brotli/h10.go

289 lines
9.5 KiB
Go

package brotli
import "encoding/binary"
/* NOLINT(build/header_guard) */
/* Copyright 2016 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* 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 128 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. */
func (*h10) HashTypeLength() uint {
return 4
}
func (*h10) StoreLookahead() uint {
return 128
}
func hashBytesH10(data []byte) uint32 {
var h uint32 = binary.LittleEndian.Uint32(data) * kHashMul32
/* The higher bits contain more mixture from the multiplication,
so we take our results from there. */
return h >> (32 - 17)
}
type h10 struct {
hasherCommon
window_mask_ uint
buckets_ [1 << 17]uint32
invalid_pos_ uint32
forest []uint32
}
func (h *h10) Initialize(params *encoderParams) {
h.window_mask_ = (1 << params.lgwin) - 1
h.invalid_pos_ = uint32(0 - h.window_mask_)
var num_nodes uint = uint(1) << params.lgwin
h.forest = make([]uint32, 2*num_nodes)
}
func (h *h10) Prepare(one_shot bool, input_size uint, data []byte) {
var invalid_pos uint32 = h.invalid_pos_
var i uint32
for i = 0; i < 1<<17; i++ {
h.buckets_[i] = invalid_pos
}
}
func leftChildIndexH10(self *h10, pos uint) uint {
return 2 * (pos & self.window_mask_)
}
func rightChildIndexH10(self *h10, pos uint) uint {
return 2*(pos&self.window_mask_) + 1
}
/* 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 128 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. */
func storeAndFindMatchesH10(self *h10, data []byte, cur_ix uint, ring_buffer_mask uint, max_length uint, max_backward uint, best_len *uint, matches []backwardMatch) []backwardMatch {
var cur_ix_masked uint = cur_ix & ring_buffer_mask
var max_comp_len uint = brotli_min_size_t(max_length, 128)
var should_reroot_tree bool = (max_length >= 128)
var key uint32 = hashBytesH10(data[cur_ix_masked:])
var forest []uint32 = self.forest
var prev_ix uint = uint(self.buckets_[key])
var node_left uint = leftChildIndexH10(self, cur_ix)
var node_right uint = rightChildIndexH10(self, cur_ix)
var best_len_left uint = 0
var best_len_right uint = 0
var depth_remaining uint
/* The forest index of the rightmost node of the left subtree of the new
root, updated as we traverse and re-root the tree of the hash bucket. */
/* The forest index of the leftmost node of the right subtree of the new
root, updated as we traverse and re-root the tree of the hash bucket. */
/* The match length of the rightmost node of the left subtree of the new
root, updated as we traverse and re-root the tree of the hash bucket. */
/* The match length of the leftmost node of the right subtree of the new
root, updated as we traverse and re-root the tree of the hash bucket. */
if should_reroot_tree {
self.buckets_[key] = uint32(cur_ix)
}
for depth_remaining = 64; ; depth_remaining-- {
var backward uint = cur_ix - prev_ix
var prev_ix_masked uint = prev_ix & ring_buffer_mask
if backward == 0 || backward > max_backward || depth_remaining == 0 {
if should_reroot_tree {
forest[node_left] = self.invalid_pos_
forest[node_right] = self.invalid_pos_
}
break
}
{
var cur_len uint = brotli_min_size_t(best_len_left, best_len_right)
var len uint
assert(cur_len <= 128)
len = cur_len + findMatchLengthWithLimit(data[cur_ix_masked+cur_len:], data[prev_ix_masked+cur_len:], max_length-cur_len)
if matches != nil && len > *best_len {
*best_len = uint(len)
initBackwardMatch(&matches[0], backward, uint(len))
matches = matches[1:]
}
if len >= max_comp_len {
if should_reroot_tree {
forest[node_left] = forest[leftChildIndexH10(self, prev_ix)]
forest[node_right] = forest[rightChildIndexH10(self, prev_ix)]
}
break
}
if data[cur_ix_masked+len] > data[prev_ix_masked+len] {
best_len_left = uint(len)
if should_reroot_tree {
forest[node_left] = uint32(prev_ix)
}
node_left = rightChildIndexH10(self, prev_ix)
prev_ix = uint(forest[node_left])
} else {
best_len_right = uint(len)
if should_reroot_tree {
forest[node_right] = uint32(prev_ix)
}
node_right = leftChildIndexH10(self, prev_ix)
prev_ix = uint(forest[node_right])
}
}
}
return 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]. The matches will be
sorted by strictly increasing length and (non-strictly) increasing
distance. */
func findAllMatchesH10(handle *h10, dictionary *encoderDictionary, data []byte, ring_buffer_mask uint, cur_ix uint, max_length uint, max_backward uint, gap uint, params *encoderParams, matches []backwardMatch) uint {
var orig_matches []backwardMatch = matches
var cur_ix_masked uint = cur_ix & ring_buffer_mask
var best_len uint = 1
var short_match_max_backward uint
if params.quality != hqZopflificationQuality {
short_match_max_backward = 16
} else {
short_match_max_backward = 64
}
var stop uint = cur_ix - short_match_max_backward
var dict_matches [maxStaticDictionaryMatchLen + 1]uint32
var i uint
if cur_ix < short_match_max_backward {
stop = 0
}
for i = cur_ix - 1; i > stop && best_len <= 2; i-- {
var prev_ix uint = i
var backward uint = cur_ix - prev_ix
if 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
}
{
var len uint = findMatchLengthWithLimit(data[prev_ix:], data[cur_ix_masked:], max_length)
if len > best_len {
best_len = uint(len)
initBackwardMatch(&matches[0], backward, uint(len))
matches = matches[1:]
}
}
}
if best_len < max_length {
matches = storeAndFindMatchesH10(handle, data, cur_ix, ring_buffer_mask, max_length, max_backward, &best_len, matches)
}
for i = 0; i <= maxStaticDictionaryMatchLen; i++ {
dict_matches[i] = kInvalidMatch
}
{
var minlen uint = brotli_max_size_t(4, best_len+1)
if findAllStaticDictionaryMatches(dictionary, data[cur_ix_masked:], minlen, max_length, dict_matches[0:]) {
var maxlen uint = brotli_min_size_t(maxStaticDictionaryMatchLen, max_length)
var l uint
for l = minlen; l <= maxlen; l++ {
var dict_id uint32 = dict_matches[l]
if dict_id < kInvalidMatch {
var distance uint = max_backward + gap + uint(dict_id>>5) + 1
if distance <= params.dist.max_distance {
initDictionaryBackwardMatch(&matches[0], distance, l, uint(dict_id&31))
matches = matches[1:]
}
}
}
}
}
return uint(-cap(matches) + cap(orig_matches))
}
/* Stores the hash of the next 4 bytes and re-roots the binary tree at the
current sequence, without returning any matches.
REQUIRES: ix + 128 <= end-of-current-block */
func (h *h10) Store(data []byte, mask uint, ix uint) {
var max_backward uint = h.window_mask_ - windowGap + 1
/* Maximum distance is window size - 16, see section 9.1. of the spec. */
storeAndFindMatchesH10(h, data, ix, mask, 128, max_backward, nil, nil)
}
func (h *h10) StoreRange(data []byte, mask uint, ix_start uint, ix_end uint) {
var i uint = ix_start
var j uint = ix_start
if ix_start+63 <= ix_end {
i = ix_end - 63
}
if ix_start+512 <= i {
for ; j < i; j += 8 {
h.Store(data, mask, j)
}
}
for ; i < ix_end; i++ {
h.Store(data, mask, i)
}
}
func (h *h10) StitchToPreviousBlock(num_bytes uint, position uint, ringbuffer []byte, ringbuffer_mask uint) {
if num_bytes >= h.HashTypeLength()-1 && position >= 128 {
var i_start uint = position - 128 + 1
var i_end uint = brotli_min_size_t(position, i_start+num_bytes)
/* Store the last `128 - 1` positions in the hasher.
These could not be calculated before, since they require knowledge
of both the previous and the current block. */
var i uint
for i = i_start; i < i_end; i++ {
/* Maximum distance is window size - 16, see section 9.1. of the spec.
Furthermore, we have to make sure that we don't look further back
from the start of the next block than the window size, otherwise we
could access already overwritten areas of the ring-buffer. */
var max_backward uint = h.window_mask_ - brotli_max_size_t(windowGap-1, position-i)
/* We know that i + 128 <= position + num_bytes, i.e. the
end of the current block and that we have at least
128 tail in the ring-buffer. */
storeAndFindMatchesH10(h, ringbuffer, i, ringbuffer_mask, 128, max_backward, nil, nil)
}
}
}
/* MAX_NUM_MATCHES == 64 + MAX_TREE_SEARCH_DEPTH */
const maxNumMatchesH10 = 128
func (*h10) FindLongestMatch(dictionary *encoderDictionary, data []byte, ring_buffer_mask uint, distance_cache []int, cur_ix uint, max_length uint, max_backward uint, gap uint, max_distance uint, out *hasherSearchResult) {
panic("unimplemented")
}
func (*h10) PrepareDistanceCache(distance_cache []int) {
panic("unimplemented")
}