246 lines
7.4 KiB
Go
246 lines
7.4 KiB
Go
package brotli
|
|
|
|
/* 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 to the data seen by the compressor, to
|
|
help create backward references to previous data.
|
|
|
|
Hashes are stored in chains which are bucketed to groups. Group of chains
|
|
share a storage "bank". When more than "bank size" chain nodes are added,
|
|
oldest nodes are replaced; this way several chains may share a tail. */
|
|
func HashTypeLengthH41() uint {
|
|
return 4
|
|
}
|
|
|
|
func StoreLookaheadH41() uint {
|
|
return 4
|
|
}
|
|
|
|
/* HashBytes is the function that chooses the bucket to place the address in.*/
|
|
func HashBytesH41(data []byte) uint {
|
|
var h uint32 = BROTLI_UNALIGNED_LOAD32LE(data) * kHashMul32
|
|
|
|
/* The higher bits contain more mixture from the multiplication,
|
|
so we take our results from there. */
|
|
return uint(h >> (32 - 15))
|
|
}
|
|
|
|
type SlotH41 struct {
|
|
delta uint16
|
|
next uint16
|
|
}
|
|
|
|
type BankH41 struct {
|
|
slots [1 << 16]SlotH41
|
|
}
|
|
|
|
type H41 struct {
|
|
addr [1 << 15]uint32
|
|
head [1 << 15]uint16
|
|
tiny_hash [65536]byte
|
|
banks [1]BankH41
|
|
free_slot_idx [1]uint16
|
|
max_hops uint
|
|
}
|
|
|
|
func SelfH41(handle HasherHandle) *H41 {
|
|
return handle.extra.(*H41)
|
|
}
|
|
|
|
func InitializeH41(handle HasherHandle, params *BrotliEncoderParams) {
|
|
handle.extra = new(H41)
|
|
var tmp uint
|
|
if params.quality > 6 {
|
|
tmp = 7
|
|
} else {
|
|
tmp = 8
|
|
}
|
|
SelfH41(handle).max_hops = tmp << uint(params.quality-4)
|
|
}
|
|
|
|
func PrepareH41(handle HasherHandle, one_shot bool, input_size uint, data []byte) {
|
|
var self *H41 = SelfH41(handle)
|
|
var partial_prepare_threshold uint = (1 << 15) >> 6
|
|
/* Partial preparation is 100 times slower (per socket). */
|
|
if one_shot && input_size <= partial_prepare_threshold {
|
|
var i uint
|
|
for i = 0; i < input_size; i++ {
|
|
var bucket uint = HashBytesH41(data[i:])
|
|
|
|
/* See InitEmpty comment. */
|
|
self.addr[bucket] = 0xCCCCCCCC
|
|
|
|
self.head[bucket] = 0xCCCC
|
|
}
|
|
} else {
|
|
/* Fill |addr| array with 0xCCCCCCCC value. Because of wrapping, position
|
|
processed by hasher never reaches 3GB + 64M; this makes all new chains
|
|
to be terminated after the first node. */
|
|
var i int
|
|
for i = 0; i < len(self.addr); i++ {
|
|
self.addr[i] = 0xCCCCCCCC
|
|
}
|
|
|
|
self.head = [1 << 15]uint16{}
|
|
}
|
|
|
|
self.tiny_hash = [65536]byte{}
|
|
self.free_slot_idx = [1]uint16{}
|
|
}
|
|
|
|
/* Look at 4 bytes at &data[ix & mask]. Compute a hash from these, and prepend
|
|
node to corresponding chain; also update tiny_hash for current position. */
|
|
func StoreH41(handle HasherHandle, data []byte, mask uint, ix uint) {
|
|
var self *H41 = SelfH41(handle)
|
|
var key uint = HashBytesH41(data[ix&mask:])
|
|
var bank uint = key & (1 - 1)
|
|
var idx uint
|
|
idx = uint(self.free_slot_idx[bank]) & ((1 << 16) - 1)
|
|
self.free_slot_idx[bank]++
|
|
var delta uint = ix - uint(self.addr[key])
|
|
self.tiny_hash[uint16(ix)] = byte(key)
|
|
if delta > 0xFFFF {
|
|
delta = 0xFFFF
|
|
}
|
|
self.banks[bank].slots[idx].delta = uint16(delta)
|
|
self.banks[bank].slots[idx].next = self.head[key]
|
|
self.addr[key] = uint32(ix)
|
|
self.head[key] = uint16(idx)
|
|
}
|
|
|
|
func StoreRangeH41(handle HasherHandle, data []byte, mask uint, ix_start uint, ix_end uint) {
|
|
var i uint
|
|
for i = ix_start; i < ix_end; i++ {
|
|
StoreH41(handle, data, mask, i)
|
|
}
|
|
}
|
|
|
|
func StitchToPreviousBlockH41(handle HasherHandle, num_bytes uint, position uint, ringbuffer []byte, ring_buffer_mask uint) {
|
|
if num_bytes >= HashTypeLengthH41()-1 && position >= 3 {
|
|
/* Prepare the hashes for three last bytes of the last write.
|
|
These could not be calculated before, since they require knowledge
|
|
of both the previous and the current block. */
|
|
StoreH41(handle, ringbuffer, ring_buffer_mask, position-3)
|
|
|
|
StoreH41(handle, ringbuffer, ring_buffer_mask, position-2)
|
|
StoreH41(handle, ringbuffer, ring_buffer_mask, position-1)
|
|
}
|
|
}
|
|
|
|
func PrepareDistanceCacheH41(handle HasherHandle, distance_cache []int) {
|
|
PrepareDistanceCache(distance_cache, 10)
|
|
}
|
|
|
|
/* Find a longest backward match of &data[cur_ix] up to the length of
|
|
max_length and stores the position cur_ix in the hash table.
|
|
|
|
REQUIRES: PrepareDistanceCacheH41 must be invoked for current distance cache
|
|
values; if this method is invoked repeatedly with the same distance
|
|
cache values, it is enough to invoke PrepareDistanceCacheH41 once.
|
|
|
|
Does not look for matches longer than max_length.
|
|
Does not look for matches further away than max_backward.
|
|
Writes the best match into |out|.
|
|
|out|->score is updated only if a better match is found. */
|
|
func FindLongestMatchH41(handle HasherHandle, dictionary *BrotliEncoderDictionary, 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) {
|
|
var self *H41 = SelfH41(handle)
|
|
var cur_ix_masked uint = cur_ix & ring_buffer_mask
|
|
var min_score uint = out.score
|
|
var best_score uint = out.score
|
|
var best_len uint = out.len
|
|
var i uint
|
|
var key uint = HashBytesH41(data[cur_ix_masked:])
|
|
var tiny_hash byte = byte(key)
|
|
/* Don't accept a short copy from far away. */
|
|
out.len = 0
|
|
|
|
out.len_code_delta = 0
|
|
|
|
/* Try last distance first. */
|
|
for i = 0; i < 10; i++ {
|
|
var backward uint = uint(distance_cache[i])
|
|
var prev_ix uint = (cur_ix - backward)
|
|
|
|
/* For distance code 0 we want to consider 2-byte matches. */
|
|
if i > 0 && self.tiny_hash[uint16(prev_ix)] != tiny_hash {
|
|
continue
|
|
}
|
|
if prev_ix >= cur_ix || backward > max_backward {
|
|
continue
|
|
}
|
|
|
|
prev_ix &= ring_buffer_mask
|
|
{
|
|
var len uint = FindMatchLengthWithLimit(data[prev_ix:], data[cur_ix_masked:], max_length)
|
|
if len >= 2 {
|
|
var score uint = BackwardReferenceScoreUsingLastDistance(uint(len))
|
|
if best_score < score {
|
|
if i != 0 {
|
|
score -= BackwardReferencePenaltyUsingLastDistance(i)
|
|
}
|
|
if best_score < score {
|
|
best_score = score
|
|
best_len = uint(len)
|
|
out.len = best_len
|
|
out.distance = backward
|
|
out.score = best_score
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
{
|
|
var bank uint = key & (1 - 1)
|
|
var backward uint = 0
|
|
var hops uint = self.max_hops
|
|
var delta uint = cur_ix - uint(self.addr[key])
|
|
var slot uint = uint(self.head[key])
|
|
for {
|
|
tmp7 := hops
|
|
hops--
|
|
if tmp7 == 0 {
|
|
break
|
|
}
|
|
var prev_ix uint
|
|
var last uint = slot
|
|
backward += delta
|
|
if backward > max_backward {
|
|
break
|
|
}
|
|
prev_ix = (cur_ix - backward) & ring_buffer_mask
|
|
slot = uint(self.banks[bank].slots[last].next)
|
|
delta = uint(self.banks[bank].slots[last].delta)
|
|
if cur_ix_masked+best_len > ring_buffer_mask || prev_ix+best_len > ring_buffer_mask || data[cur_ix_masked+best_len] != data[prev_ix+best_len] {
|
|
continue
|
|
}
|
|
{
|
|
var len uint = FindMatchLengthWithLimit(data[prev_ix:], data[cur_ix_masked:], max_length)
|
|
if len >= 4 {
|
|
/* Comparing for >= 3 does not change the semantics, but just saves
|
|
for a few unnecessary binary logarithms in backward reference
|
|
score, since we are not interested in such short matches. */
|
|
var score uint = BackwardReferenceScore(uint(len), backward)
|
|
if best_score < score {
|
|
best_score = score
|
|
best_len = uint(len)
|
|
out.len = best_len
|
|
out.distance = backward
|
|
out.score = best_score
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
StoreH41(handle, data, ring_buffer_mask, cur_ix)
|
|
}
|
|
|
|
if out.score == min_score {
|
|
SearchInStaticDictionary(dictionary, handle, data[cur_ix_masked:], max_length, max_backward+gap, max_distance, out, false)
|
|
}
|
|
}
|