xref: /frameworks/minikin/libs/minikin/CmapCoverage.cpp

/*
 * Copyright (C) 2013 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.
 */

// Determine coverage of font given its raw "cmap" OpenType table

#define LOG_TAG "Minikin"

#include <vector>
using std::vector;

#include <log/log.h>

#include <minikin/SparseBitSet.h>
#include <minikin/CmapCoverage.h>

namespace minikin {

// These could perhaps be optimized to use __builtin_bswap16 and friends.
static uint32_t readU16(const uint8_t* data, size_t offset) {
    return ((uint32_t)data[offset]) << 8 | ((uint32_t)data[offset + 1]);
}

static uint32_t readU32(const uint8_t* data, size_t offset) {
    return ((uint32_t)data[offset]) << 24 | ((uint32_t)data[offset + 1]) << 16 |
        ((uint32_t)data[offset + 2]) << 8 | ((uint32_t)data[offset + 3]);
}

static void addRange(vector<uint32_t> &coverage, uint32_t start, uint32_t end) {
#ifdef VERBOSE_DEBUG
    ALOGD("adding range %d-%d\n", start, end);
#endif
    if (coverage.empty() || coverage.back() < start) {
        coverage.push_back(start);
        coverage.push_back(end);
    } else {
        coverage.back() = end;
    }
}

// Get the coverage information out of a Format 4 subtable, storing it in the coverage vector
static bool getCoverageFormat4(vector<uint32_t>& coverage, const uint8_t* data, size_t size) {
    const size_t kSegCountOffset = 6;
    const size_t kEndCountOffset = 14;
    const size_t kHeaderSize = 16;
    const size_t kSegmentSize = 8;  // total size of array elements for one segment
    if (kEndCountOffset > size) {
        return false;
    }
    size_t segCount = readU16(data, kSegCountOffset) >> 1;
    if (kHeaderSize + segCount * kSegmentSize > size) {
        return false;
    }
    for (size_t i = 0; i < segCount; i++) {
        uint32_t end = readU16(data, kEndCountOffset + 2 * i);
        uint32_t start = readU16(data, kHeaderSize + 2 * (segCount + i));
        if (end < start) {
            // invalid segment range: size must be positive
            android_errorWriteLog(0x534e4554, "26413177");
            return false;
        }
        uint32_t rangeOffset = readU16(data, kHeaderSize + 2 * (3 * segCount + i));
        if (rangeOffset == 0) {
            uint32_t delta = readU16(data, kHeaderSize + 2 * (2 * segCount + i));
            if (((end + delta) & 0xffff) > end - start) {
                addRange(coverage, start, end + 1);
            } else {
                for (uint32_t j = start; j < end + 1; j++) {
                    if (((j + delta) & 0xffff) != 0) {
                        addRange(coverage, j, j + 1);
                    }
                }
            }
        } else {
            for (uint32_t j = start; j < end + 1; j++) {
                uint32_t actualRangeOffset = kHeaderSize + 6 * segCount + rangeOffset +
                    (i + j - start) * 2;
                if (actualRangeOffset + 2 > size) {
                    // invalid rangeOffset is considered a "warning" by OpenType Sanitizer
                    continue;
                }
                uint32_t glyphId = readU16(data, actualRangeOffset);
                if (glyphId != 0) {
                    addRange(coverage, j, j + 1);
                }
            }
        }
    }
    return true;
}

// Get the coverage information out of a Format 12 subtable, storing it in the coverage vector
static bool getCoverageFormat12(vector<uint32_t>& coverage, const uint8_t* data, size_t size) {
    const size_t kNGroupsOffset = 12;
    const size_t kFirstGroupOffset = 16;
    const size_t kGroupSize = 12;
    const size_t kStartCharCodeOffset = 0;
    const size_t kEndCharCodeOffset = 4;
    const size_t kMaxNGroups = 0xfffffff0 / kGroupSize;  // protection against overflow
    // For all values < kMaxNGroups, kFirstGroupOffset + nGroups * kGroupSize fits in 32 bits.
    if (kFirstGroupOffset > size) {
        return false;
    }
    uint32_t nGroups = readU32(data, kNGroupsOffset);
    if (nGroups >= kMaxNGroups || kFirstGroupOffset + nGroups * kGroupSize > size) {
        android_errorWriteLog(0x534e4554, "25645298");
        return false;
    }
    for (uint32_t i = 0; i < nGroups; i++) {
        uint32_t groupOffset = kFirstGroupOffset + i * kGroupSize;
        uint32_t start = readU32(data, groupOffset + kStartCharCodeOffset);
        uint32_t end = readU32(data, groupOffset + kEndCharCodeOffset);
        if (end < start) {
            // invalid group range: size must be positive
            android_errorWriteLog(0x534e4554, "26413177");
            return false;
        }
        addRange(coverage, start, end + 1);  // file is inclusive, vector is exclusive
    }
    return true;
}

// Lower value has higher priority. 0 for the highest priority table.
// kLowestPriority for unsupported tables.
// This order comes from HarfBuzz's hb-ot-font.cc and needs to be kept in sync with it.
constexpr uint8_t kLowestPriority = 255;
uint8_t getTablePriority(uint16_t platformId, uint16_t encodingId) {
    if (platformId == 3 && encodingId == 10) {
        return 0;
    }
    if (platformId == 0 && encodingId == 6) {
        return 1;
    }
    if (platformId == 0 && encodingId == 4) {
        return 2;
    }
    if (platformId == 3 && encodingId == 1) {
        return 3;
    }
    if (platformId == 0 && encodingId == 3) {
        return 4;
    }
    if (platformId == 0 && encodingId == 2) {
        return 5;
    }
    if (platformId == 0 && encodingId == 1) {
        return 6;
    }
    if (platformId == 0 && encodingId == 0) {
        return 7;
    }
    // Tables other than above are not supported.
    return kLowestPriority;
}

SparseBitSet CmapCoverage::getCoverage(const uint8_t* cmap_data, size_t cmap_size,
        bool* has_cmap_format14_subtable) {
    constexpr size_t kHeaderSize = 4;
    constexpr size_t kNumTablesOffset = 2;
    constexpr size_t kTableSize = 8;
    constexpr size_t kPlatformIdOffset = 0;
    constexpr size_t kEncodingIdOffset = 2;
    constexpr size_t kOffsetOffset = 4;
    constexpr size_t kFormatOffset = 0;
    constexpr uint32_t kInvalidOffset = UINT32_MAX;

    if (kHeaderSize > cmap_size) {
        return SparseBitSet();
    }
    uint32_t numTables = readU16(cmap_data, kNumTablesOffset);
    if (kHeaderSize + numTables * kTableSize > cmap_size) {
        return SparseBitSet();
    }

    uint32_t bestTableOffset = kInvalidOffset;
    uint16_t bestTableFormat = 0;
    uint8_t bestTablePriority = kLowestPriority;
    *has_cmap_format14_subtable = false;
    for (uint32_t i = 0; i < numTables; ++i) {
        const uint32_t tableHeadOffset = kHeaderSize + i * kTableSize;
        const uint16_t platformId = readU16(cmap_data, tableHeadOffset + kPlatformIdOffset);
        const uint16_t encodingId = readU16(cmap_data, tableHeadOffset + kEncodingIdOffset);
        const uint32_t offset = readU32(cmap_data, tableHeadOffset + kOffsetOffset);

        if (offset > cmap_size - 2) {
            continue;  // Invalid table: not enough space to read.
        }
        const uint16_t format = readU16(cmap_data, offset + kFormatOffset);

        if (platformId == 0 /* Unicode */ && encodingId == 5 /* Variation Sequences */) {
            if (!(*has_cmap_format14_subtable) && format == 14) {
                *has_cmap_format14_subtable = true;
            } else {
                // Ignore the (0, 5) table if we have already seen another valid one or it's in a
                // format we don't understand.
            }
        } else {
            uint32_t length;
            uint32_t language;

            if (format == 4) {
                constexpr size_t lengthOffset = 2;
                constexpr size_t languageOffset = 4;
                constexpr size_t minTableSize = languageOffset + 2;
                if (offset > cmap_size - minTableSize) {
                    continue;  // Invalid table: not enough space to read.
                }
                length = readU16(cmap_data, offset + lengthOffset);
                language = readU16(cmap_data, offset + languageOffset);
            } else if (format == 12) {
                constexpr size_t lengthOffset = 4;
                constexpr size_t languageOffset = 8;
                constexpr size_t minTableSize = languageOffset + 4;
                if (offset > cmap_size - minTableSize) {
                    continue;  // Invalid table: not enough space to read.
                }
                length = readU32(cmap_data, offset + lengthOffset);
                language = readU32(cmap_data, offset + languageOffset);
            } else {
                continue;
            }

            if (length > cmap_size - offset) {
                continue;  // Invalid table: table length is larger than whole cmap data size.
            }
            if (language != 0) {
                // Unsupported or invalid table: this is either a subtable for the Macintosh
                // platform (which we don't support), or an invalid subtable since language field
                // should be zero for non-Macintosh subtables.
                continue;
            }
            const uint8_t priority = getTablePriority(platformId, encodingId);
            if (priority < bestTablePriority) {
                bestTableOffset = offset;
                bestTablePriority = priority;
                bestTableFormat = format;
            }
        }
        if (*has_cmap_format14_subtable && bestTablePriority == 0 /* highest priority */) {
            // Already found the highest priority table and variation sequences table. No need to
            // look at remaining tables.
            break;
        }
    }
    if (bestTableOffset == kInvalidOffset) {
        return SparseBitSet();
    }
    const uint8_t* tableData = cmap_data + bestTableOffset;
    const size_t tableSize = cmap_size - bestTableOffset;
    vector<uint32_t> coverageVec;
    bool success;
    if (bestTableFormat == 4) {
        success = getCoverageFormat4(coverageVec, tableData, tableSize);
    } else {
        success = getCoverageFormat12(coverageVec, tableData, tableSize);
    }
    if (success) {
        return SparseBitSet(&coverageVec.front(), coverageVec.size() >> 1);
    } else {
        return SparseBitSet();
    }

}

}  // namespace minikin