diff options
Diffstat (limited to 'web/server/h2o/libh2o/deps/brotli/enc/compress_fragment.cc')
| -rw-r--r-- | web/server/h2o/libh2o/deps/brotli/enc/compress_fragment.cc | 693 |
1 files changed, 693 insertions, 0 deletions
diff --git a/web/server/h2o/libh2o/deps/brotli/enc/compress_fragment.cc b/web/server/h2o/libh2o/deps/brotli/enc/compress_fragment.cc new file mode 100644 index 00000000..047d7fe9 --- /dev/null +++ b/web/server/h2o/libh2o/deps/brotli/enc/compress_fragment.cc @@ -0,0 +1,693 @@ +/* Copyright 2015 Google Inc. All Rights Reserved. + + Distributed under MIT license. + See file LICENSE for detail or copy at https://opensource.org/licenses/MIT +*/ + +// Function for fast encoding of an input fragment, independently from the input +// history. This function uses one-pass processing: when we find a backward +// match, we immediately emit the corresponding command and literal codes to +// the bit stream. +// +// Adapted from the CompressFragment() function in +// https://github.com/google/snappy/blob/master/snappy.cc + +#include "./compress_fragment.h" + +#include <algorithm> +#include <cstring> + +#include "./brotli_bit_stream.h" +#include "./entropy_encode.h" +#include "./fast_log.h" +#include "./find_match_length.h" +#include "./port.h" +#include "./write_bits.h" + +namespace brotli { + +// kHashMul32 multiplier has these properties: +// * The multiplier must be odd. Otherwise we may lose the highest bit. +// * No long streaks of 1s or 0s. +// * There is no effort to ensure that it is a prime, the oddity is enough +// for this use. +// * The number has been tuned heuristically against compression benchmarks. +static const uint32_t kHashMul32 = 0x1e35a7bd; + +static inline uint32_t Hash(const uint8_t* p, size_t shift) { + const uint64_t h = (BROTLI_UNALIGNED_LOAD64(p) << 24) * kHashMul32; + return static_cast<uint32_t>(h >> shift); +} + +static inline uint32_t HashBytesAtOffset(uint64_t v, int offset, size_t shift) { + assert(offset >= 0); + assert(offset <= 3); + const uint64_t h = ((v >> (8 * offset)) << 24) * kHashMul32; + return static_cast<uint32_t>(h >> shift); +} + +static inline int IsMatch(const uint8_t* p1, const uint8_t* p2) { + return (BROTLI_UNALIGNED_LOAD32(p1) == BROTLI_UNALIGNED_LOAD32(p2) && + p1[4] == p2[4]); +} + +// Builds a literal prefix code into "depths" and "bits" based on the statistics +// of the "input" string and stores it into the bit stream. +// Note that the prefix code here is built from the pre-LZ77 input, therefore +// we can only approximate the statistics of the actual literal stream. +// Moreover, for long inputs we build a histogram from a sample of the input +// and thus have to assign a non-zero depth for each literal. +void BuildAndStoreLiteralPrefixCode(const uint8_t* input, + const size_t input_size, + uint8_t depths[256], + uint16_t bits[256], + size_t* storage_ix, + uint8_t* storage) { + uint32_t histogram[256] = { 0 }; + size_t histogram_total; + if (input_size < (1 << 15)) { + for (size_t i = 0; i < input_size; ++i) { + ++histogram[input[i]]; + } + histogram_total = input_size; + for (size_t i = 0; i < 256; ++i) { + // We weigh the first 11 samples with weight 3 to account for the + // balancing effect of the LZ77 phase on the histogram. + const uint32_t adjust = 2 * std::min(histogram[i], 11u); + histogram[i] += adjust; + histogram_total += adjust; + } + } else { + static const size_t kSampleRate = 29; + for (size_t i = 0; i < input_size; i += kSampleRate) { + ++histogram[input[i]]; + } + histogram_total = (input_size + kSampleRate - 1) / kSampleRate; + for (size_t i = 0; i < 256; ++i) { + // We add 1 to each population count to avoid 0 bit depths (since this is + // only a sample and we don't know if the symbol appears or not), and we + // weigh the first 11 samples with weight 3 to account for the balancing + // effect of the LZ77 phase on the histogram (more frequent symbols are + // more likely to be in backward references instead as literals). + const uint32_t adjust = 1 + 2 * std::min(histogram[i], 11u); + histogram[i] += adjust; + histogram_total += adjust; + } + } + BuildAndStoreHuffmanTreeFast(histogram, histogram_total, + /* max_bits = */ 8, + depths, bits, storage_ix, storage); +} + +// Builds a command and distance prefix code (each 64 symbols) into "depth" and +// "bits" based on "histogram" and stores it into the bit stream. +void BuildAndStoreCommandPrefixCode(const uint32_t histogram[128], + uint8_t depth[128], uint16_t bits[128], + size_t* storage_ix, uint8_t* storage) { + CreateHuffmanTree(histogram, 64, 15, depth); + CreateHuffmanTree(&histogram[64], 64, 14, &depth[64]); + // We have to jump through a few hoopes here in order to compute + // the command bits because the symbols are in a different order than in + // the full alphabet. This looks complicated, but having the symbols + // in this order in the command bits saves a few branches in the Emit* + // functions. + uint8_t cmd_depth[64]; + uint16_t cmd_bits[64]; + memcpy(cmd_depth, depth, 24); + memcpy(cmd_depth + 24, depth + 40, 8); + memcpy(cmd_depth + 32, depth + 24, 8); + memcpy(cmd_depth + 40, depth + 48, 8); + memcpy(cmd_depth + 48, depth + 32, 8); + memcpy(cmd_depth + 56, depth + 56, 8); + ConvertBitDepthsToSymbols(cmd_depth, 64, cmd_bits); + memcpy(bits, cmd_bits, 48); + memcpy(bits + 24, cmd_bits + 32, 16); + memcpy(bits + 32, cmd_bits + 48, 16); + memcpy(bits + 40, cmd_bits + 24, 16); + memcpy(bits + 48, cmd_bits + 40, 16); + memcpy(bits + 56, cmd_bits + 56, 16); + ConvertBitDepthsToSymbols(&depth[64], 64, &bits[64]); + { + // Create the bit length array for the full command alphabet. + uint8_t cmd_depth[704] = { 0 }; + memcpy(cmd_depth, depth, 8); + memcpy(cmd_depth + 64, depth + 8, 8); + memcpy(cmd_depth + 128, depth + 16, 8); + memcpy(cmd_depth + 192, depth + 24, 8); + memcpy(cmd_depth + 384, depth + 32, 8); + for (size_t i = 0; i < 8; ++i) { + cmd_depth[128 + 8 * i] = depth[40 + i]; + cmd_depth[256 + 8 * i] = depth[48 + i]; + cmd_depth[448 + 8 * i] = depth[56 + i]; + } + StoreHuffmanTree(cmd_depth, 704, storage_ix, storage); + } + StoreHuffmanTree(&depth[64], 64, storage_ix, storage); +} + +// REQUIRES: insertlen < 6210 +inline void EmitInsertLen(size_t insertlen, + const uint8_t depth[128], + const uint16_t bits[128], + uint32_t histo[128], + size_t* storage_ix, + uint8_t* storage) { + if (insertlen < 6) { + const size_t code = insertlen + 40; + WriteBits(depth[code], bits[code], storage_ix, storage); + ++histo[code]; + } else if (insertlen < 130) { + insertlen -= 2; + const uint32_t nbits = Log2FloorNonZero(insertlen) - 1u; + const size_t prefix = insertlen >> nbits; + const size_t inscode = (nbits << 1) + prefix + 42; + WriteBits(depth[inscode], bits[inscode], storage_ix, storage); + WriteBits(nbits, insertlen - (prefix << nbits), storage_ix, storage); + ++histo[inscode]; + } else if (insertlen < 2114) { + insertlen -= 66; + const uint32_t nbits = Log2FloorNonZero(insertlen); + const size_t code = nbits + 50; + WriteBits(depth[code], bits[code], storage_ix, storage); + WriteBits(nbits, insertlen - (1 << nbits), storage_ix, storage); + ++histo[code]; + } else { + WriteBits(depth[61], bits[61], storage_ix, storage); + WriteBits(12, insertlen - 2114, storage_ix, storage); + ++histo[21]; + } +} + +inline void EmitLongInsertLen(size_t insertlen, + const uint8_t depth[128], + const uint16_t bits[128], + uint32_t histo[128], + size_t* storage_ix, + uint8_t* storage) { + if (insertlen < 22594) { + WriteBits(depth[62], bits[62], storage_ix, storage); + WriteBits(14, insertlen - 6210, storage_ix, storage); + ++histo[22]; + } else { + WriteBits(depth[63], bits[63], storage_ix, storage); + WriteBits(24, insertlen - 22594, storage_ix, storage); + ++histo[23]; + } +} + +inline void EmitCopyLen(size_t copylen, + const uint8_t depth[128], + const uint16_t bits[128], + uint32_t histo[128], + size_t* storage_ix, + uint8_t* storage) { + if (copylen < 10) { + WriteBits(depth[copylen + 14], bits[copylen + 14], storage_ix, storage); + ++histo[copylen + 14]; + } else if (copylen < 134) { + copylen -= 6; + const uint32_t nbits = Log2FloorNonZero(copylen) - 1u; + const size_t prefix = copylen >> nbits; + const size_t code = (nbits << 1) + prefix + 20; + WriteBits(depth[code], bits[code], storage_ix, storage); + WriteBits(nbits, copylen - (prefix << nbits), storage_ix, storage); + ++histo[code]; + } else if (copylen < 2118) { + copylen -= 70; + const uint32_t nbits = Log2FloorNonZero(copylen); + const size_t code = nbits + 28; + WriteBits(depth[code], bits[code], storage_ix, storage); + WriteBits(nbits, copylen - (1 << nbits), storage_ix, storage); + ++histo[code]; + } else { + WriteBits(depth[39], bits[39], storage_ix, storage); + WriteBits(24, copylen - 2118, storage_ix, storage); + ++histo[47]; + } +} + +inline void EmitCopyLenLastDistance(size_t copylen, + const uint8_t depth[128], + const uint16_t bits[128], + uint32_t histo[128], + size_t* storage_ix, + uint8_t* storage) { + if (copylen < 12) { + WriteBits(depth[copylen - 4], bits[copylen - 4], storage_ix, storage); + ++histo[copylen - 4]; + } else if (copylen < 72) { + copylen -= 8; + const uint32_t nbits = Log2FloorNonZero(copylen) - 1; + const size_t prefix = copylen >> nbits; + const size_t code = (nbits << 1) + prefix + 4; + WriteBits(depth[code], bits[code], storage_ix, storage); + WriteBits(nbits, copylen - (prefix << nbits), storage_ix, storage); + ++histo[code]; + } else if (copylen < 136) { + copylen -= 8; + const size_t code = (copylen >> 5) + 30; + WriteBits(depth[code], bits[code], storage_ix, storage); + WriteBits(5, copylen & 31, storage_ix, storage); + WriteBits(depth[64], bits[64], storage_ix, storage); + ++histo[code]; + ++histo[64]; + } else if (copylen < 2120) { + copylen -= 72; + const uint32_t nbits = Log2FloorNonZero(copylen); + const size_t code = nbits + 28; + WriteBits(depth[code], bits[code], storage_ix, storage); + WriteBits(nbits, copylen - (1 << nbits), storage_ix, storage); + WriteBits(depth[64], bits[64], storage_ix, storage); + ++histo[code]; + ++histo[64]; + } else { + WriteBits(depth[39], bits[39], storage_ix, storage); + WriteBits(24, copylen - 2120, storage_ix, storage); + WriteBits(depth[64], bits[64], storage_ix, storage); + ++histo[47]; + ++histo[64]; + } +} + +inline void EmitDistance(size_t distance, + const uint8_t depth[128], + const uint16_t bits[128], + uint32_t histo[128], + size_t* storage_ix, uint8_t* storage) { + distance += 3; + const uint32_t nbits = Log2FloorNonZero(distance) - 1u; + const size_t prefix = (distance >> nbits) & 1; + const size_t offset = (2 + prefix) << nbits; + const size_t distcode = 2 * (nbits - 1) + prefix + 80; + WriteBits(depth[distcode], bits[distcode], storage_ix, storage); + WriteBits(nbits, distance - offset, storage_ix, storage); + ++histo[distcode]; +} + +inline void EmitLiterals(const uint8_t* input, const size_t len, + const uint8_t depth[256], const uint16_t bits[256], + size_t* storage_ix, uint8_t* storage) { + for (size_t j = 0; j < len; j++) { + const uint8_t lit = input[j]; + WriteBits(depth[lit], bits[lit], storage_ix, storage); + } +} + +// REQUIRES: len <= 1 << 20. +static void StoreMetaBlockHeader( + size_t len, bool is_uncompressed, size_t* storage_ix, uint8_t* storage) { + // ISLAST + WriteBits(1, 0, storage_ix, storage); + if (len <= (1U << 16)) { + // MNIBBLES is 4 + WriteBits(2, 0, storage_ix, storage); + WriteBits(16, len - 1, storage_ix, storage); + } else { + // MNIBBLES is 5 + WriteBits(2, 1, storage_ix, storage); + WriteBits(20, len - 1, storage_ix, storage); + } + // ISUNCOMPRESSED + WriteBits(1, is_uncompressed, storage_ix, storage); +} + +void UpdateBits(size_t n_bits, + uint32_t bits, + size_t pos, + uint8_t *array) { + while (n_bits > 0) { + size_t byte_pos = pos >> 3; + size_t n_unchanged_bits = pos & 7; + size_t n_changed_bits = std::min(n_bits, 8 - n_unchanged_bits); + size_t total_bits = n_unchanged_bits + n_changed_bits; + uint32_t mask = (~((1 << total_bits) - 1)) | ((1 << n_unchanged_bits) - 1); + uint32_t unchanged_bits = array[byte_pos] & mask; + uint32_t changed_bits = bits & ((1 << n_changed_bits) - 1); + array[byte_pos] = + static_cast<uint8_t>((changed_bits << n_unchanged_bits) | + unchanged_bits); + n_bits -= n_changed_bits; + bits >>= n_changed_bits; + pos += n_changed_bits; + } +} + +void RewindBitPosition(const size_t new_storage_ix, + size_t* storage_ix, uint8_t* storage) { + const size_t bitpos = new_storage_ix & 7; + const size_t mask = (1u << bitpos) - 1; + storage[new_storage_ix >> 3] &= static_cast<uint8_t>(mask); + *storage_ix = new_storage_ix; +} + +bool ShouldMergeBlock(const uint8_t* data, size_t len, const uint8_t* depths) { + size_t histo[256] = { 0 }; + static const size_t kSampleRate = 43; + for (size_t i = 0; i < len; i += kSampleRate) { + ++histo[data[i]]; + } + const size_t total = (len + kSampleRate - 1) / kSampleRate; + double r = (FastLog2(total) + 0.5) * static_cast<double>(total) + 200; + for (size_t i = 0; i < 256; ++i) { + r -= static_cast<double>(histo[i]) * (depths[i] + FastLog2(histo[i])); + } + return r >= 0.0; +} + +inline bool ShouldUseUncompressedMode(const uint8_t* metablock_start, + const uint8_t* next_emit, + const size_t insertlen, + const uint8_t literal_depths[256]) { + const size_t compressed = static_cast<size_t>(next_emit - metablock_start); + if (compressed * 50 > insertlen) { + return false; + } + static const double kAcceptableLossForUncompressibleSpeedup = 0.02; + static const double kMinEntropy = + 8 * (1.0 - kAcceptableLossForUncompressibleSpeedup); + uint32_t sum = 0; + for (int i = 0; i < 256; ++i) { + const uint32_t n = literal_depths[i]; + sum += n << (15 - n); + } + return sum > static_cast<uint32_t>((1 << 15) * kMinEntropy); +} + +void EmitUncompressedMetaBlock(const uint8_t* begin, const uint8_t* end, + const size_t storage_ix_start, + size_t* storage_ix, uint8_t* storage) { + const size_t len = static_cast<size_t>(end - begin); + RewindBitPosition(storage_ix_start, storage_ix, storage); + StoreMetaBlockHeader(len, 1, storage_ix, storage); + *storage_ix = (*storage_ix + 7u) & ~7u; + memcpy(&storage[*storage_ix >> 3], begin, len); + *storage_ix += len << 3; + storage[*storage_ix >> 3] = 0; +} + +void BrotliCompressFragmentFast(const uint8_t* input, size_t input_size, + bool is_last, + int* table, size_t table_size, + uint8_t cmd_depth[128], uint16_t cmd_bits[128], + size_t* cmd_code_numbits, uint8_t* cmd_code, + size_t* storage_ix, uint8_t* storage) { + if (input_size == 0) { + assert(is_last); + WriteBits(1, 1, storage_ix, storage); // islast + WriteBits(1, 1, storage_ix, storage); // isempty + *storage_ix = (*storage_ix + 7u) & ~7u; + return; + } + + // "next_emit" is a pointer to the first byte that is not covered by a + // previous copy. Bytes between "next_emit" and the start of the next copy or + // the end of the input will be emitted as literal bytes. + const uint8_t* next_emit = input; + // Save the start of the first block for position and distance computations. + const uint8_t* base_ip = input; + + static const size_t kFirstBlockSize = 3 << 15; + static const size_t kMergeBlockSize = 1 << 16; + + const uint8_t* metablock_start = input; + size_t block_size = std::min(input_size, kFirstBlockSize); + size_t total_block_size = block_size; + // Save the bit position of the MLEN field of the meta-block header, so that + // we can update it later if we decide to extend this meta-block. + size_t mlen_storage_ix = *storage_ix + 3; + StoreMetaBlockHeader(block_size, 0, storage_ix, storage); + // No block splits, no contexts. + WriteBits(13, 0, storage_ix, storage); + + uint8_t lit_depth[256] = { 0 }; + uint16_t lit_bits[256] = { 0 }; + BuildAndStoreLiteralPrefixCode(input, block_size, lit_depth, lit_bits, + storage_ix, storage); + + // Store the pre-compressed command and distance prefix codes. + for (size_t i = 0; i + 7 < *cmd_code_numbits; i += 8) { + WriteBits(8, cmd_code[i >> 3], storage_ix, storage); + } + WriteBits(*cmd_code_numbits & 7, cmd_code[*cmd_code_numbits >> 3], + storage_ix, storage); + + emit_commands: + // Initialize the command and distance histograms. We will gather + // statistics of command and distance codes during the processing + // of this block and use it to update the command and distance + // prefix codes for the next block. + uint32_t cmd_histo[128] = { + 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 0, 0, 0, 0, + }; + + // "ip" is the input pointer. + const uint8_t* ip = input; + assert(table_size); + assert(table_size <= (1u << 31)); + assert((table_size & (table_size - 1)) == 0); // table must be power of two + const size_t shift = 64u - Log2FloorNonZero(table_size); + assert(static_cast<size_t>(0xffffffffffffffffU >> shift) == table_size - 1); + const uint8_t* ip_end = input + block_size; + + int last_distance = -1; + const size_t kInputMarginBytes = 16; + const size_t kMinMatchLen = 5; + if (PREDICT_TRUE(block_size >= kInputMarginBytes)) { + // For the last block, we need to keep a 16 bytes margin so that we can be + // sure that all distances are at most window size - 16. + // For all other blocks, we only need to keep a margin of 5 bytes so that + // we don't go over the block size with a copy. + const size_t len_limit = std::min(block_size - kMinMatchLen, + input_size - kInputMarginBytes); + const uint8_t* ip_limit = input + len_limit; + + for (uint32_t next_hash = Hash(++ip, shift); ; ) { + assert(next_emit < ip); + // Step 1: Scan forward in the input looking for a 5-byte-long match. + // If we get close to exhausting the input then goto emit_remainder. + // + // Heuristic match skipping: If 32 bytes are scanned with no matches + // found, start looking only at every other byte. If 32 more bytes are + // scanned, look at every third byte, etc.. When a match is found, + // immediately go back to looking at every byte. This is a small loss + // (~5% performance, ~0.1% density) for compressible data due to more + // bookkeeping, but for non-compressible data (such as JPEG) it's a huge + // win since the compressor quickly "realizes" the data is incompressible + // and doesn't bother looking for matches everywhere. + // + // The "skip" variable keeps track of how many bytes there are since the + // last match; dividing it by 32 (ie. right-shifting by five) gives the + // number of bytes to move ahead for each iteration. + uint32_t skip = 32; + + const uint8_t* next_ip = ip; + const uint8_t* candidate; + do { + ip = next_ip; + uint32_t hash = next_hash; + assert(hash == Hash(ip, shift)); + uint32_t bytes_between_hash_lookups = skip++ >> 5; + next_ip = ip + bytes_between_hash_lookups; + if (PREDICT_FALSE(next_ip > ip_limit)) { + goto emit_remainder; + } + next_hash = Hash(next_ip, shift); + candidate = ip - last_distance; + if (IsMatch(ip, candidate)) { + if (PREDICT_TRUE(candidate < ip)) { + table[hash] = static_cast<int>(ip - base_ip); + break; + } + } + candidate = base_ip + table[hash]; + assert(candidate >= base_ip); + assert(candidate < ip); + + table[hash] = static_cast<int>(ip - base_ip); + } while (PREDICT_TRUE(!IsMatch(ip, candidate))); + + // Step 2: Emit the found match together with the literal bytes from + // "next_emit" to the bit stream, and then see if we can find a next macth + // immediately afterwards. Repeat until we find no match for the input + // without emitting some literal bytes. + uint64_t input_bytes; + + { + // We have a 5-byte match at ip, and we need to emit bytes in + // [next_emit, ip). + const uint8_t* base = ip; + size_t matched = 5 + FindMatchLengthWithLimit( + candidate + 5, ip + 5, static_cast<size_t>(ip_end - ip) - 5); + ip += matched; + int distance = static_cast<int>(base - candidate); /* > 0 */ + size_t insert = static_cast<size_t>(base - next_emit); + assert(0 == memcmp(base, candidate, matched)); + if (PREDICT_TRUE(insert < 6210)) { + EmitInsertLen(insert, cmd_depth, cmd_bits, cmd_histo, + storage_ix, storage); + } else if (ShouldUseUncompressedMode(metablock_start, next_emit, insert, + lit_depth)) { + EmitUncompressedMetaBlock(metablock_start, base, mlen_storage_ix - 3, + storage_ix, storage); + input_size -= static_cast<size_t>(base - input); + input = base; + next_emit = input; + goto next_block; + } else { + EmitLongInsertLen(insert, cmd_depth, cmd_bits, cmd_histo, + storage_ix, storage); + } + EmitLiterals(next_emit, insert, lit_depth, lit_bits, + storage_ix, storage); + if (distance == last_distance) { + WriteBits(cmd_depth[64], cmd_bits[64], storage_ix, storage); + ++cmd_histo[64]; + } else { + EmitDistance(static_cast<size_t>(distance), cmd_depth, cmd_bits, + cmd_histo, storage_ix, storage); + last_distance = distance; + } + EmitCopyLenLastDistance(matched, cmd_depth, cmd_bits, cmd_histo, + storage_ix, storage); + + next_emit = ip; + if (PREDICT_FALSE(ip >= ip_limit)) { + goto emit_remainder; + } + // We could immediately start working at ip now, but to improve + // compression we first update "table" with the hashes of some positions + // within the last copy. + input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 3); + uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift); + table[prev_hash] = static_cast<int>(ip - base_ip - 3); + prev_hash = HashBytesAtOffset(input_bytes, 1, shift); + table[prev_hash] = static_cast<int>(ip - base_ip - 2); + prev_hash = HashBytesAtOffset(input_bytes, 2, shift); + table[prev_hash] = static_cast<int>(ip - base_ip - 1); + + uint32_t cur_hash = HashBytesAtOffset(input_bytes, 3, shift); + candidate = base_ip + table[cur_hash]; + table[cur_hash] = static_cast<int>(ip - base_ip); + } + + while (IsMatch(ip, candidate)) { + // We have a 5-byte match at ip, and no need to emit any literal bytes + // prior to ip. + const uint8_t* base = ip; + size_t matched = 5 + FindMatchLengthWithLimit( + candidate + 5, ip + 5, static_cast<size_t>(ip_end - ip) - 5); + ip += matched; + last_distance = static_cast<int>(base - candidate); /* > 0 */ + assert(0 == memcmp(base, candidate, matched)); + EmitCopyLen(matched, cmd_depth, cmd_bits, cmd_histo, + storage_ix, storage); + EmitDistance(static_cast<size_t>(last_distance), cmd_depth, cmd_bits, + cmd_histo, storage_ix, storage); + + next_emit = ip; + if (PREDICT_FALSE(ip >= ip_limit)) { + goto emit_remainder; + } + // We could immediately start working at ip now, but to improve + // compression we first update "table" with the hashes of some positions + // within the last copy. + input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 3); + uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift); + table[prev_hash] = static_cast<int>(ip - base_ip - 3); + prev_hash = HashBytesAtOffset(input_bytes, 1, shift); + table[prev_hash] = static_cast<int>(ip - base_ip - 2); + prev_hash = HashBytesAtOffset(input_bytes, 2, shift); + table[prev_hash] = static_cast<int>(ip - base_ip - 1); + + uint32_t cur_hash = HashBytesAtOffset(input_bytes, 3, shift); + candidate = base_ip + table[cur_hash]; + table[cur_hash] = static_cast<int>(ip - base_ip); + } + + next_hash = Hash(++ip, shift); + } + } + + emit_remainder: + assert(next_emit <= ip_end); + input += block_size; + input_size -= block_size; + block_size = std::min(input_size, kMergeBlockSize); + + // Decide if we want to continue this meta-block instead of emitting the + // last insert-only command. + if (input_size > 0 && + total_block_size + block_size <= (1 << 20) && + ShouldMergeBlock(input, block_size, lit_depth)) { + assert(total_block_size > (1 << 16)); + // Update the size of the current meta-block and continue emitting commands. + // We can do this because the current size and the new size both have 5 + // nibbles. + total_block_size += block_size; + UpdateBits(20, static_cast<uint32_t>(total_block_size - 1), + mlen_storage_ix, storage); + goto emit_commands; + } + + // Emit the remaining bytes as literals. + if (next_emit < ip_end) { + const size_t insert = static_cast<size_t>(ip_end - next_emit); + if (PREDICT_TRUE(insert < 6210)) { + EmitInsertLen(insert, cmd_depth, cmd_bits, cmd_histo, + storage_ix, storage); + EmitLiterals(next_emit, insert, lit_depth, lit_bits, storage_ix, storage); + } else if (ShouldUseUncompressedMode(metablock_start, next_emit, insert, + lit_depth)) { + EmitUncompressedMetaBlock(metablock_start, ip_end, mlen_storage_ix - 3, + storage_ix, storage); + } else { + EmitLongInsertLen(insert, cmd_depth, cmd_bits, cmd_histo, + storage_ix, storage); + EmitLiterals(next_emit, insert, lit_depth, lit_bits, + storage_ix, storage); + } + } + next_emit = ip_end; + +next_block: + // If we have more data, write a new meta-block header and prefix codes and + // then continue emitting commands. + if (input_size > 0) { + metablock_start = input; + block_size = std::min(input_size, kFirstBlockSize); + total_block_size = block_size; + // Save the bit position of the MLEN field of the meta-block header, so that + // we can update it later if we decide to extend this meta-block. + mlen_storage_ix = *storage_ix + 3; + StoreMetaBlockHeader(block_size, 0, storage_ix, storage); + // No block splits, no contexts. + WriteBits(13, 0, storage_ix, storage); + memset(lit_depth, 0, sizeof(lit_depth)); + memset(lit_bits, 0, sizeof(lit_bits)); + BuildAndStoreLiteralPrefixCode(input, block_size, lit_depth, lit_bits, + storage_ix, storage); + BuildAndStoreCommandPrefixCode(cmd_histo, cmd_depth, cmd_bits, + storage_ix, storage); + goto emit_commands; + } + + if (is_last) { + WriteBits(1, 1, storage_ix, storage); // islast + WriteBits(1, 1, storage_ix, storage); // isempty + *storage_ix = (*storage_ix + 7u) & ~7u; + } else { + // If this is not the last block, update the command and distance prefix + // codes for the next block and store the compressed forms. + cmd_code[0] = 0; + *cmd_code_numbits = 0; + BuildAndStoreCommandPrefixCode(cmd_histo, cmd_depth, cmd_bits, + cmd_code_numbits, cmd_code); + } +} + +} // namespace brotli |