package brotli import ( "encoding/binary" "fmt" ) type hasherCommon struct { params hasherParams is_prepared_ bool dict_num_lookups uint dict_num_matches uint } func (h *hasherCommon) Common() *hasherCommon { return h } type hasherHandle interface { Common() *hasherCommon Initialize(params *encoderParams) Prepare(one_shot bool, input_size uint, data []byte) StitchToPreviousBlock(num_bytes uint, position uint, ringbuffer []byte, ringbuffer_mask uint) HashTypeLength() uint StoreLookahead() uint PrepareDistanceCache(distance_cache []int) 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) StoreRange(data []byte, mask uint, ix_start uint, ix_end uint) Store(data []byte, mask uint, ix uint) } const kCutoffTransformsCount uint32 = 10 /* 0, 12, 27, 23, 42, 63, 56, 48, 59, 64 */ /* 0+0, 4+8, 8+19, 12+11, 16+26, 20+43, 24+32, 28+20, 32+27, 36+28 */ const kCutoffTransforms uint64 = 0x071B520ADA2D3200 type hasherSearchResult struct { len uint distance uint score uint len_code_delta int } /* kHashMul32 multiplier has these properties: * The multiplier must be odd. Otherwise we may lose the highest bit. * No long streaks of ones or zeros. * 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. */ const kHashMul32 uint32 = 0x1E35A7BD const kHashMul64 uint64 = 0x1E35A7BD1E35A7BD const kHashMul64Long uint64 = 0x1FE35A7BD3579BD3 func hash14(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 - 14) } func prepareDistanceCache(distance_cache []int, num_distances int) { if num_distances > 4 { var last_distance int = distance_cache[0] distance_cache[4] = last_distance - 1 distance_cache[5] = last_distance + 1 distance_cache[6] = last_distance - 2 distance_cache[7] = last_distance + 2 distance_cache[8] = last_distance - 3 distance_cache[9] = last_distance + 3 if num_distances > 10 { var next_last_distance int = distance_cache[1] distance_cache[10] = next_last_distance - 1 distance_cache[11] = next_last_distance + 1 distance_cache[12] = next_last_distance - 2 distance_cache[13] = next_last_distance + 2 distance_cache[14] = next_last_distance - 3 distance_cache[15] = next_last_distance + 3 } } } const literalByteScore = 135 const distanceBitPenalty = 30 /* Score must be positive after applying maximal penalty. */ const scoreBase = (distanceBitPenalty * 8 * 8) /* Usually, we always choose the longest backward reference. This function allows for the exception of that rule. If we choose a backward reference that is further away, it will usually be coded with more bits. We approximate this by assuming log2(distance). If the distance can be expressed in terms of the last four distances, we use some heuristic constants to estimate the bits cost. For the first up to four literals we use the bit cost of the literals from the literal cost model, after that we use the average bit cost of the cost model. This function is used to sometimes discard a longer backward reference when it is not much longer and the bit cost for encoding it is more than the saved literals. backward_reference_offset MUST be positive. */ func backwardReferenceScore(copy_length uint, backward_reference_offset uint) uint { return scoreBase + literalByteScore*uint(copy_length) - distanceBitPenalty*uint(log2FloorNonZero(backward_reference_offset)) } func backwardReferenceScoreUsingLastDistance(copy_length uint) uint { return literalByteScore*uint(copy_length) + scoreBase + 15 } func backwardReferencePenaltyUsingLastDistance(distance_short_code uint) uint { return uint(39) + ((0x1CA10 >> (distance_short_code & 0xE)) & 0xE) } func testStaticDictionaryItem(dictionary *encoderDictionary, item uint, data []byte, max_length uint, max_backward uint, max_distance uint, out *hasherSearchResult) bool { var len uint var word_idx uint var offset uint var matchlen uint var backward uint var score uint len = item & 0x1F word_idx = item >> 5 offset = uint(dictionary.words.offsets_by_length[len]) + len*word_idx if len > max_length { return false } matchlen = findMatchLengthWithLimit(data, dictionary.words.data[offset:], uint(len)) if matchlen+uint(dictionary.cutoffTransformsCount) <= len || matchlen == 0 { return false } { var cut uint = len - matchlen var transform_id uint = (cut << 2) + uint((dictionary.cutoffTransforms>>(cut*6))&0x3F) backward = max_backward + 1 + word_idx + (transform_id << dictionary.words.size_bits_by_length[len]) } if backward > max_distance { return false } score = backwardReferenceScore(matchlen, backward) if score < out.score { return false } out.len = matchlen out.len_code_delta = int(len) - int(matchlen) out.distance = backward out.score = score return true } func searchInStaticDictionary(dictionary *encoderDictionary, handle hasherHandle, data []byte, max_length uint, max_backward uint, max_distance uint, out *hasherSearchResult, shallow bool) { var key uint var i uint var self *hasherCommon = handle.Common() if self.dict_num_matches < self.dict_num_lookups>>7 { return } key = uint(hash14(data) << 1) for i = 0; ; (func() { i++; key++ })() { var tmp uint if shallow { tmp = 1 } else { tmp = 2 } if i >= tmp { break } var item uint = uint(dictionary.hash_table[key]) self.dict_num_lookups++ if item != 0 { var item_matches bool = testStaticDictionaryItem(dictionary, item, data, max_length, max_backward, max_distance, out) if item_matches { self.dict_num_matches++ } } } } type backwardMatch struct { distance uint32 length_and_code uint32 } func initBackwardMatch(self *backwardMatch, dist uint, len uint) { self.distance = uint32(dist) self.length_and_code = uint32(len << 5) } func initDictionaryBackwardMatch(self *backwardMatch, dist uint, len uint, len_code uint) { self.distance = uint32(dist) var tmp uint if len == len_code { tmp = 0 } else { tmp = len_code } self.length_and_code = uint32(len<<5 | tmp) } func backwardMatchLength(self *backwardMatch) uint { return uint(self.length_and_code >> 5) } func backwardMatchLengthCode(self *backwardMatch) uint { var code uint = uint(self.length_and_code) & 31 if code != 0 { return code } else { return backwardMatchLength(self) } } func hasherReset(handle hasherHandle) { if handle == nil { return } handle.Common().is_prepared_ = false } func newHasher(typ int) hasherHandle { switch typ { case 2: return &hashLongestMatchQuickly{ bucketBits: 16, bucketSweep: 1, hashLen: 5, useDictionary: true, } case 3: return &hashLongestMatchQuickly{ bucketBits: 16, bucketSweep: 2, hashLen: 5, useDictionary: false, } case 4: return &hashLongestMatchQuickly{ bucketBits: 17, bucketSweep: 4, hashLen: 5, useDictionary: true, } case 5: return new(h5) case 6: return new(h6) case 10: return new(h10) case 35: return &hashComposite{ ha: newHasher(3), hb: &hashRolling{jump: 4}, } case 40: return &hashForgetfulChain{ bucketBits: 15, numBanks: 1, bankBits: 16, numLastDistancesToCheck: 4, } case 41: return &hashForgetfulChain{ bucketBits: 15, numBanks: 1, bankBits: 16, numLastDistancesToCheck: 10, } case 42: return &hashForgetfulChain{ bucketBits: 15, numBanks: 512, bankBits: 9, numLastDistancesToCheck: 16, } case 54: return &hashLongestMatchQuickly{ bucketBits: 20, bucketSweep: 4, hashLen: 7, useDictionary: false, } case 55: return &hashComposite{ ha: newHasher(54), hb: &hashRolling{jump: 4}, } case 65: return &hashComposite{ ha: newHasher(6), hb: &hashRolling{jump: 1}, } } panic(fmt.Sprintf("unknown hasher type: %d", typ)) } func hasherSetup(handle *hasherHandle, params *encoderParams, data []byte, position uint, input_size uint, is_last bool) { var self hasherHandle = nil var common *hasherCommon = nil var one_shot bool = (position == 0 && is_last) if *handle == nil { chooseHasher(params, ¶ms.hasher) self = newHasher(params.hasher.type_) *handle = self common = self.Common() common.params = params.hasher self.Initialize(params) } self = *handle common = self.Common() if !common.is_prepared_ { self.Prepare(one_shot, input_size, data) if position == 0 { common.dict_num_lookups = 0 common.dict_num_matches = 0 } common.is_prepared_ = true } } func initOrStitchToPreviousBlock(handle *hasherHandle, data []byte, mask uint, params *encoderParams, position uint, input_size uint, is_last bool) { var self hasherHandle hasherSetup(handle, params, data, position, input_size, is_last) self = *handle self.StitchToPreviousBlock(input_size, position, data, mask) }