| /* |
| * 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 <UniquePtr.h> |
| |
| // --------------------------------------------------------------------------- |
| |
| namespace android { |
| |
| // 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: |
| SparseBitSet(): mMaxVal(0) { |
| } |
| |
| // Clear the set |
| void clear(); |
| |
| // 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. |
| void initFromRanges(const uint32_t* ranges, size_t nRanges); |
| |
| // Determine whether the value is included in the set |
| bool get(uint32_t ch) const { |
| if (ch >= mMaxVal) return false; |
| 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: |
| 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 uint32_t noZeroPage = ~0u; |
| |
| static uint32_t calcNumPages(const uint32_t* ranges, size_t nRanges); |
| static int CountLeadingZeros(element x); |
| |
| uint32_t mMaxVal; |
| UniquePtr<uint32_t[]> mIndices; |
| UniquePtr<element[]> mBitmaps; |
| uint32_t mZeroPageIndex; |
| }; |
| |
| // Note: this thing cannot be used in vectors yet. If that were important, we'd need to |
| // make the copy constructor work, and probably set up move traits as well. |
| |
| }; // namespace android |
| |
| #endif // MINIKIN_SPARSE_BIT_SET_H |