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93 lines
3.1 KiB
C++
93 lines
3.1 KiB
C++
/*
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* Copyright (C) 2012 The Android Open Source Project
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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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#ifndef MINIKIN_SPARSE_BIT_SET_H
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#define MINIKIN_SPARSE_BIT_SET_H
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#include <stdint.h>
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#include <sys/types.h>
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#include <UniquePtr.h>
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// ---------------------------------------------------------------------------
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namespace android {
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// This is an implementation of a set of integers. It is optimized for
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// values that are somewhat sparse, in the ballpark of a maximum value
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// of thousands to millions. It is particularly efficient when there are
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// large gaps. The motivating example is Unicode coverage of a font, but
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// the abstraction itself is fully general.
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class SparseBitSet {
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public:
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SparseBitSet(): mMaxVal(0) {
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}
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// Clear the set
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void clear();
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// Initialize the set to a new value, represented by ranges. For
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// simplicity, these ranges are arranged as pairs of values,
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// inclusive of start, exclusive of end, laid out in a uint32 array.
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void initFromRanges(const uint32_t* ranges, size_t nRanges);
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// Determine whether the value is included in the set
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bool get(uint32_t ch) const {
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if (ch >= mMaxVal) return false;
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uint32_t *bitmap = &mBitmaps[mIndices[ch >> kLogValuesPerPage]];
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uint32_t index = ch & kPageMask;
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return (bitmap[index >> kLogBitsPerEl] & (kElFirst >> (index & kElMask))) != 0;
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}
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// One more than the maximum value in the set, or zero if empty
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uint32_t length() const {
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return mMaxVal;
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}
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// The next set bit starting at fromIndex, inclusive, or kNotFound
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// if none exists.
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uint32_t nextSetBit(uint32_t fromIndex) const;
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static const uint32_t kNotFound = ~0u;
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private:
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static const int kLogValuesPerPage = 8;
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static const int kPageMask = (1 << kLogValuesPerPage) - 1;
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static const int kLogBytesPerEl = 2;
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static const int kLogBitsPerEl = kLogBytesPerEl + 3;
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static const int kElMask = (1 << kLogBitsPerEl) - 1;
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// invariant: sizeof(element) == (1 << kLogBytesPerEl)
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typedef uint32_t element;
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static const element kElAllOnes = ~((element)0);
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static const element kElFirst = ((element)1) << kElMask;
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static const uint32_t noZeroPage = ~0u;
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static uint32_t calcNumPages(const uint32_t* ranges, size_t nRanges);
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static int CountLeadingZeros(element x);
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uint32_t mMaxVal;
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UniquePtr<uint32_t[]> mIndices;
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UniquePtr<element[]> mBitmaps;
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uint32_t mZeroPageIndex;
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};
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// Note: this thing cannot be used in vectors yet. If that were important, we'd need to
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// make the copy constructor work, and probably set up move traits as well.
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}; // namespace android
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#endif // MINIKIN_SPARSE_BIT_SET_H
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