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* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <minikin/Buffer.h>
#include <sys/types.h>
#include <cstdint>
#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 {
// 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);
explicit SparseBitSet(BufferReader* reader) : SparseBitSet() { initFromBuffer(reader); }
SparseBitSet(SparseBitSet&&) = default;
SparseBitSet& operator=(SparseBitSet&&) = default;
void writeTo(BufferWriter* writer) const;
// 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;
void initFromRanges(const uint32_t* ranges, size_t nRanges);
void initFromBuffer(BufferReader* reader);
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;
uint32_t mIndicesCount;
const uint16_t* mIndices;
uint32_t mBitmapsCount;
const element* mBitmaps;
uint16_t mZeroPageIndex;
// Owns allocated memory if this class is created from ranges, otherwise these are nullptr.
std::unique_ptr<uint16_t[]> mOwnedIndices;
std::unique_ptr<element[]> mOwnedBitmaps;
// Forbid copy and assign.
SparseBitSet(const SparseBitSet&) = delete;
void operator=(const SparseBitSet&) = delete;
} // namespace minikin