| /* |
| * Copyright (C) 2012 The Android Open Source Project |
| * |
| * 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. |
| */ |
| |
| #ifndef MINIKIN_SPARSE_BIT_SET_H |
| #define MINIKIN_SPARSE_BIT_SET_H |
| |
| #include <stdint.h> |
| #include <sys/types.h> |
| |
| #include <memory> |
| |
| // --------------------------------------------------------------------------- |
| |
| namespace minikin { |
| |
| // This is an implementation of a set of integers. It is optimized for |
| // values that are somewhat sparse, in the ballpark of a maximum value |
| // of thousands to millions. It is particularly efficient when there are |
| // large gaps. The motivating example is Unicode coverage of a font, but |
| // the abstraction itself is fully general. |
| class SparseBitSet { |
| public: |
| // Create an empty bit set. |
| SparseBitSet() : mMaxVal(0) {} |
| |
| // Initialize the set to a new value, represented by ranges. For |
| // simplicity, these ranges are arranged as pairs of values, |
| // inclusive of start, exclusive of end, laid out in a uint32 array. |
| SparseBitSet(const uint32_t* ranges, size_t nRanges) : SparseBitSet() { |
| initFromRanges(ranges, nRanges); |
| } |
| |
| SparseBitSet(SparseBitSet&&) = default; |
| SparseBitSet& operator=(SparseBitSet&&) = default; |
| |
| // Determine whether the value is included in the set |
| bool get(uint32_t ch) const { |
| if (ch >= mMaxVal) |
| return false; |
| const uint32_t* bitmap = &mBitmaps[mIndices[ch >> kLogValuesPerPage]]; |
| uint32_t index = ch & kPageMask; |
| return (bitmap[index >> kLogBitsPerEl] & (kElFirst >> (index & kElMask))) != |
| 0; |
| } |
| |
| // One more than the maximum value in the set, or zero if empty |
| uint32_t length() const { return mMaxVal; } |
| |
| // The next set bit starting at fromIndex, inclusive, or kNotFound |
| // if none exists. |
| uint32_t nextSetBit(uint32_t fromIndex) const; |
| |
| static const uint32_t kNotFound = ~0u; |
| |
| private: |
| void initFromRanges(const uint32_t* ranges, size_t nRanges); |
| |
| static const uint32_t kMaximumCapacity = 0xFFFFFF; |
| static const int kLogValuesPerPage = 8; |
| static const int kPageMask = (1 << kLogValuesPerPage) - 1; |
| static const int kLogBytesPerEl = 2; |
| static const int kLogBitsPerEl = kLogBytesPerEl + 3; |
| static const int kElMask = (1 << kLogBitsPerEl) - 1; |
| // invariant: sizeof(element) == (1 << kLogBytesPerEl) |
| typedef uint32_t element; |
| static const element kElAllOnes = ~((element)0); |
| static const element kElFirst = ((element)1) << kElMask; |
| static const uint16_t noZeroPage = 0xFFFF; |
| |
| static uint32_t calcNumPages(const uint32_t* ranges, size_t nRanges); |
| static int CountLeadingZeros(element x); |
| |
| uint32_t mMaxVal; |
| |
| std::unique_ptr<uint16_t[]> mIndices; |
| std::unique_ptr<element[]> mBitmaps; |
| uint16_t mZeroPageIndex; |
| |
| // Forbid copy and assign. |
| SparseBitSet(const SparseBitSet&) = delete; |
| void operator=(const SparseBitSet&) = delete; |
| }; |
| |
| } // namespace minikin |
| |
| #endif // MINIKIN_SPARSE_BIT_SET_H |