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Merge pull request #306 from szabadka/master

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Use a hash-to-binary-tree data structure for quality 11 as suggested by Issue #180
This commit is contained in:
szabadka 2016-01-27 10:19:19 +01:00
commit 058d7498a1
6 changed files with 319 additions and 68 deletions
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80
enc/backward_references.cc
View File

@ -18,6 +18,9 @@
namespace brotli {
// The maximum length for which the zopflification uses distinct distances.
static const uint16_t kMaxZopfliLen = 325;
static const double kInfinity = std::numeric_limits<double>::infinity();
// Histogram based cost model for zopflification.
@ -483,14 +486,17 @@ void CreateBackwardReferences(size_t num_bytes,
bool is_last,
const uint8_t* ringbuffer,
size_t ringbuffer_mask,
const size_t max_backward_limit,
const int quality,
const int lgwin,
Hasher* hasher,
int* dist_cache,
size_t* last_insert_len,
Command* commands,
size_t* num_commands,
size_t* num_literals) {
// Set maximum distance, see section 9.1. of the spec.
const size_t max_backward_limit = (1 << lgwin) - 16;
// Choose which init method is faster.
// memset is about 100 times faster than hasher->InitForData().
const size_t kMaxBytesForPartialHashInit = Hasher::kHashMapSize >> 7;
@ -545,7 +551,6 @@ void CreateBackwardReferences(size_t num_bytes,
size_t best_dist_2 = 0;
double best_score_2 = kMinScore;
max_distance = std::min(i + i_diff + 1, max_backward_limit);
hasher->Store(ringbuffer + i, static_cast<uint32_t>(i + i_diff));
match_found = hasher->FindLongestMatch(
ringbuffer, ringbuffer_mask,
dist_cache, static_cast<uint32_t>(i + i_diff + 1),
@ -585,14 +590,13 @@ void CreateBackwardReferences(size_t num_bytes,
insert_length = 0;
// Put the hash keys into the table, if there are enough
// bytes left.
for (size_t j = 1; j < best_len; ++j) {
for (size_t j = 2; j < best_len; ++j) {
hasher->Store(&ringbuffer[i + j],
static_cast<uint32_t>(i + i_diff + j));
}
i += best_len;
} else {
++insert_length;
hasher->Store(ringbuffer + i, static_cast<uint32_t>(i + i_diff));
++i;
// If we have not seen matches for a long time, we can skip some
// match lookups. Unsuccessful match lookups are very very expensive
@ -632,8 +636,8 @@ void CreateBackwardReferences(size_t num_bytes,
bool is_last,
const uint8_t* ringbuffer,
size_t ringbuffer_mask,
const size_t max_backward_limit,
const int quality,
const int lgwin,
Hashers* hashers,
int hash_type,
int* dist_cache,
@ -643,45 +647,53 @@ void CreateBackwardReferences(size_t num_bytes,
size_t* num_literals) {
bool zopflify = quality > 9;
if (zopflify) {
Hashers::H9* hasher = hashers->hash_h9;
hasher->Init();
if (num_bytes >= 3 && position >= 3) {
// Prepare the hashes for three last bytes of the last write.
Hashers::H10* hasher = hashers->hash_h10;
hasher->Init(lgwin, position, num_bytes, is_last);
if (num_bytes >= 3 && position >= kMaxTreeCompLength) {
// Store the last `kMaxTreeCompLength - 1` positions in the hasher.
// These could not be calculated before, since they require knowledge
// of both the previous and the current block.
hasher->Store(&ringbuffer[(position - 3) & ringbuffer_mask],
static_cast<uint32_t>(position - 3));
hasher->Store(&ringbuffer[(position - 2) & ringbuffer_mask],
static_cast<uint32_t>(position - 2));
hasher->Store(&ringbuffer[(position - 1) & ringbuffer_mask],
static_cast<uint32_t>(position - 1));
for (size_t i = position - kMaxTreeCompLength + 1; i < position; ++i) {
hasher->Store(ringbuffer, ringbuffer_mask, i, num_bytes + position - i);
}
}
// Set maximum distance, see section 9.1. of the spec.
const size_t max_backward_limit = (1 << lgwin) - 16;
std::vector<uint32_t> num_matches(num_bytes);
std::vector<BackwardMatch> matches(3 * num_bytes);
std::vector<BackwardMatch> matches(4 * num_bytes);
size_t cur_match_pos = 0;
for (size_t i = 0; i + 3 < num_bytes; ++i) {
size_t max_distance = std::min(position + i, max_backward_limit);
size_t max_length = num_bytes - i;
// Ensure that we have at least kMaxZopfliLen free slots.
if (matches.size() < cur_match_pos + kMaxZopfliLen) {
matches.resize(cur_match_pos + kMaxZopfliLen);
// Ensure that we have enough free slots.
if (matches.size() < cur_match_pos + Hashers::H10::kMaxNumMatches) {
matches.resize(cur_match_pos + Hashers::H10::kMaxNumMatches);
}
size_t num_found_matches = hasher->FindAllMatches(
ringbuffer, ringbuffer_mask, position + i, max_length, max_distance,
&matches[cur_match_pos]);
const size_t cur_match_end = cur_match_pos + num_found_matches;
for (size_t j = cur_match_pos; j + 1 < cur_match_end; ++j) {
assert(matches[j].length() < matches[j + 1].length());
assert(matches[j].distance > max_distance ||
matches[j].distance <= matches[j + 1].distance);
}
num_matches[i] = static_cast<uint32_t>(num_found_matches);
hasher->Store(&ringbuffer[(position + i) & ringbuffer_mask],
static_cast<uint32_t>(position + i));
cur_match_pos += num_found_matches;
if (num_found_matches == 1) {
const size_t match_len = matches[cur_match_pos - 1].length();
if (num_found_matches > 0) {
const size_t match_len = matches[cur_match_end - 1].length();
if (match_len > kMaxZopfliLen) {
matches[cur_match_pos++] = matches[cur_match_end - 1];
num_matches[i] = 1;
for (size_t j = 1; j < match_len; ++j) {
++i;
hasher->Store(&ringbuffer[(position + i) & ringbuffer_mask],
static_cast<uint32_t>(position + i));
if (match_len - j < 64) {
hasher->Store(ringbuffer, ringbuffer_mask, position + i,
num_bytes - i);
}
num_matches[i] = 0;
}
} else {
cur_match_pos = cur_match_end;
}
}
}
@ -718,49 +730,49 @@ void CreateBackwardReferences(size_t num_bytes,
case 2:
CreateBackwardReferences<Hashers::H2>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h2, dist_cache,
quality, lgwin, hashers->hash_h2, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 3:
CreateBackwardReferences<Hashers::H3>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h3, dist_cache,
quality, lgwin, hashers->hash_h3, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 4:
CreateBackwardReferences<Hashers::H4>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h4, dist_cache,
quality, lgwin, hashers->hash_h4, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 5:
CreateBackwardReferences<Hashers::H5>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h5, dist_cache,
quality, lgwin, hashers->hash_h5, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 6:
CreateBackwardReferences<Hashers::H6>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h6, dist_cache,
quality, lgwin, hashers->hash_h6, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 7:
CreateBackwardReferences<Hashers::H7>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h7, dist_cache,
quality, lgwin, hashers->hash_h7, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 8:
CreateBackwardReferences<Hashers::H8>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h8, dist_cache,
quality, lgwin, hashers->hash_h8, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
case 9:
CreateBackwardReferences<Hashers::H9>(
num_bytes, position, is_last, ringbuffer, ringbuffer_mask,
max_backward_limit, quality, hashers->hash_h9, dist_cache,
quality, lgwin, hashers->hash_h9, dist_cache,
last_insert_len, commands, num_commands, num_literals);
break;
default:

2
enc/backward_references.h
View File

@ -24,8 +24,8 @@ void CreateBackwardReferences(size_t num_bytes,
bool is_last,
const uint8_t* ringbuffer,
size_t ringbuffer_mask,
const size_t max_backward_limit,
const int quality,
const int lgwin,
Hashers* hashers,
int hash_type,
int* dist_cache,

9
enc/encode.cc
View File

@ -217,9 +217,6 @@ BrotliCompressor::BrotliCompressor(BrotliParams params)
std::max(kMinInputBlockBits, params_.lgblock));
}
// Set maximum distance, see section 9.1. of the spec.
max_backward_distance_ = (1 << params_.lgwin) - 16;
// Initialize input and literal cost ring buffers.
// We allocate at least lgwin + 1 bits for the ring buffer so that the newly
// added block fits there completely and we still get lgwin bits and at least
@ -252,7 +249,7 @@ BrotliCompressor::BrotliCompressor(BrotliParams params)
}
// Initialize hashers.
hash_type_ = std::min(9, params_.quality);
hash_type_ = std::min(10, params_.quality);
hashers_->Init(hash_type_);
}
@ -328,7 +325,7 @@ void BrotliCompressor::BrotliSetCustomDictionary(
if (size > 1) {
prev_byte2_ = dict[size - 2];
}
hashers_->PrependCustomDictionary(hash_type_, size, dict);
hashers_->PrependCustomDictionary(hash_type_, params_.lgwin, size, dict);
}
bool BrotliCompressor::WriteBrotliData(const bool is_last,
@ -394,8 +391,8 @@ bool BrotliCompressor::WriteBrotliData(const bool is_last,
CreateBackwardReferences(bytes, WrapPosition(last_processed_pos_),
is_last, data, mask,
max_backward_distance_,
params_.quality,
params_.lgwin,
hashers_,
hash_type_,
dist_cache_,

1
enc/encode.h
View File

@ -145,7 +145,6 @@ class BrotliCompressor {
uint8_t** output);
BrotliParams params_;
size_t max_backward_distance_;
Hashers* hashers_;
int hash_type_;
uint64_t input_pos_;

5
enc/encode_parallel.cc
View File

@ -85,7 +85,7 @@ bool WriteMetaBlockParallel(const BrotliParams& params,
kMinUTF8Ratio);
// Initialize hashers.
int hash_type = std::min(9, params.quality);
int hash_type = std::min(10, params.quality);
Hashers* hashers = new Hashers();
hashers->Init(hash_type);
@ -93,7 +93,6 @@ bool WriteMetaBlockParallel(const BrotliParams& params,
size_t last_insert_len = 0;
size_t num_commands = 0;
size_t num_literals = 0;
uint32_t max_backward_distance = (1 << params.lgwin) - 16;
int dist_cache[4] = { -4, -4, -4, -4 };
Command* commands = static_cast<Command*>(
malloc(sizeof(Command) * ((input_size + 1) >> 1)));
@ -104,8 +103,8 @@ bool WriteMetaBlockParallel(const BrotliParams& params,
CreateBackwardReferences(
input_size, input_pos, is_last,
&input[0], mask,
max_backward_distance,
params.quality,
params.lgwin,
hashers,
hash_type,
dist_cache,

290
enc/hash.h
View File

@ -13,6 +13,7 @@
#include <sys/types.h>
#include <algorithm>
#include <cstring>
#include <limits>
#include <vector>
#include "./dictionary_hash.h"
@ -26,6 +27,9 @@
namespace brotli {
static const size_t kMaxTreeSearchDepth = 64;
static const size_t kMaxTreeCompLength = 128;
static const uint32_t kDistanceCacheIndex[] = {
0, 1, 2, 3, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1,
};
@ -155,7 +159,8 @@ class HashLongestMatchQuickly {
}
// Find a longest backward match of &ring_buffer[cur_ix & ring_buffer_mask]
// up to the length of max_length.
// up to the length of max_length and stores the position cur_ix in the
// hash table.
//
// Does not look for matches longer than max_length.
// Does not look for matches further away than max_backward.
@ -174,6 +179,7 @@ class HashLongestMatchQuickly {
double* __restrict best_score_out) {
const size_t best_len_in = *best_len_out;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
const uint32_t key = HashBytes(&ring_buffer[cur_ix_masked]);
int compare_char = ring_buffer[cur_ix_masked + best_len_in];
double best_score = *best_score_out;
size_t best_len = best_len_in;
@ -195,6 +201,7 @@ class HashLongestMatchQuickly {
*best_score_out = best_score;
compare_char = ring_buffer[cur_ix_masked + best_len];
if (kBucketSweep == 1) {
buckets_[key] = static_cast<uint32_t>(cur_ix);
return true;
} else {
match_found = true;
@ -202,10 +209,10 @@ class HashLongestMatchQuickly {
}
}
}
const uint32_t key = HashBytes(&ring_buffer[cur_ix_masked]);
if (kBucketSweep == 1) {
// Only one to look for, don't bother to prepare for a loop.
prev_ix = buckets_[key];
buckets_[key] = static_cast<uint32_t>(cur_ix);
size_t backward = cur_ix - prev_ix;
prev_ix &= static_cast<uint32_t>(ring_buffer_mask);
if (compare_char != ring_buffer[prev_ix + best_len_in]) {
@ -283,12 +290,14 @@ class HashLongestMatchQuickly {
*best_len_code_out = len;
*best_distance_out = backward;
*best_score_out = best_score;
return true;
match_found = true;
}
}
}
}
}
const uint32_t off = (cur_ix >> 3) % kBucketSweep;
buckets_[key + off] = static_cast<uint32_t>(cur_ix);
return match_found;
}
@ -317,9 +326,6 @@ class HashLongestMatchQuickly {
size_t num_dict_matches_;
};
// The maximum length for which the zopflification uses distinct distances.
static const uint16_t kMaxZopfliLen = 325;
// A (forgetful) hash table to the data seen by the compressor, to
// help create backward references to previous data.
//
@ -366,7 +372,7 @@ class HashLongestMatch {
}
// Find a longest backward match of &data[cur_ix] up to the length of
// max_length.
// max_length and stores the position cur_ix in the hash table.
//
// Does not look for matches longer than max_length.
// Does not look for matches further away than max_backward.
@ -464,6 +470,8 @@ class HashLongestMatch {
}
}
}
buckets_[key][num_[key] & kBlockMask] = static_cast<uint32_t>(cur_ix);
++num_[key];
if (!match_found && num_dict_matches_ >= (num_dict_lookups_ >> 7)) {
size_t dict_key = Hash<14>(&data[cur_ix_masked]) << 1;
for (int k = 0; k < 2; ++k, ++dict_key) {
@ -503,21 +511,19 @@ class HashLongestMatch {
return match_found;
}
// Similar to FindLongestMatch(), but finds all matches.
// Finds all backward matches of &data[cur_ix & ring_buffer_mask] up to the
// length of max_length and stores the position cur_ix in the hash table.
//
// Sets *num_matches to the number of matches found, and stores the found
// matches in matches[0] to matches[*num_matches - 1].
//
// If the longest match is longer than kMaxZopfliLen, returns only this
// longest match.
//
// Requires that at least kMaxZopfliLen space is available in matches.
// matches in matches[0] to matches[*num_matches - 1]. The matches will be
// sorted by strictly increasing length and (non-strictly) increasing
// distance.
size_t FindAllMatches(const uint8_t* data,
const size_t ring_buffer_mask,
const size_t cur_ix,
const size_t max_length,
const size_t max_backward,
BackwardMatch* matches) const {
BackwardMatch* matches) {
BackwardMatch* const orig_matches = matches;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
size_t best_len = 1;
@ -539,9 +545,6 @@ class HashLongestMatch {
max_length);
if (len > best_len) {
best_len = len;
if (len > kMaxZopfliLen) {
matches = orig_matches;
}
*matches++ = BackwardMatch(backward, len);
}
}
@ -566,12 +569,11 @@ class HashLongestMatch {
max_length);
if (len > best_len) {
best_len = len;
if (len > kMaxZopfliLen) {
matches = orig_matches;
}
*matches++ = BackwardMatch(backward, len);
}
}
buckets_[key][num_[key] & kBlockMask] = static_cast<uint32_t>(cur_ix);
++num_[key];
std::vector<uint32_t> dict_matches(kMaxDictionaryMatchLen + 1,
kInvalidMatch);
size_t minlen = std::max<size_t>(4, best_len + 1);
@ -604,6 +606,8 @@ class HashLongestMatch {
enum { kHashMapSize = 2 << kBucketBits };
static const size_t kMaxNumMatches = 64 + (1 << kBlockBits);
private:
// Number of hash buckets.
static const uint32_t kBucketSize = 1 << kBucketBits;
@ -628,6 +632,235 @@ class HashLongestMatch {
size_t num_dict_matches_;
};
// A (forgetful) hash table where each hash bucket contains a binary tree of
// sequences whose first 4 bytes share the same hash code.
// Each sequence is kMaxTreeCompLength long and is identified by its starting
// position in the input data. The binary tree is sorted by the lexicographic
// order of the sequences, and it is also a max-heap with respect to the
// starting positions.
class HashToBinaryTree {
public:
HashToBinaryTree() : forest_(NULL) {
Reset();
}
~HashToBinaryTree() {
delete[] forest_;
}
void Reset() {
need_init_ = true;
}
void Init(int lgwin, size_t position, size_t bytes, bool is_last) {
if (need_init_) {
window_mask_ = (1u << lgwin) - 1u;
invalid_pos_ = static_cast<uint32_t>(-window_mask_);
for (uint32_t i = 0; i < kBucketSize; i++) {
buckets_[i] = invalid_pos_;
}
size_t num_nodes = (position == 0 && is_last) ? bytes : window_mask_ + 1;
forest_ = new uint32_t[2 * num_nodes];
need_init_ = false;
}
}
// Finds all backward matches of &data[cur_ix & ring_buffer_mask] up to the
// length of max_length and stores the position cur_ix in the hash table.
//
// Sets *num_matches to the number of matches found, and stores the found
// matches in matches[0] to matches[*num_matches - 1]. The matches will be
// sorted by strictly increasing length and (non-strictly) increasing
// distance.
size_t FindAllMatches(const uint8_t* data,
const size_t ring_buffer_mask,
const size_t cur_ix,
const size_t max_length,
const size_t max_backward,
BackwardMatch* matches) {
BackwardMatch* const orig_matches = matches;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
size_t best_len = 1;
size_t stop = cur_ix - 64;
if (cur_ix < 64) { stop = 0; }
for (size_t i = cur_ix - 1; i > stop && best_len <= 2; --i) {
size_t prev_ix = i;
const size_t backward = cur_ix - prev_ix;
if (PREDICT_FALSE(backward > max_backward)) {
break;
}
prev_ix &= ring_buffer_mask;
if (data[cur_ix_masked] != data[prev_ix] ||
data[cur_ix_masked + 1] != data[prev_ix + 1]) {
continue;
}
const size_t len =
FindMatchLengthWithLimit(&data[prev_ix], &data[cur_ix_masked],
max_length);
if (len > best_len) {
best_len = len;
*matches++ = BackwardMatch(backward, len);
}
}
if (best_len < max_length) {
matches = StoreAndFindMatches(data, cur_ix, ring_buffer_mask,
max_length, &best_len, matches);
}
std::vector<uint32_t> dict_matches(kMaxDictionaryMatchLen + 1,
kInvalidMatch);
size_t minlen = std::max<size_t>(4, best_len + 1);
if (FindAllStaticDictionaryMatches(&data[cur_ix_masked], minlen, max_length,
&dict_matches[0])) {
size_t maxlen = std::min<size_t>(kMaxDictionaryMatchLen, max_length);
for (size_t l = minlen; l <= maxlen; ++l) {
uint32_t dict_id = dict_matches[l];
if (dict_id < kInvalidMatch) {
*matches++ = BackwardMatch(max_backward + (dict_id >> 5) + 1, l,
dict_id & 31);
}
}
}
return static_cast<size_t>(matches - orig_matches);
}
// Stores the hash of the next 4 bytes and re-roots the binary tree at the
// current sequence, without returning any matches.
void Store(const uint8_t* data,
const size_t ring_buffer_mask,
const size_t cur_ix,
const size_t max_length) {
size_t best_len = 0;
StoreAndFindMatches(data, cur_ix, ring_buffer_mask, max_length,
&best_len, NULL);
}
static const size_t kMaxNumMatches = 64 + kMaxTreeSearchDepth;
private:
// Stores the hash of the next 4 bytes and in a single tree-traversal, the
// hash bucket's binary tree is searched for matches and is re-rooted at the
// current position.
//
// If less than kMaxTreeCompLength data is available, the hash bucket of the
// current position is searched for matches, but the state of the hash table
// is not changed, since we can not know the final sorting order of the
// current (incomplete) sequence.
//
// This function must be called with increasing cur_ix positions.
BackwardMatch* StoreAndFindMatches(const uint8_t* const __restrict data,
const size_t cur_ix,
const size_t ring_buffer_mask,
const size_t max_length,
size_t* const __restrict best_len,
BackwardMatch* __restrict matches) {
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
const size_t max_backward = window_mask_ - 15;
const size_t max_comp_len = std::min(max_length, kMaxTreeCompLength);
const bool reroot_tree = max_length >= kMaxTreeCompLength;
const uint32_t key = HashBytes(&data[cur_ix_masked]);
size_t prev_ix = buckets_[key];
// The forest index of the rightmost node of the left subtree of the new
// root, updated as we traverse and reroot the tree of the hash bucket.
size_t node_left = LeftChildIndex(cur_ix);
// The forest index of the leftmost node of the right subtree of the new
// root, updated as we traverse and reroot the tree of the hash bucket.
size_t node_right = RightChildIndex(cur_ix);
// The match length of the rightmost node of the left subtree of the new
// root, updated as we traverse and reroot the tree of the hash bucket.
size_t best_len_left = 0;
// The match length of the leftmost node of the right subtree of the new
// root, updated as we traverse and reroot the tree of the hash bucket.
size_t best_len_right = 0;
if (reroot_tree) {
buckets_[key] = static_cast<uint32_t>(cur_ix);
}
for (size_t depth_remaining = kMaxTreeSearchDepth; ; --depth_remaining) {
const size_t backward = cur_ix - prev_ix;
const size_t prev_ix_masked = prev_ix & ring_buffer_mask;
if (backward == 0 || backward > max_backward || depth_remaining == 0) {
if (reroot_tree) {
forest_[node_left] = invalid_pos_;
forest_[node_right] = invalid_pos_;
}
break;
}
const size_t cur_len = std::min(best_len_left, best_len_right);
const size_t len = cur_len +
FindMatchLengthWithLimit(&data[cur_ix_masked + cur_len],
&data[prev_ix_masked + cur_len],
max_length - cur_len);
if (len > *best_len) {
*best_len = len;
if (matches) {
*matches++ = BackwardMatch(backward, len);
}
if (len >= max_comp_len) {
if (reroot_tree) {
forest_[node_left] = forest_[LeftChildIndex(prev_ix)];
forest_[node_right] = forest_[RightChildIndex(prev_ix)];
}
break;
}
}
if (data[cur_ix_masked + len] > data[prev_ix_masked + len]) {
best_len_left = len;
if (reroot_tree) {
forest_[node_left] = static_cast<uint32_t>(prev_ix);
}
node_left = RightChildIndex(prev_ix);
prev_ix = forest_[node_left];
} else {
best_len_right = len;
if (reroot_tree) {
forest_[node_right] = static_cast<uint32_t>(prev_ix);
}
node_right = LeftChildIndex(prev_ix);
prev_ix = forest_[node_right];
}
}
return matches;
}
inline size_t LeftChildIndex(const size_t pos) {
return 2 * (pos & window_mask_);
}
inline size_t RightChildIndex(const size_t pos) {
return 2 * (pos & window_mask_) + 1;
}
static uint32_t HashBytes(const uint8_t *data) {
uint32_t h = BROTLI_UNALIGNED_LOAD32(data) * kHashMul32;
// The higher bits contain more mixture from the multiplication,
// so we take our results from there.
return h >> (32 - kBucketBits);
}
static const int kBucketBits = 17;
static const size_t kBucketSize = 1 << kBucketBits;
// The window size minus 1
size_t window_mask_;
// Hash table that maps the 4-byte hashes of the sequence to the last
// position where this hash was found, which is the root of the binary
// tree of sequences that share this hash bucket.
uint32_t buckets_[kBucketSize];
// The union of the binary trees of each hash bucket. The root of the tree
// corresponding to a hash is a sequence starting at buckets_[hash] and
// the left and right children of a sequence starting at pos are
// forest_[2 * pos] and forest_[2 * pos + 1].
uint32_t* forest_;
// A position used to mark a non-existent sequence, i.e. a tree is empty if
// its root is at invalid_pos_ and a node is a leaf if both its children
// are at invalid_pos_.
uint32_t invalid_pos_;
bool need_init_;
};
struct Hashers {
// For kBucketSweep == 1, enabling the dictionary lookup makes compression
// a little faster (0.5% - 1%) and it compresses 0.15% better on small text
@ -640,9 +873,10 @@ struct Hashers {
typedef HashLongestMatch<15, 6, 10> H7;
typedef HashLongestMatch<15, 7, 10> H8;
typedef HashLongestMatch<15, 8, 16> H9;
typedef HashToBinaryTree H10;
Hashers() : hash_h2(0), hash_h3(0), hash_h4(0), hash_h5(0),
hash_h6(0), hash_h7(0), hash_h8(0), hash_h9(0) {}
hash_h6(0), hash_h7(0), hash_h8(0), hash_h9(0), hash_h10(0) {}
~Hashers() {
delete hash_h2;
@ -653,6 +887,7 @@ struct Hashers {
delete hash_h7;
delete hash_h8;
delete hash_h9;
delete hash_h10;
}
void Init(int type) {
@ -665,6 +900,7 @@ struct Hashers {
case 7: hash_h7 = new H7; break;
case 8: hash_h8 = new H8; break;
case 9: hash_h9 = new H9; break;
case 10: hash_h10 = new H10; break;
default: break;
}
}
@ -679,7 +915,7 @@ struct Hashers {
// Custom LZ77 window.
void PrependCustomDictionary(
int type, const size_t size, const uint8_t* dict) {
int type, int lgwin, const size_t size, const uint8_t* dict) {
switch (type) {
case 2: WarmupHash(size, dict, hash_h2); break;
case 3: WarmupHash(size, dict, hash_h3); break;
@ -689,6 +925,13 @@ struct Hashers {
case 7: WarmupHash(size, dict, hash_h7); break;
case 8: WarmupHash(size, dict, hash_h8); break;
case 9: WarmupHash(size, dict, hash_h9); break;
case 10:
hash_h10->Init(lgwin, 0, size, false);
for (size_t i = 0; i + kMaxTreeCompLength - 1 < size; ++i) {
hash_h10->Store(dict, std::numeric_limits<size_t>::max(),
i, size - i);
}
break;
default: break;
}
}
@ -702,6 +945,7 @@ struct Hashers {
H7* hash_h7;
H8* hash_h8;
H9* hash_h9;
H10* hash_h10;
};
} // namespace brotli