diff options
Diffstat (limited to 'debian/vendor-h2o/deps/brotli/enc/compress_fragment_two_pass.cc')
| -rw-r--r-- | debian/vendor-h2o/deps/brotli/enc/compress_fragment_two_pass.cc | 519 |
1 files changed, 0 insertions, 519 deletions
diff --git a/debian/vendor-h2o/deps/brotli/enc/compress_fragment_two_pass.cc b/debian/vendor-h2o/deps/brotli/enc/compress_fragment_two_pass.cc deleted file mode 100644 index 8477603..0000000 --- a/debian/vendor-h2o/deps/brotli/enc/compress_fragment_two_pass.cc +++ /dev/null @@ -1,519 +0,0 @@ -/* 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 two-pass processing: in the first pass we save -// the found backward matches and literal bytes into a buffer, and in the -// second pass we emit them into the bit stream using prefix codes built based -// on the actual command and literal byte histograms. - -#include "./compress_fragment_two_pass.h" - -#include <algorithm> - -#include "./brotli_bit_stream.h" -#include "./bit_cost.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) << 16) * 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 <= 2); - const uint64_t h = ((v >> (8 * offset)) << 16) * 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] && - p1[5] == p2[5]); -} - -// Builds a command and distance prefix code (each 64 symbols) into "depth" and -// "bits" based on "histogram" and stores it into the bit stream. -static 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, 24); - memcpy(cmd_depth + 24, depth, 8); - memcpy(cmd_depth + 32, depth + 48, 8); - memcpy(cmd_depth + 40, depth + 8, 8); - memcpy(cmd_depth + 48, depth + 56, 8); - memcpy(cmd_depth + 56, depth + 16, 8); - ConvertBitDepthsToSymbols(cmd_depth, 64, cmd_bits); - memcpy(bits, cmd_bits + 24, 16); - memcpy(bits + 8, cmd_bits + 40, 16); - memcpy(bits + 16, cmd_bits + 56, 16); - memcpy(bits + 24, cmd_bits, 48); - memcpy(bits + 48, cmd_bits + 32, 16); - memcpy(bits + 56, cmd_bits + 48, 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 + 24, 8); - memcpy(cmd_depth + 64, depth + 32, 8); - memcpy(cmd_depth + 128, depth + 40, 8); - memcpy(cmd_depth + 192, depth + 48, 8); - memcpy(cmd_depth + 384, depth + 56, 8); - for (size_t i = 0; i < 8; ++i) { - cmd_depth[128 + 8 * i] = depth[i]; - cmd_depth[256 + 8 * i] = depth[8 + i]; - cmd_depth[448 + 8 * i] = depth[16 + i]; - } - StoreHuffmanTree(cmd_depth, 704, storage_ix, storage); - } - StoreHuffmanTree(&depth[64], 64, storage_ix, storage); -} - -inline void EmitInsertLen(uint32_t insertlen, uint32_t** commands) { - if (insertlen < 6) { - **commands = insertlen; - } else if (insertlen < 130) { - insertlen -= 2; - const uint32_t nbits = Log2FloorNonZero(insertlen) - 1u; - const uint32_t prefix = insertlen >> nbits; - const uint32_t inscode = (nbits << 1) + prefix + 2; - const uint32_t extra = insertlen - (prefix << nbits); - **commands = inscode | (extra << 8); - } else if (insertlen < 2114) { - insertlen -= 66; - const uint32_t nbits = Log2FloorNonZero(insertlen); - const uint32_t code = nbits + 10; - const uint32_t extra = insertlen - (1 << nbits); - **commands = code | (extra << 8); - } else if (insertlen < 6210) { - const uint32_t extra = insertlen - 2114; - **commands = 21 | (extra << 8); - } else if (insertlen < 22594) { - const uint32_t extra = insertlen - 6210; - **commands = 22 | (extra << 8); - } else { - const uint32_t extra = insertlen - 22594; - **commands = 23 | (extra << 8); - } - ++(*commands); -} - -inline void EmitCopyLen(size_t copylen, uint32_t** commands) { - if (copylen < 10) { - **commands = static_cast<uint32_t>(copylen + 38); - } else if (copylen < 134) { - copylen -= 6; - const size_t nbits = Log2FloorNonZero(copylen) - 1; - const size_t prefix = copylen >> nbits; - const size_t code = (nbits << 1) + prefix + 44; - const size_t extra = copylen - (prefix << nbits); - **commands = static_cast<uint32_t>(code | (extra << 8)); - } else if (copylen < 2118) { - copylen -= 70; - const size_t nbits = Log2FloorNonZero(copylen); - const size_t code = nbits + 52; - const size_t extra = copylen - (1 << nbits); - **commands = static_cast<uint32_t>(code | (extra << 8)); - } else { - const size_t extra = copylen - 2118; - **commands = static_cast<uint32_t>(63 | (extra << 8)); - } - ++(*commands); -} - -inline void EmitCopyLenLastDistance(size_t copylen, uint32_t** commands) { - if (copylen < 12) { - **commands = static_cast<uint32_t>(copylen + 20); - ++(*commands); - } else if (copylen < 72) { - copylen -= 8; - const size_t nbits = Log2FloorNonZero(copylen) - 1; - const size_t prefix = copylen >> nbits; - const size_t code = (nbits << 1) + prefix + 28; - const size_t extra = copylen - (prefix << nbits); - **commands = static_cast<uint32_t>(code | (extra << 8)); - ++(*commands); - } else if (copylen < 136) { - copylen -= 8; - const size_t code = (copylen >> 5) + 54; - const size_t extra = copylen & 31; - **commands = static_cast<uint32_t>(code | (extra << 8)); - ++(*commands); - **commands = 64; - ++(*commands); - } else if (copylen < 2120) { - copylen -= 72; - const size_t nbits = Log2FloorNonZero(copylen); - const size_t code = nbits + 52; - const size_t extra = copylen - (1 << nbits); - **commands = static_cast<uint32_t>(code | (extra << 8)); - ++(*commands); - **commands = 64; - ++(*commands); - } else { - const size_t extra = copylen - 2120; - **commands = static_cast<uint32_t>(63 | (extra << 8)); - ++(*commands); - **commands = 64; - ++(*commands); - } -} - -inline void EmitDistance(uint32_t distance, uint32_t** commands) { - distance += 3; - uint32_t nbits = Log2FloorNonZero(distance) - 1; - const uint32_t prefix = (distance >> nbits) & 1; - const uint32_t offset = (2 + prefix) << nbits; - const uint32_t distcode = 2 * (nbits - 1) + prefix + 80; - uint32_t extra = distance - offset; - **commands = distcode | (extra << 8); - ++(*commands); -} - -// 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 CreateCommands(const uint8_t* input, size_t block_size, size_t input_size, - const uint8_t* base_ip, - int* table, size_t table_size, - uint8_t** literals, uint32_t** commands) { - // "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; - // "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; - - int last_distance = -1; - const size_t kInputMarginBytes = 16; - const size_t kMinMatchLen = 6; - 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 6-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", 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 6-byte match at ip, and we need to emit bytes in - // [next_emit, ip). - const uint8_t* base = ip; - size_t matched = 6 + FindMatchLengthWithLimit( - candidate + 6, ip + 6, static_cast<size_t>(ip_end - ip) - 6); - ip += matched; - int distance = static_cast<int>(base - candidate); /* > 0 */ - int insert = static_cast<int>(base - next_emit); - assert(0 == memcmp(base, candidate, matched)); - EmitInsertLen(static_cast<uint32_t>(insert), commands); - memcpy(*literals, next_emit, static_cast<size_t>(insert)); - *literals += insert; - if (distance == last_distance) { - **commands = 64; - ++(*commands); - } else { - EmitDistance(static_cast<uint32_t>(distance), commands); - last_distance = distance; - } - EmitCopyLenLastDistance(matched, commands); - - 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 - 5); - uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 5); - prev_hash = HashBytesAtOffset(input_bytes, 1, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 4); - prev_hash = HashBytesAtOffset(input_bytes, 2, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 3); - input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 2); - prev_hash = HashBytesAtOffset(input_bytes, 0, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 2); - prev_hash = HashBytesAtOffset(input_bytes, 1, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 1); - - uint32_t cur_hash = HashBytesAtOffset(input_bytes, 2, shift); - candidate = base_ip + table[cur_hash]; - table[cur_hash] = static_cast<int>(ip - base_ip); - } - - while (IsMatch(ip, candidate)) { - // We have a 6-byte match at ip, and no need to emit any - // literal bytes prior to ip. - const uint8_t* base = ip; - size_t matched = 6 + FindMatchLengthWithLimit( - candidate + 6, ip + 6, static_cast<size_t>(ip_end - ip) - 6); - ip += matched; - last_distance = static_cast<int>(base - candidate); /* > 0 */ - assert(0 == memcmp(base, candidate, matched)); - EmitCopyLen(matched, commands); - EmitDistance(static_cast<uint32_t>(last_distance), commands); - - 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 - 5); - uint32_t prev_hash = HashBytesAtOffset(input_bytes, 0, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 5); - prev_hash = HashBytesAtOffset(input_bytes, 1, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 4); - prev_hash = HashBytesAtOffset(input_bytes, 2, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 3); - input_bytes = BROTLI_UNALIGNED_LOAD64(ip - 2); - prev_hash = HashBytesAtOffset(input_bytes, 0, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 2); - prev_hash = HashBytesAtOffset(input_bytes, 1, shift); - table[prev_hash] = static_cast<int>(ip - base_ip - 1); - - uint32_t cur_hash = HashBytesAtOffset(input_bytes, 2, 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); - // Emit the remaining bytes as literals. - if (next_emit < ip_end) { - const uint32_t insert = static_cast<uint32_t>(ip_end - next_emit); - EmitInsertLen(insert, commands); - memcpy(*literals, next_emit, insert); - *literals += insert; - } -} - -void StoreCommands(const uint8_t* literals, const size_t num_literals, - const uint32_t* commands, const size_t num_commands, - size_t* storage_ix, uint8_t* storage) { - uint8_t lit_depths[256] = { 0 }; - uint16_t lit_bits[256] = { 0 }; - uint32_t lit_histo[256] = { 0 }; - for (size_t i = 0; i < num_literals; ++i) { - ++lit_histo[literals[i]]; - } - BuildAndStoreHuffmanTreeFast(lit_histo, num_literals, - /* max_bits = */ 8, - lit_depths, lit_bits, - storage_ix, storage); - - uint8_t cmd_depths[128] = { 0 }; - uint16_t cmd_bits[128] = { 0 }; - uint32_t cmd_histo[128] = { 0 }; - for (size_t i = 0; i < num_commands; ++i) { - ++cmd_histo[commands[i] & 0xff]; - } - cmd_histo[1] += 1; - cmd_histo[2] += 1; - cmd_histo[64] += 1; - cmd_histo[84] += 1; - BuildAndStoreCommandPrefixCode(cmd_histo, cmd_depths, cmd_bits, - storage_ix, storage); - - static const uint32_t kNumExtraBits[128] = { - 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 7, 8, 9, 10, 12, 14, 24, - 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, - 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 7, 8, 9, 10, 24, - 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, - 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, - 9, 9, 10, 10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16, - 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 23, 24, 24, - }; - static const uint32_t kInsertOffset[24] = { - 0, 1, 2, 3, 4, 5, 6, 8, 10, 14, 18, 26, 34, 50, 66, 98, 130, 194, 322, 578, - 1090, 2114, 6210, 22594, - }; - - for (size_t i = 0; i < num_commands; ++i) { - const uint32_t cmd = commands[i]; - const uint32_t code = cmd & 0xff; - const uint32_t extra = cmd >> 8; - WriteBits(cmd_depths[code], cmd_bits[code], storage_ix, storage); - WriteBits(kNumExtraBits[code], extra, storage_ix, storage); - if (code < 24) { - const uint32_t insert = kInsertOffset[code] + extra; - for (uint32_t j = 0; j < insert; ++j) { - const uint8_t lit = *literals; - WriteBits(lit_depths[lit], lit_bits[lit], storage_ix, storage); - ++literals; - } - } - } -} - -bool ShouldCompress(const uint8_t* input, size_t input_size, - size_t num_literals) { - static const double kAcceptableLossForUncompressibleSpeedup = 0.02; - static const double kMaxRatioOfLiterals = - 1.0 - kAcceptableLossForUncompressibleSpeedup; - if (num_literals < kMaxRatioOfLiterals * static_cast<double>(input_size)) { - return true; - } - uint32_t literal_histo[256] = { 0 }; - static const uint32_t kSampleRate = 43; - static const double kMaxEntropy = - 8 * (1.0 - kAcceptableLossForUncompressibleSpeedup); - const double max_total_bit_cost = - static_cast<double>(input_size) * kMaxEntropy / kSampleRate; - for (size_t i = 0; i < input_size; i += kSampleRate) { - ++literal_histo[input[i]]; - } - return BitsEntropy(literal_histo, 256) < max_total_bit_cost; -} - -void BrotliCompressFragmentTwoPass(const uint8_t* input, size_t input_size, - bool is_last, - uint32_t* command_buf, uint8_t* literal_buf, - int* table, size_t table_size, - size_t* storage_ix, uint8_t* storage) { - // Save the start of the first block for position and distance computations. - const uint8_t* base_ip = input; - - while (input_size > 0) { - size_t block_size = std::min(input_size, kCompressFragmentTwoPassBlockSize); - uint32_t* commands = command_buf; - uint8_t* literals = literal_buf; - CreateCommands(input, block_size, input_size, base_ip, table, table_size, - &literals, &commands); - const size_t num_literals = static_cast<size_t>(literals - literal_buf); - const size_t num_commands = static_cast<size_t>(commands - command_buf); - if (ShouldCompress(input, block_size, num_literals)) { - StoreMetaBlockHeader(block_size, 0, storage_ix, storage); - // No block splits, no contexts. - WriteBits(13, 0, storage_ix, storage); - StoreCommands(literal_buf, num_literals, command_buf, num_commands, - storage_ix, storage); - } else { - // Since we did not find many backward references and the entropy of - // the data is close to 8 bits, we can simply emit an uncompressed block. - // This makes compression speed of uncompressible data about 3x faster. - StoreMetaBlockHeader(block_size, 1, storage_ix, storage); - *storage_ix = (*storage_ix + 7u) & ~7u; - memcpy(&storage[*storage_ix >> 3], input, block_size); - *storage_ix += block_size << 3; - storage[*storage_ix >> 3] = 0; - } - input += block_size; - input_size -= block_size; - } - - if (is_last) { - WriteBits(1, 1, storage_ix, storage); // islast - WriteBits(1, 1, storage_ix, storage); // isempty - *storage_ix = (*storage_ix + 7u) & ~7u; - } -} - -} // namespace brotli |