msb++;
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n >>= 1;
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}
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return msb;
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#endif
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}
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} // namespace bits
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} // namespace draco
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#endif // DRACO_CORE_BIT_UTILS_H_
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