flutter_flutter/libs/minikin/SparseBitSet.cpp

/*
 * 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.
 */

#define LOG_TAG "SparseBitSet"

#include <stddef.h>
#include <string.h>

#include <log/log.h>

#include <minikin/SparseBitSet.h>

namespace minikin {

const uint32_t SparseBitSet::kNotFound;

void SparseBitSet::clear() {
    mMaxVal = 0;
    if (mOwnIndicesAndBitmaps) {
        delete[] mIndices;
        delete[] mBitmaps;
        mIndexSize = 0;
        mBitmapSize = 0;
        mOwnIndicesAndBitmaps = false;
    }
}

uint32_t SparseBitSet::calcNumPages(const uint32_t* ranges, size_t nRanges) {
    bool haveZeroPage = false;
    uint32_t nonzeroPageEnd = 0;
    uint32_t nPages = 0;
    for (size_t i = 0; i < nRanges; i++) {
        uint32_t start = ranges[i * 2];
        uint32_t end = ranges[i * 2 + 1];
        uint32_t startPage = start >> kLogValuesPerPage;
        uint32_t endPage = (end - 1) >> kLogValuesPerPage;
        if (startPage >= nonzeroPageEnd) {
            if (startPage > nonzeroPageEnd) {
                if (!haveZeroPage) {
                    haveZeroPage = true;
                    nPages++;
                }
            }
            nPages++;
        }
        nPages += endPage - startPage;
        nonzeroPageEnd = endPage + 1;
    }
    return nPages;
}

void SparseBitSet::initFromRanges(const uint32_t* ranges, size_t nRanges) {
    if (nRanges == 0) {
        clear();
        return;
    }
    mMaxVal = ranges[nRanges * 2 - 1];
    mIndexSize = (mMaxVal + kPageMask) >> kLogValuesPerPage;
    uint32_t* indices = new uint32_t[mIndexSize];
    uint32_t nPages = calcNumPages(ranges, nRanges);
    mBitmapSize = nPages << (kLogValuesPerPage - kLogBitsPerEl);
    element* bitmaps = new element[mBitmapSize];
    mOwnIndicesAndBitmaps = true;
    memset(bitmaps, 0, nPages << (kLogValuesPerPage - 3));
    mZeroPageIndex = noZeroPage;
    uint32_t nonzeroPageEnd = 0;
    uint32_t currentPage = 0;
    for (size_t i = 0; i < nRanges; i++) {
        uint32_t start = ranges[i * 2];
        uint32_t end = ranges[i * 2 + 1];
        LOG_ALWAYS_FATAL_IF(end < start);  // make sure range size is nonnegative
        uint32_t startPage = start >> kLogValuesPerPage;
        uint32_t endPage = (end - 1) >> kLogValuesPerPage;
        if (startPage >= nonzeroPageEnd) {
            if (startPage > nonzeroPageEnd) {
                if (mZeroPageIndex == noZeroPage) {
                    mZeroPageIndex = (currentPage++) << (kLogValuesPerPage - kLogBitsPerEl);
                }
                for (uint32_t j = nonzeroPageEnd; j < startPage; j++) {
                    indices[j] = mZeroPageIndex;
                }
            }
            indices[startPage] = (currentPage++) << (kLogValuesPerPage - kLogBitsPerEl);
        }

        size_t index = ((currentPage - 1) << (kLogValuesPerPage - kLogBitsPerEl)) +
            ((start & kPageMask) >> kLogBitsPerEl);
        size_t nElements = (end - (start & ~kElMask) + kElMask) >> kLogBitsPerEl;
        if (nElements == 1) {
            bitmaps[index] |= (kElAllOnes >> (start & kElMask)) &
                (kElAllOnes << ((~end + 1) & kElMask));
        } else {
            bitmaps[index] |= kElAllOnes >> (start & kElMask);
            for (size_t j = 1; j < nElements - 1; j++) {
                bitmaps[index + j] = kElAllOnes;
            }
            bitmaps[index + nElements - 1] |= kElAllOnes << ((~end + 1) & kElMask);
        }
        for (size_t j = startPage + 1; j < endPage + 1; j++) {
            indices[j] = (currentPage++) << (kLogValuesPerPage - kLogBitsPerEl);
        }
        nonzeroPageEnd = endPage + 1;
    }
    mBitmaps = bitmaps;
    mIndices = indices;
}

struct SparseBitSetHeader {
  uint32_t maxValue;
  uint32_t zeroPageIndex;
  uint32_t indexSize;
  uint32_t bitmapSize;
};

bool SparseBitSet::initFromBuffer(const uint8_t* data, size_t size) {
    // No need to be concerned about endianness here since Intel x86 CPUs are little-endian. ARM
    // CPUs are bi-endian but the endianness is only changeable at reset time and is impossible to
    // change at runtime. Thus incoming data is guaranteed to have the same endianness as when it
    // was created.

    if (data == nullptr || size < sizeof(SparseBitSetHeader)) {
        clear();
        return false;
    }

    // The serialized data starts with SparseBitSetHeader.
    const SparseBitSetHeader* header = reinterpret_cast<const SparseBitSetHeader*>(data);
    mMaxVal = header->maxValue;
    mZeroPageIndex = header->zeroPageIndex;
    mIndexSize = header->indexSize;
    mBitmapSize = header->bitmapSize;

    mOwnIndicesAndBitmaps = false;
    if (mIndexSize == 0 || mBitmapSize == 0 || mMaxVal == 0) {
        const bool isValidEmptyBitSet = (mIndexSize == 0 && mBitmapSize == 0 && mMaxVal == 0);
        if (!isValidEmptyBitSet) {
            clear();
        }
        return isValidEmptyBitSet;
    }

    const size_t indicesSizeInBytes = sizeof(mIndices[0]) * mIndexSize;
    const size_t bitmapsSizeInBytes = sizeof(mBitmaps[0]) * mBitmapSize;
    if (size != sizeof(SparseBitSetHeader) + indicesSizeInBytes + bitmapsSizeInBytes) {
        clear();
        return false;
    }
    data += sizeof(SparseBitSetHeader);
    mIndices = reinterpret_cast<decltype(mIndices)>(data);
    data += indicesSizeInBytes;
    mBitmaps = reinterpret_cast<decltype(mBitmaps)>(data);
    return true;
}

size_t SparseBitSet::writeToBuffer(uint8_t* out) const{
    // See comments in SparseBitSet::initFromBuffer for the data structure.
    const size_t indicesSizeInBytes = sizeof(mIndices[0]) * mIndexSize;
    const size_t bitmapsSizeInBytes = sizeof(mBitmaps[0]) * mBitmapSize;
    size_t necessarySize = sizeof(SparseBitSetHeader) + indicesSizeInBytes + bitmapsSizeInBytes;
    if (out != nullptr) {
        SparseBitSetHeader* header = reinterpret_cast<SparseBitSetHeader*>(out);
        header->maxValue = mMaxVal;
        header->zeroPageIndex = mZeroPageIndex;
        header->indexSize = mIndexSize;
        header->bitmapSize = mBitmapSize;

        out += sizeof(SparseBitSetHeader);
        memcpy(out, mIndices, indicesSizeInBytes);
        out += indicesSizeInBytes;
        memcpy(out, mBitmaps, bitmapsSizeInBytes);
    }
    return necessarySize;
}

int SparseBitSet::CountLeadingZeros(element x) {
    // Note: GCC / clang builtin
    return sizeof(element) <= sizeof(int) ? __builtin_clz(x) : __builtin_clzl(x);
}

uint32_t SparseBitSet::nextSetBit(uint32_t fromIndex) const {
    if (fromIndex >= mMaxVal) {
        return kNotFound;
    }
    uint32_t fromPage = fromIndex >> kLogValuesPerPage;
    const element* bitmap = &mBitmaps[mIndices[fromPage]];
    uint32_t offset = (fromIndex & kPageMask) >> kLogBitsPerEl;
    element e = bitmap[offset] & (kElAllOnes >> (fromIndex & kElMask));
    if (e != 0) {
        return (fromIndex & ~kElMask) + CountLeadingZeros(e);
    }
    for (uint32_t j = offset + 1; j < (1 << (kLogValuesPerPage - kLogBitsPerEl)); j++) {
        e = bitmap[j];
        if (e != 0) {
            return (fromIndex & ~kPageMask) + (j << kLogBitsPerEl) + CountLeadingZeros(e);
        }
    }
    uint32_t maxPage = (mMaxVal + kPageMask) >> kLogValuesPerPage;
    for (uint32_t page = fromPage + 1; page < maxPage; page++) {
        uint32_t index = mIndices[page];
        if (index == mZeroPageIndex) {
            continue;
        }
        bitmap = &mBitmaps[index];
        for (uint32_t j = 0; j < (1 << (kLogValuesPerPage - kLogBitsPerEl)); j++) {
            e = bitmap[j];
            if (e != 0) {
                return (page << kLogValuesPerPage) + (j << kLogBitsPerEl) + CountLeadingZeros(e);
            }
        }
    }
    return kNotFound;
}

}  // namespace minikin