Added brotli enc/ and tools/ directories.

third_party/brotli/enc/compress_fragment_two_pass.cc

+/* 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 "./types.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) {
+  // Tree size for building a tree over 64 symbols is 2 * 64 + 1.
+  static const size_t kTreeSize = 129;
+  HuffmanTree tree[kTreeSize];
+  CreateHuffmanTree(histogram, 64, 15, tree, depth);
+  CreateHuffmanTree(&histogram[64], 64, 14, tree, &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, tree, storage_ix, storage);
+  }
+  StoreHuffmanTree(&depth[64], 64, tree, 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);
+}
+
+static 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(table_size - 1 == static_cast<size_t>(
+      MAKE_UINT64_T(0xFFFFFFFF, 0xFFFFFF) >> shift));
+  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;
+  }
+}
+
+static 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;
+      }
+    }
+  }
+}
+
+static 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