package brotli /* Copyright 2013 Google Inc. All Rights Reserved. Distributed under MIT license. See file LICENSE for detail or copy at https://opensource.org/licenses/MIT */ const ( decoderResultError = 0 decoderResultSuccess = 1 decoderResultNeedsMoreInput = 2 decoderResultNeedsMoreOutput = 3 ) /** * Error code for detailed logging / production debugging. * * See ::BrotliDecoderGetErrorCode and ::BROTLI_LAST_ERROR_CODE. */ const ( decoderNoError = 0 decoderSuccess = 1 decoderNeedsMoreInput = 2 decoderNeedsMoreOutput = 3 decoderErrorFormatExuberantNibble = -1 decoderErrorFormatReserved = -2 decoderErrorFormatExuberantMetaNibble = -3 decoderErrorFormatSimpleHuffmanAlphabet = -4 decoderErrorFormatSimpleHuffmanSame = -5 decoderErrorFormatClSpace = -6 decoderErrorFormatHuffmanSpace = -7 decoderErrorFormatContextMapRepeat = -8 decoderErrorFormatBlockLength1 = -9 decoderErrorFormatBlockLength2 = -10 decoderErrorFormatTransform = -11 decoderErrorFormatDictionary = -12 decoderErrorFormatWindowBits = -13 decoderErrorFormatPadding1 = -14 decoderErrorFormatPadding2 = -15 decoderErrorFormatDistance = -16 decoderErrorDictionaryNotSet = -19 decoderErrorInvalidArguments = -20 decoderErrorAllocContextModes = -21 decoderErrorAllocTreeGroups = -22 decoderErrorAllocContextMap = -25 decoderErrorAllocRingBuffer1 = -26 decoderErrorAllocRingBuffer2 = -27 decoderErrorAllocBlockTypeTrees = -30 decoderErrorUnreachable = -31 ) /** * The value of the last error code, negative integer. * * All other error code values are in the range from ::lastErrorCode * to @c -1. There are also 4 other possible non-error codes @c 0 .. @c 3 in * ::BrotliDecoderErrorCode enumeration. */ const lastErrorCode = decoderErrorUnreachable /** Options to be used with ::BrotliDecoderSetParameter. */ const ( decoderParamDisableRingBufferReallocation = 0 decoderParamLargeWindow = 1 ) const huffmanTableBits = 8 const huffmanTableMask = 0xFF /* We need the slack region for the following reasons: - doing up to two 16-byte copies for fast backward copying - inserting transformed dictionary word (5 prefix + 24 base + 8 suffix) */ const kRingBufferWriteAheadSlack uint32 = 42 var kCodeLengthCodeOrder = [codeLengthCodes]byte{1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15} /* Static prefix code for the complex code length code lengths. */ var kCodeLengthPrefixLength = [16]byte{2, 2, 2, 3, 2, 2, 2, 4, 2, 2, 2, 3, 2, 2, 2, 4} var kCodeLengthPrefixValue = [16]byte{0, 4, 3, 2, 0, 4, 3, 1, 0, 4, 3, 2, 0, 4, 3, 5} func decoderSetParameter(state *Reader, p int, value uint32) bool { if state.state != stateUninited { return false } switch p { case decoderParamDisableRingBufferReallocation: if !(value == 0) { state.canny_ringbuffer_allocation = 0 } else { state.canny_ringbuffer_allocation = 1 } return true case decoderParamLargeWindow: state.large_window = (!(value == 0)) return true default: return false } } /* Saves error code and converts it to BrotliDecoderResult. */ func saveErrorCode(s *Reader, e int) int { s.error_code = int(e) switch e { case decoderSuccess: return decoderResultSuccess case decoderNeedsMoreInput: return decoderResultNeedsMoreInput case decoderNeedsMoreOutput: return decoderResultNeedsMoreOutput default: return decoderResultError } } /* Decodes WBITS by reading 1 - 7 bits, or 0x11 for "Large Window Brotli". Precondition: bit-reader accumulator has at least 8 bits. */ func decodeWindowBits(s *Reader, br *bitReader) int { var n uint32 var large_window bool = s.large_window s.large_window = false takeBits(br, 1, &n) if n == 0 { s.window_bits = 16 return decoderSuccess } takeBits(br, 3, &n) if n != 0 { s.window_bits = 17 + n return decoderSuccess } takeBits(br, 3, &n) if n == 1 { if large_window { takeBits(br, 1, &n) if n == 1 { return decoderErrorFormatWindowBits } s.large_window = true return decoderSuccess } else { return decoderErrorFormatWindowBits } } if n != 0 { s.window_bits = 8 + n return decoderSuccess } s.window_bits = 17 return decoderSuccess } /* Decodes a number in the range [0..255], by reading 1 - 11 bits. */ func decodeVarLenUint8(s *Reader, br *bitReader, value *uint32) int { var bits uint32 switch s.substate_decode_uint8 { case stateDecodeUint8None: if !safeReadBits(br, 1, &bits) { return decoderNeedsMoreInput } if bits == 0 { *value = 0 return decoderSuccess } fallthrough /* Fall through. */ case stateDecodeUint8Short: if !safeReadBits(br, 3, &bits) { s.substate_decode_uint8 = stateDecodeUint8Short return decoderNeedsMoreInput } if bits == 0 { *value = 1 s.substate_decode_uint8 = stateDecodeUint8None return decoderSuccess } /* Use output value as a temporary storage. It MUST be persisted. */ *value = bits fallthrough /* Fall through. */ case stateDecodeUint8Long: if !safeReadBits(br, *value, &bits) { s.substate_decode_uint8 = stateDecodeUint8Long return decoderNeedsMoreInput } *value = (1 << *value) + bits s.substate_decode_uint8 = stateDecodeUint8None return decoderSuccess default: return decoderErrorUnreachable } } /* Decodes a metablock length and flags by reading 2 - 31 bits. */ func decodeMetaBlockLength(s *Reader, br *bitReader) int { var bits uint32 var i int for { switch s.substate_metablock_header { case stateMetablockHeaderNone: if !safeReadBits(br, 1, &bits) { return decoderNeedsMoreInput } if bits != 0 { s.is_last_metablock = 1 } else { s.is_last_metablock = 0 } s.meta_block_remaining_len = 0 s.is_uncompressed = 0 s.is_metadata = 0 if s.is_last_metablock == 0 { s.substate_metablock_header = stateMetablockHeaderNibbles break } s.substate_metablock_header = stateMetablockHeaderEmpty fallthrough /* Fall through. */ case stateMetablockHeaderEmpty: if !safeReadBits(br, 1, &bits) { return decoderNeedsMoreInput } if bits != 0 { s.substate_metablock_header = stateMetablockHeaderNone return decoderSuccess } s.substate_metablock_header = stateMetablockHeaderNibbles fallthrough /* Fall through. */ case stateMetablockHeaderNibbles: if !safeReadBits(br, 2, &bits) { return decoderNeedsMoreInput } s.size_nibbles = uint(byte(bits + 4)) s.loop_counter = 0 if bits == 3 { s.is_metadata = 1 s.substate_metablock_header = stateMetablockHeaderReserved break } s.substate_metablock_header = stateMetablockHeaderSize fallthrough /* Fall through. */ case stateMetablockHeaderSize: i = s.loop_counter for ; i < int(s.size_nibbles); i++ { if !safeReadBits(br, 4, &bits) { s.loop_counter = i return decoderNeedsMoreInput } if uint(i+1) == s.size_nibbles && s.size_nibbles > 4 && bits == 0 { return decoderErrorFormatExuberantNibble } s.meta_block_remaining_len |= int(bits << uint(i*4)) } s.substate_metablock_header = stateMetablockHeaderUncompressed fallthrough /* Fall through. */ case stateMetablockHeaderUncompressed: if s.is_last_metablock == 0 { if !safeReadBits(br, 1, &bits) { return decoderNeedsMoreInput } if bits != 0 { s.is_uncompressed = 1 } else { s.is_uncompressed = 0 } } s.meta_block_remaining_len++ s.substate_metablock_header = stateMetablockHeaderNone return decoderSuccess case stateMetablockHeaderReserved: if !safeReadBits(br, 1, &bits) { return decoderNeedsMoreInput } if bits != 0 { return decoderErrorFormatReserved } s.substate_metablock_header = stateMetablockHeaderBytes fallthrough /* Fall through. */ case stateMetablockHeaderBytes: if !safeReadBits(br, 2, &bits) { return decoderNeedsMoreInput } if bits == 0 { s.substate_metablock_header = stateMetablockHeaderNone return decoderSuccess } s.size_nibbles = uint(byte(bits)) s.substate_metablock_header = stateMetablockHeaderMetadata fallthrough /* Fall through. */ case stateMetablockHeaderMetadata: i = s.loop_counter for ; i < int(s.size_nibbles); i++ { if !safeReadBits(br, 8, &bits) { s.loop_counter = i return decoderNeedsMoreInput } if uint(i+1) == s.size_nibbles && s.size_nibbles > 1 && bits == 0 { return decoderErrorFormatExuberantMetaNibble } s.meta_block_remaining_len |= int(bits << uint(i*8)) } s.meta_block_remaining_len++ s.substate_metablock_header = stateMetablockHeaderNone return decoderSuccess default: return decoderErrorUnreachable } } } /* Decodes the Huffman code. This method doesn't read data from the bit reader, BUT drops the amount of bits that correspond to the decoded symbol. bits MUST contain at least 15 (BROTLI_HUFFMAN_MAX_CODE_LENGTH) valid bits. */ func decodeSymbol(bits uint32, table []huffmanCode, br *bitReader) uint32 { table = table[bits&huffmanTableMask:] if table[0].bits > huffmanTableBits { var nbits uint32 = uint32(table[0].bits) - huffmanTableBits dropBits(br, huffmanTableBits) table = table[uint32(table[0].value)+((bits>>huffmanTableBits)&bitMask(nbits)):] } dropBits(br, uint32(table[0].bits)) return uint32(table[0].value) } /* Reads and decodes the next Huffman code from bit-stream. This method peeks 16 bits of input and drops 0 - 15 of them. */ func readSymbol(table []huffmanCode, br *bitReader) uint32 { return decodeSymbol(get16BitsUnmasked(br), table, br) } /* Same as DecodeSymbol, but it is known that there is less than 15 bits of input are currently available. */ func safeDecodeSymbol(table []huffmanCode, br *bitReader, result *uint32) bool { var val uint32 var available_bits uint32 = getAvailableBits(br) if available_bits == 0 { if table[0].bits == 0 { *result = uint32(table[0].value) return true } return false /* No valid bits at all. */ } val = uint32(getBitsUnmasked(br)) table = table[val&huffmanTableMask:] if table[0].bits <= huffmanTableBits { if uint32(table[0].bits) <= available_bits { dropBits(br, uint32(table[0].bits)) *result = uint32(table[0].value) return true } else { return false /* Not enough bits for the first level. */ } } if available_bits <= huffmanTableBits { return false /* Not enough bits to move to the second level. */ } /* Speculatively drop HUFFMAN_TABLE_BITS. */ val = (val & bitMask(uint32(table[0].bits))) >> huffmanTableBits available_bits -= huffmanTableBits table = table[uint32(table[0].value)+val:] if available_bits < uint32(table[0].bits) { return false /* Not enough bits for the second level. */ } dropBits(br, huffmanTableBits+uint32(table[0].bits)) *result = uint32(table[0].value) return true } func safeReadSymbol(table []huffmanCode, br *bitReader, result *uint32) bool { var val uint32 if safeGetBits(br, 15, &val) { *result = decodeSymbol(val, table, br) return true } return safeDecodeSymbol(table, br, result) } /* Makes a look-up in first level Huffman table. Peeks 8 bits. */ func preloadSymbol(safe int, table []huffmanCode, br *bitReader, bits *uint32, value *uint32) { if safe != 0 { return } table = table[getBits(br, huffmanTableBits):] *bits = uint32(table[0].bits) *value = uint32(table[0].value) } /* Decodes the next Huffman code using data prepared by PreloadSymbol. Reads 0 - 15 bits. Also peeks 8 following bits. */ func readPreloadedSymbol(table []huffmanCode, br *bitReader, bits *uint32, value *uint32) uint32 { var result uint32 = *value var ext []huffmanCode if *bits > huffmanTableBits { var val uint32 = get16BitsUnmasked(br) ext = table[val&huffmanTableMask:][*value:] var mask uint32 = bitMask((*bits - huffmanTableBits)) dropBits(br, huffmanTableBits) ext = ext[(val>>huffmanTableBits)&mask:] dropBits(br, uint32(ext[0].bits)) result = uint32(ext[0].value) } else { dropBits(br, *bits) } preloadSymbol(0, table, br, bits, value) return result } func log2Floor(x uint32) uint32 { var result uint32 = 0 for x != 0 { x >>= 1 result++ } return result } /* Reads (s->symbol + 1) symbols. Totally 1..4 symbols are read, 1..11 bits each. The list of symbols MUST NOT contain duplicates. */ func readSimpleHuffmanSymbols(alphabet_size uint32, max_symbol uint32, s *Reader) int { var br *bitReader = &s.br var max_bits uint32 = log2Floor(alphabet_size - 1) var i uint32 = s.sub_loop_counter /* max_bits == 1..11; symbol == 0..3; 1..44 bits will be read. */ var num_symbols uint32 = s.symbol for i <= num_symbols { var v uint32 if !safeReadBits(br, max_bits, &v) { s.sub_loop_counter = i s.substate_huffman = stateHuffmanSimpleRead return decoderNeedsMoreInput } if v >= max_symbol { return decoderErrorFormatSimpleHuffmanAlphabet } s.symbols_lists_array[i] = uint16(v) i++ } for i = 0; i < num_symbols; i++ { var k uint32 = i + 1 for ; k <= num_symbols; k++ { if s.symbols_lists_array[i] == s.symbols_lists_array[k] { return decoderErrorFormatSimpleHuffmanSame } } } return decoderSuccess } /* Process single decoded symbol code length: A) reset the repeat variable B) remember code length (if it is not 0) C) extend corresponding index-chain D) reduce the Huffman space E) update the histogram */ func processSingleCodeLength(code_len uint32, symbol *uint32, repeat *uint32, space *uint32, prev_code_len *uint32, symbol_lists symbolList, code_length_histo []uint16, next_symbol []int) { *repeat = 0 if code_len != 0 { /* code_len == 1..15 */ symbolListPut(symbol_lists, next_symbol[code_len], uint16(*symbol)) next_symbol[code_len] = int(*symbol) *prev_code_len = code_len *space -= 32768 >> code_len code_length_histo[code_len]++ } (*symbol)++ } /* Process repeated symbol code length. A) Check if it is the extension of previous repeat sequence; if the decoded value is not BROTLI_REPEAT_PREVIOUS_CODE_LENGTH, then it is a new symbol-skip B) Update repeat variable C) Check if operation is feasible (fits alphabet) D) For each symbol do the same operations as in ProcessSingleCodeLength PRECONDITION: code_len == BROTLI_REPEAT_PREVIOUS_CODE_LENGTH or code_len == BROTLI_REPEAT_ZERO_CODE_LENGTH */ func processRepeatedCodeLength(code_len uint32, repeat_delta uint32, alphabet_size uint32, symbol *uint32, repeat *uint32, space *uint32, prev_code_len *uint32, repeat_code_len *uint32, symbol_lists symbolList, code_length_histo []uint16, next_symbol []int) { var old_repeat uint32 /* for BROTLI_REPEAT_ZERO_CODE_LENGTH */ /* for BROTLI_REPEAT_ZERO_CODE_LENGTH */ var extra_bits uint32 = 3 var new_len uint32 = 0 if code_len == repeatPreviousCodeLength { new_len = *prev_code_len extra_bits = 2 } if *repeat_code_len != new_len { *repeat = 0 *repeat_code_len = new_len } old_repeat = *repeat if *repeat > 0 { *repeat -= 2 *repeat <<= extra_bits } *repeat += repeat_delta + 3 repeat_delta = *repeat - old_repeat if *symbol+repeat_delta > alphabet_size { *symbol = alphabet_size *space = 0xFFFFF return } if *repeat_code_len != 0 { var last uint = uint(*symbol + repeat_delta) var next int = next_symbol[*repeat_code_len] for { symbolListPut(symbol_lists, next, uint16(*symbol)) next = int(*symbol) (*symbol)++ if (*symbol) == uint32(last) { break } } next_symbol[*repeat_code_len] = next *space -= repeat_delta << (15 - *repeat_code_len) code_length_histo[*repeat_code_len] = uint16(uint32(code_length_histo[*repeat_code_len]) + repeat_delta) } else { *symbol += repeat_delta } } /* Reads and decodes symbol codelengths. */ func readSymbolCodeLengths(alphabet_size uint32, s *Reader) int { var br *bitReader = &s.br var symbol uint32 = s.symbol var repeat uint32 = s.repeat var space uint32 = s.space var prev_code_len uint32 = s.prev_code_len var repeat_code_len uint32 = s.repeat_code_len var symbol_lists symbolList = s.symbol_lists var code_length_histo []uint16 = s.code_length_histo[:] var next_symbol []int = s.next_symbol[:] if !warmupBitReader(br) { return decoderNeedsMoreInput } var p []huffmanCode for symbol < alphabet_size && space > 0 { p = s.table[:] var code_len uint32 if !checkInputAmount(br, shortFillBitWindowRead) { s.symbol = symbol s.repeat = repeat s.prev_code_len = prev_code_len s.repeat_code_len = repeat_code_len s.space = space return decoderNeedsMoreInput } fillBitWindow16(br) p = p[getBitsUnmasked(br)&uint64(bitMask(huffmanMaxCodeLengthCodeLength)):] dropBits(br, uint32(p[0].bits)) /* Use 1..5 bits. */ code_len = uint32(p[0].value) /* code_len == 0..17 */ if code_len < repeatPreviousCodeLength { processSingleCodeLength(code_len, &symbol, &repeat, &space, &prev_code_len, symbol_lists, code_length_histo, next_symbol) /* code_len == 16..17, extra_bits == 2..3 */ } else { var extra_bits uint32 if code_len == repeatPreviousCodeLength { extra_bits = 2 } else { extra_bits = 3 } var repeat_delta uint32 = uint32(getBitsUnmasked(br)) & bitMask(extra_bits) dropBits(br, extra_bits) processRepeatedCodeLength(code_len, repeat_delta, alphabet_size, &symbol, &repeat, &space, &prev_code_len, &repeat_code_len, symbol_lists, code_length_histo, next_symbol) } } s.space = space return decoderSuccess } func safeReadSymbolCodeLengths(alphabet_size uint32, s *Reader) int { var br *bitReader = &s.br var get_byte bool = false var p []huffmanCode for s.symbol < alphabet_size && s.space > 0 { p = s.table[:] var code_len uint32 var available_bits uint32 var bits uint32 = 0 if get_byte && !pullByte(br) { return decoderNeedsMoreInput } get_byte = false available_bits = getAvailableBits(br) if available_bits != 0 { bits = uint32(getBitsUnmasked(br)) } p = p[bits&bitMask(huffmanMaxCodeLengthCodeLength):] if uint32(p[0].bits) > available_bits { get_byte = true continue } code_len = uint32(p[0].value) /* code_len == 0..17 */ if code_len < repeatPreviousCodeLength { dropBits(br, uint32(p[0].bits)) processSingleCodeLength(code_len, &s.symbol, &s.repeat, &s.space, &s.prev_code_len, s.symbol_lists, s.code_length_histo[:], s.next_symbol[:]) /* code_len == 16..17, extra_bits == 2..3 */ } else { var extra_bits uint32 = code_len - 14 var repeat_delta uint32 = (bits >> p[0].bits) & bitMask(extra_bits) if available_bits < uint32(p[0].bits)+extra_bits { get_byte = true continue } dropBits(br, uint32(p[0].bits)+extra_bits) processRepeatedCodeLength(code_len, repeat_delta, alphabet_size, &s.symbol, &s.repeat, &s.space, &s.prev_code_len, &s.repeat_code_len, s.symbol_lists, s.code_length_histo[:], s.next_symbol[:]) } } return decoderSuccess } /* Reads and decodes 15..18 codes using static prefix code. Each code is 2..4 bits long. In total 30..72 bits are used. */ func readCodeLengthCodeLengths(s *Reader) int { var br *bitReader = &s.br var num_codes uint32 = s.repeat var space uint32 = s.space var i uint32 = s.sub_loop_counter for ; i < codeLengthCodes; i++ { var code_len_idx byte = kCodeLengthCodeOrder[i] var ix uint32 var v uint32 if !safeGetBits(br, 4, &ix) { var available_bits uint32 = getAvailableBits(br) if available_bits != 0 { ix = uint32(getBitsUnmasked(br) & 0xF) } else { ix = 0 } if uint32(kCodeLengthPrefixLength[ix]) > available_bits { s.sub_loop_counter = i s.repeat = num_codes s.space = space s.substate_huffman = stateHuffmanComplex return decoderNeedsMoreInput } } v = uint32(kCodeLengthPrefixValue[ix]) dropBits(br, uint32(kCodeLengthPrefixLength[ix])) s.code_length_code_lengths[code_len_idx] = byte(v) if v != 0 { space = space - (32 >> v) num_codes++ s.code_length_histo[v]++ if space-1 >= 32 { /* space is 0 or wrapped around. */ break } } } if num_codes != 1 && space != 0 { return decoderErrorFormatClSpace } return decoderSuccess } /* Decodes the Huffman tables. There are 2 scenarios: A) Huffman code contains only few symbols (1..4). Those symbols are read directly; their code lengths are defined by the number of symbols. For this scenario 4 - 49 bits will be read. B) 2-phase decoding: B.1) Small Huffman table is decoded; it is specified with code lengths encoded with predefined entropy code. 32 - 74 bits are used. B.2) Decoded table is used to decode code lengths of symbols in resulting Huffman table. In worst case 3520 bits are read. */ func readHuffmanCode(alphabet_size uint32, max_symbol uint32, table []huffmanCode, opt_table_size *uint32, s *Reader) int { var br *bitReader = &s.br /* Unnecessary masking, but might be good for safety. */ alphabet_size &= 0x7FF /* State machine. */ for { switch s.substate_huffman { case stateHuffmanNone: if !safeReadBits(br, 2, &s.sub_loop_counter) { return decoderNeedsMoreInput } /* The value is used as follows: 1 for simple code; 0 for no skipping, 2 skips 2 code lengths, 3 skips 3 code lengths */ if s.sub_loop_counter != 1 { s.space = 32 s.repeat = 0 /* num_codes */ var i int for i = 0; i <= huffmanMaxCodeLengthCodeLength; i++ { s.code_length_histo[i] = 0 } for i = 0; i < codeLengthCodes; i++ { s.code_length_code_lengths[i] = 0 } s.substate_huffman = stateHuffmanComplex continue } fallthrough /* Read symbols, codes & code lengths directly. */ case stateHuffmanSimpleSize: if !safeReadBits(br, 2, &s.symbol) { /* num_symbols */ s.substate_huffman = stateHuffmanSimpleSize return decoderNeedsMoreInput } s.sub_loop_counter = 0 fallthrough case stateHuffmanSimpleRead: { var result int = readSimpleHuffmanSymbols(alphabet_size, max_symbol, s) if result != decoderSuccess { return result } } fallthrough case stateHuffmanSimpleBuild: var table_size uint32 if s.symbol == 3 { var bits uint32 if !safeReadBits(br, 1, &bits) { s.substate_huffman = stateHuffmanSimpleBuild return decoderNeedsMoreInput } s.symbol += bits } table_size = buildSimpleHuffmanTable(table, huffmanTableBits, s.symbols_lists_array[:], s.symbol) if opt_table_size != nil { *opt_table_size = table_size } s.substate_huffman = stateHuffmanNone return decoderSuccess /* Decode Huffman-coded code lengths. */ case stateHuffmanComplex: { var i uint32 var result int = readCodeLengthCodeLengths(s) if result != decoderSuccess { return result } buildCodeLengthsHuffmanTable(s.table[:], s.code_length_code_lengths[:], s.code_length_histo[:]) for i = 0; i < 16; i++ { s.code_length_histo[i] = 0 } for i = 0; i <= huffmanMaxCodeLength; i++ { s.next_symbol[i] = int(i) - (huffmanMaxCodeLength + 1) symbolListPut(s.symbol_lists, s.next_symbol[i], 0xFFFF) } s.symbol = 0 s.prev_code_len = initialRepeatedCodeLength s.repeat = 0 s.repeat_code_len = 0 s.space = 32768 s.substate_huffman = stateHuffmanLengthSymbols } fallthrough case stateHuffmanLengthSymbols: var table_size uint32 var result int = readSymbolCodeLengths(max_symbol, s) if result == decoderNeedsMoreInput { result = safeReadSymbolCodeLengths(max_symbol, s) } if result != decoderSuccess { return result } if s.space != 0 { return decoderErrorFormatHuffmanSpace } table_size = buildHuffmanTable(table, huffmanTableBits, s.symbol_lists, s.code_length_histo[:]) if opt_table_size != nil { *opt_table_size = table_size } s.substate_huffman = stateHuffmanNone return decoderSuccess default: return decoderErrorUnreachable } } } /* Decodes a block length by reading 3..39 bits. */ func readBlockLength(table []huffmanCode, br *bitReader) uint32 { var code uint32 var nbits uint32 code = readSymbol(table, br) nbits = kBlockLengthPrefixCode[code].nbits /* nbits == 2..24 */ return kBlockLengthPrefixCode[code].offset + readBits(br, nbits) } /* WARNING: if state is not BROTLI_STATE_READ_BLOCK_LENGTH_NONE, then reading can't be continued with ReadBlockLength. */ func safeReadBlockLength(s *Reader, result *uint32, table []huffmanCode, br *bitReader) bool { var index uint32 if s.substate_read_block_length == stateReadBlockLengthNone { if !safeReadSymbol(table, br, &index) { return false } } else { index = s.block_length_index } { var bits uint32 /* nbits == 2..24 */ var nbits uint32 = kBlockLengthPrefixCode[index].nbits if !safeReadBits(br, nbits, &bits) { s.block_length_index = index s.substate_read_block_length = stateReadBlockLengthSuffix return false } *result = kBlockLengthPrefixCode[index].offset + bits s.substate_read_block_length = stateReadBlockLengthNone return true } } /* Transform: 1) initialize list L with values 0, 1,... 255 2) For each input element X: 2.1) let Y = L[X] 2.2) remove X-th element from L 2.3) prepend Y to L 2.4) append Y to output In most cases max(Y) <= 7, so most of L remains intact. To reduce the cost of initialization, we reuse L, remember the upper bound of Y values, and reinitialize only first elements in L. Most of input values are 0 and 1. To reduce number of branches, we replace inner for loop with do-while. */ func inverseMoveToFrontTransform(v []byte, v_len uint32, state *Reader) { var mtf [256]byte var i int for i = 1; i < 256; i++ { mtf[i] = byte(i) } var mtf_1 byte /* Transform the input. */ for i = 0; uint32(i) < v_len; i++ { var index int = int(v[i]) var value byte = mtf[index] v[i] = value mtf_1 = value for index >= 1 { index-- mtf[index+1] = mtf[index] } mtf[0] = mtf_1 } } /* Decodes a series of Huffman table using ReadHuffmanCode function. */ func huffmanTreeGroupDecode(group *huffmanTreeGroup, s *Reader) int { if s.substate_tree_group != stateTreeGroupLoop { s.next = group.codes s.htree_index = 0 s.substate_tree_group = stateTreeGroupLoop } for s.htree_index < int(group.num_htrees) { var table_size uint32 var result int = readHuffmanCode(uint32(group.alphabet_size), uint32(group.max_symbol), s.next, &table_size, s) if result != decoderSuccess { return result } group.htrees[s.htree_index] = s.next s.next = s.next[table_size:] s.htree_index++ } s.substate_tree_group = stateTreeGroupNone return decoderSuccess } /* Decodes a context map. Decoding is done in 4 phases: 1) Read auxiliary information (6..16 bits) and allocate memory. In case of trivial context map, decoding is finished at this phase. 2) Decode Huffman table using ReadHuffmanCode function. This table will be used for reading context map items. 3) Read context map items; "0" values could be run-length encoded. 4) Optionally, apply InverseMoveToFront transform to the resulting map. */ func decodeContextMap(context_map_size uint32, num_htrees *uint32, context_map_arg *[]byte, s *Reader) int { var br *bitReader = &s.br var result int = decoderSuccess switch int(s.substate_context_map) { case stateContextMapNone: result = decodeVarLenUint8(s, br, num_htrees) if result != decoderSuccess { return result } (*num_htrees)++ s.context_index = 0 *context_map_arg = make([]byte, uint(context_map_size)) if *context_map_arg == nil { return decoderErrorAllocContextMap } if *num_htrees <= 1 { for i := 0; i < int(context_map_size); i++ { (*context_map_arg)[i] = 0 } return decoderSuccess } s.substate_context_map = stateContextMapReadPrefix fallthrough /* Fall through. */ case stateContextMapReadPrefix: { var bits uint32 /* In next stage ReadHuffmanCode uses at least 4 bits, so it is safe to peek 4 bits ahead. */ if !safeGetBits(br, 5, &bits) { return decoderNeedsMoreInput } if bits&1 != 0 { /* Use RLE for zeros. */ s.max_run_length_prefix = (bits >> 1) + 1 dropBits(br, 5) } else { s.max_run_length_prefix = 0 dropBits(br, 1) } s.substate_context_map = stateContextMapHuffman } fallthrough /* Fall through. */ case stateContextMapHuffman: { var alphabet_size uint32 = *num_htrees + s.max_run_length_prefix result = readHuffmanCode(alphabet_size, alphabet_size, s.context_map_table[:], nil, s) if result != decoderSuccess { return result } s.code = 0xFFFF s.substate_context_map = stateContextMapDecode } fallthrough /* Fall through. */ case stateContextMapDecode: { var context_index uint32 = s.context_index var max_run_length_prefix uint32 = s.max_run_length_prefix var context_map []byte = *context_map_arg var code uint32 = s.code var skip_preamble bool = (code != 0xFFFF) for context_index < context_map_size || skip_preamble { if !skip_preamble { if !safeReadSymbol(s.context_map_table[:], br, &code) { s.code = 0xFFFF s.context_index = context_index return decoderNeedsMoreInput } if code == 0 { context_map[context_index] = 0 context_index++ continue } if code > max_run_length_prefix { context_map[context_index] = byte(code - max_run_length_prefix) context_index++ continue } } else { skip_preamble = false } /* RLE sub-stage. */ { var reps uint32 if !safeReadBits(br, code, &reps) { s.code = code s.context_index = context_index return decoderNeedsMoreInput } reps += 1 << code if context_index+reps > context_map_size { return decoderErrorFormatContextMapRepeat } for { context_map[context_index] = 0 context_index++ reps-- if reps == 0 { break } } } } } fallthrough case stateContextMapTransform: var bits uint32 if !safeReadBits(br, 1, &bits) { s.substate_context_map = stateContextMapTransform return decoderNeedsMoreInput } if bits != 0 { inverseMoveToFrontTransform(*context_map_arg, context_map_size, s) } s.substate_context_map = stateContextMapNone return decoderSuccess default: return decoderErrorUnreachable } } /* Decodes a command or literal and updates block type ring-buffer. Reads 3..54 bits. */ func decodeBlockTypeAndLength(safe int, s *Reader, tree_type int) bool { var max_block_type uint32 = s.num_block_types[tree_type] var type_tree []huffmanCode type_tree = s.block_type_trees[tree_type*huffmanMaxSize258:] var len_tree []huffmanCode len_tree = s.block_len_trees[tree_type*huffmanMaxSize26:] var br *bitReader = &s.br var ringbuffer []uint32 = s.block_type_rb[tree_type*2:] var block_type uint32 if max_block_type <= 1 { return false } /* Read 0..15 + 3..39 bits. */ if safe == 0 { block_type = readSymbol(type_tree, br) s.block_length[tree_type] = readBlockLength(len_tree, br) } else { var memento bitReaderState bitReaderSaveState(br, &memento) if !safeReadSymbol(type_tree, br, &block_type) { return false } if !safeReadBlockLength(s, &s.block_length[tree_type], len_tree, br) { s.substate_read_block_length = stateReadBlockLengthNone bitReaderRestoreState(br, &memento) return false } } if block_type == 1 { block_type = ringbuffer[1] + 1 } else if block_type == 0 { block_type = ringbuffer[0] } else { block_type -= 2 } if block_type >= max_block_type { block_type -= max_block_type } ringbuffer[0] = ringbuffer[1] ringbuffer[1] = block_type return true } func detectTrivialLiteralBlockTypes(s *Reader) { var i uint for i = 0; i < 8; i++ { s.trivial_literal_contexts[i] = 0 } for i = 0; uint32(i) < s.num_block_types[0]; i++ { var offset uint = i << literalContextBits var error uint = 0 var sample uint = uint(s.context_map[offset]) var j uint for j = 0; j < 1<>5] |= 1 << (i & 31) } } } func prepareLiteralDecoding(s *Reader) { var context_mode byte var trivial uint var block_type uint32 = s.block_type_rb[1] var context_offset uint32 = block_type << literalContextBits s.context_map_slice = s.context_map[context_offset:] trivial = uint(s.trivial_literal_contexts[block_type>>5]) s.trivial_literal_context = int((trivial >> (block_type & 31)) & 1) s.literal_htree = []huffmanCode(s.literal_hgroup.htrees[s.context_map_slice[0]]) context_mode = s.context_modes[block_type] & 3 s.context_lookup = getContextLUT(int(context_mode)) } /* Decodes the block type and updates the state for literal context. Reads 3..54 bits. */ func decodeLiteralBlockSwitchInternal(safe int, s *Reader) bool { if !decodeBlockTypeAndLength(safe, s, 0) { return false } prepareLiteralDecoding(s) return true } func decodeLiteralBlockSwitch(s *Reader) { decodeLiteralBlockSwitchInternal(0, s) } func safeDecodeLiteralBlockSwitch(s *Reader) bool { return decodeLiteralBlockSwitchInternal(1, s) } /* Block switch for insert/copy length. Reads 3..54 bits. */ func decodeCommandBlockSwitchInternal(safe int, s *Reader) bool { if !decodeBlockTypeAndLength(safe, s, 1) { return false } s.htree_command = []huffmanCode(s.insert_copy_hgroup.htrees[s.block_type_rb[3]]) return true } func decodeCommandBlockSwitch(s *Reader) { decodeCommandBlockSwitchInternal(0, s) } func safeDecodeCommandBlockSwitch(s *Reader) bool { return decodeCommandBlockSwitchInternal(1, s) } /* Block switch for distance codes. Reads 3..54 bits. */ func decodeDistanceBlockSwitchInternal(safe int, s *Reader) bool { if !decodeBlockTypeAndLength(safe, s, 2) { return false } s.dist_context_map_slice = s.dist_context_map[s.block_type_rb[5]< s.ringbuffer_size { pos = uint(s.ringbuffer_size) } else { pos = uint(s.pos) } var partial_pos_rb uint = (s.rb_roundtrips * uint(s.ringbuffer_size)) + pos return partial_pos_rb - s.partial_pos_out } /* Dumps output. Returns BROTLI_DECODER_NEEDS_MORE_OUTPUT only if there is more output to push and either ring-buffer is as big as window size, or |force| is true. */ func writeRingBuffer(s *Reader, available_out *uint, next_out *[]byte, total_out *uint, force bool) int { var start []byte start = s.ringbuffer[s.partial_pos_out&uint(s.ringbuffer_mask):] var to_write uint = unwrittenBytes(s, true) var num_written uint = *available_out if num_written > to_write { num_written = to_write } if s.meta_block_remaining_len < 0 { return decoderErrorFormatBlockLength1 } if next_out != nil && *next_out == nil { *next_out = start } else { if next_out != nil { copy(*next_out, start[:num_written]) *next_out = (*next_out)[num_written:] } } *available_out -= num_written s.partial_pos_out += num_written if total_out != nil { *total_out = s.partial_pos_out } if num_written < to_write { if s.ringbuffer_size == 1<= s.ringbuffer_size { s.pos -= s.ringbuffer_size s.rb_roundtrips++ if uint(s.pos) != 0 { s.should_wrap_ringbuffer = 1 } else { s.should_wrap_ringbuffer = 0 } } return decoderSuccess } func wrapRingBuffer(s *Reader) { if s.should_wrap_ringbuffer != 0 { copy(s.ringbuffer, s.ringbuffer_end[:uint(s.pos)]) s.should_wrap_ringbuffer = 0 } } /* Allocates ring-buffer. s->ringbuffer_size MUST be updated by BrotliCalculateRingBufferSize before this function is called. Last two bytes of ring-buffer are initialized to 0, so context calculation could be done uniformly for the first two and all other positions. */ func ensureRingBuffer(s *Reader) bool { var old_ringbuffer []byte = s.ringbuffer if s.ringbuffer_size == s.new_ringbuffer_size { return true } s.ringbuffer = make([]byte, uint(s.new_ringbuffer_size)+uint(kRingBufferWriteAheadSlack)) if s.ringbuffer == nil { /* Restore previous value. */ s.ringbuffer = old_ringbuffer return false } s.ringbuffer[s.new_ringbuffer_size-2] = 0 s.ringbuffer[s.new_ringbuffer_size-1] = 0 if !(old_ringbuffer == nil) { copy(s.ringbuffer, old_ringbuffer[:uint(s.pos)]) old_ringbuffer = nil } s.ringbuffer_size = s.new_ringbuffer_size s.ringbuffer_mask = s.new_ringbuffer_size - 1 s.ringbuffer_end = s.ringbuffer[s.ringbuffer_size:] return true } func copyUncompressedBlockToOutput(available_out *uint, next_out *[]byte, total_out *uint, s *Reader) int { /* TODO: avoid allocation for single uncompressed block. */ if !ensureRingBuffer(s) { return decoderErrorAllocRingBuffer1 } /* State machine */ for { switch s.substate_uncompressed { case stateUncompressedNone: { var nbytes int = int(getRemainingBytes(&s.br)) if nbytes > s.meta_block_remaining_len { nbytes = s.meta_block_remaining_len } if s.pos+nbytes > s.ringbuffer_size { nbytes = s.ringbuffer_size - s.pos } /* Copy remaining bytes from s->br.buf_ to ring-buffer. */ copyBytes(s.ringbuffer[s.pos:], &s.br, uint(nbytes)) s.pos += nbytes s.meta_block_remaining_len -= nbytes if s.pos < 1<>1 >= min_size { new_ringbuffer_size >>= 1 } } s.new_ringbuffer_size = new_ringbuffer_size } /* Reads 1..256 2-bit context modes. */ func readContextModes(s *Reader) int { var br *bitReader = &s.br var i int = s.loop_counter for i < int(s.num_block_types[0]) { var bits uint32 if !safeReadBits(br, 2, &bits) { s.loop_counter = i return decoderNeedsMoreInput } s.context_modes[i] = byte(bits) i++ } return decoderSuccess } func takeDistanceFromRingBuffer(s *Reader) { if s.distance_code == 0 { s.dist_rb_idx-- s.distance_code = s.dist_rb[s.dist_rb_idx&3] /* Compensate double distance-ring-buffer roll for dictionary items. */ s.distance_context = 1 } else { var distance_code int = s.distance_code << 1 const kDistanceShortCodeIndexOffset uint32 = 0xAAAFFF1B const kDistanceShortCodeValueOffset uint32 = 0xFA5FA500 var v int = (s.dist_rb_idx + int(kDistanceShortCodeIndexOffset>>uint(distance_code))) & 0x3 /* kDistanceShortCodeIndexOffset has 2-bit values from LSB: 3, 2, 1, 0, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2 */ /* kDistanceShortCodeValueOffset has 2-bit values from LSB: -0, 0,-0, 0,-1, 1,-2, 2,-3, 3,-1, 1,-2, 2,-3, 3 */ s.distance_code = s.dist_rb[v] v = int(kDistanceShortCodeValueOffset>>uint(distance_code)) & 0x3 if distance_code&0x3 != 0 { s.distance_code += v } else { s.distance_code -= v if s.distance_code <= 0 { /* A huge distance will cause a () soon. This is a little faster than failing here. */ s.distance_code = 0x7FFFFFFF } } } } func safeReadBitsMaybeZero(br *bitReader, n_bits uint32, val *uint32) bool { if n_bits != 0 { return safeReadBits(br, n_bits, val) } else { *val = 0 return true } } /* Precondition: s->distance_code < 0. */ func readDistanceInternal(safe int, s *Reader, br *bitReader) bool { var distval int var memento bitReaderState var distance_tree []huffmanCode = []huffmanCode(s.distance_hgroup.htrees[s.dist_htree_index]) if safe == 0 { s.distance_code = int(readSymbol(distance_tree, br)) } else { var code uint32 bitReaderSaveState(br, &memento) if !safeReadSymbol(distance_tree, br, &code) { return false } s.distance_code = int(code) } /* Convert the distance code to the actual distance by possibly looking up past distances from the s->ringbuffer. */ s.distance_context = 0 if s.distance_code&^0xF == 0 { takeDistanceFromRingBuffer(s) s.block_length[2]-- return true } distval = s.distance_code - int(s.num_direct_distance_codes) if distval >= 0 { var nbits uint32 var postfix int var offset int if safe == 0 && (s.distance_postfix_bits == 0) { nbits = (uint32(distval) >> 1) + 1 offset = ((2 + (distval & 1)) << nbits) - 4 s.distance_code = int(s.num_direct_distance_codes) + offset + int(readBits(br, nbits)) } else { /* This branch also works well when s->distance_postfix_bits == 0. */ var bits uint32 postfix = distval & s.distance_postfix_mask distval >>= s.distance_postfix_bits nbits = (uint32(distval) >> 1) + 1 if safe != 0 { if !safeReadBitsMaybeZero(br, nbits, &bits) { s.distance_code = -1 /* Restore precondition. */ bitReaderRestoreState(br, &memento) return false } } else { bits = readBits(br, nbits) } offset = ((2 + (distval & 1)) << nbits) - 4 s.distance_code = int(s.num_direct_distance_codes) + ((offset + int(bits)) << s.distance_postfix_bits) + postfix } } s.distance_code = s.distance_code - numDistanceShortCodes + 1 s.block_length[2]-- return true } func readDistance(s *Reader, br *bitReader) { readDistanceInternal(0, s, br) } func safeReadDistance(s *Reader, br *bitReader) bool { return readDistanceInternal(1, s, br) } func readCommandInternal(safe int, s *Reader, br *bitReader, insert_length *int) bool { var cmd_code uint32 var insert_len_extra uint32 = 0 var copy_length uint32 var v cmdLutElement var memento bitReaderState if safe == 0 { cmd_code = readSymbol(s.htree_command, br) } else { bitReaderSaveState(br, &memento) if !safeReadSymbol(s.htree_command, br, &cmd_code) { return false } } v = kCmdLut[cmd_code] s.distance_code = int(v.distance_code) s.distance_context = int(v.context) s.dist_htree_index = s.dist_context_map_slice[s.distance_context] *insert_length = int(v.insert_len_offset) if safe == 0 { if v.insert_len_extra_bits != 0 { insert_len_extra = readBits(br, uint32(v.insert_len_extra_bits)) } copy_length = readBits(br, uint32(v.copy_len_extra_bits)) } else { if !safeReadBitsMaybeZero(br, uint32(v.insert_len_extra_bits), &insert_len_extra) || !safeReadBitsMaybeZero(br, uint32(v.copy_len_extra_bits), ©_length) { bitReaderRestoreState(br, &memento) return false } } s.copy_length = int(copy_length) + int(v.copy_len_offset) s.block_length[1]-- *insert_length += int(insert_len_extra) return true } func readCommand(s *Reader, br *bitReader, insert_length *int) { readCommandInternal(0, s, br, insert_length) } func safeReadCommand(s *Reader, br *bitReader, insert_length *int) bool { return readCommandInternal(1, s, br, insert_length) } func checkInputAmountMaybeSafe(safe int, br *bitReader, num uint) bool { if safe != 0 { return true } return checkInputAmount(br, num) } func processCommandsInternal(safe int, s *Reader) int { var pos int = s.pos var i int = s.loop_counter var result int = decoderSuccess var br *bitReader = &s.br var hc []huffmanCode if !checkInputAmountMaybeSafe(safe, br, 28) { result = decoderNeedsMoreInput goto saveStateAndReturn } if safe == 0 { warmupBitReader(br) } /* Jump into state machine. */ if s.state == stateCommandBegin { goto CommandBegin } else if s.state == stateCommandInner { goto CommandInner } else if s.state == stateCommandPostDecodeLiterals { goto CommandPostDecodeLiterals } else if s.state == stateCommandPostWrapCopy { goto CommandPostWrapCopy } else { return decoderErrorUnreachable } CommandBegin: if safe != 0 { s.state = stateCommandBegin } if !checkInputAmountMaybeSafe(safe, br, 28) { /* 156 bits + 7 bytes */ s.state = stateCommandBegin result = decoderNeedsMoreInput goto saveStateAndReturn } if s.block_length[1] == 0 { if safe != 0 { if !safeDecodeCommandBlockSwitch(s) { result = decoderNeedsMoreInput goto saveStateAndReturn } } else { decodeCommandBlockSwitch(s) } goto CommandBegin } /* Read the insert/copy length in the command. */ if safe != 0 { if !safeReadCommand(s, br, &i) { result = decoderNeedsMoreInput goto saveStateAndReturn } } else { readCommand(s, br, &i) } if i == 0 { goto CommandPostDecodeLiterals } s.meta_block_remaining_len -= i CommandInner: if safe != 0 { s.state = stateCommandInner } /* Read the literals in the command. */ if s.trivial_literal_context != 0 { var bits uint32 var value uint32 preloadSymbol(safe, s.literal_htree, br, &bits, &value) for { if !checkInputAmountMaybeSafe(safe, br, 28) { /* 162 bits + 7 bytes */ s.state = stateCommandInner result = decoderNeedsMoreInput goto saveStateAndReturn } if s.block_length[0] == 0 { if safe != 0 { if !safeDecodeLiteralBlockSwitch(s) { result = decoderNeedsMoreInput goto saveStateAndReturn } } else { decodeLiteralBlockSwitch(s) } preloadSymbol(safe, s.literal_htree, br, &bits, &value) if s.trivial_literal_context == 0 { goto CommandInner } } if safe == 0 { s.ringbuffer[pos] = byte(readPreloadedSymbol(s.literal_htree, br, &bits, &value)) } else { var literal uint32 if !safeReadSymbol(s.literal_htree, br, &literal) { result = decoderNeedsMoreInput goto saveStateAndReturn } s.ringbuffer[pos] = byte(literal) } s.block_length[0]-- pos++ if pos == s.ringbuffer_size { s.state = stateCommandInnerWrite i-- goto saveStateAndReturn } i-- if i == 0 { break } } } else { var p1 byte = s.ringbuffer[(pos-1)&s.ringbuffer_mask] var p2 byte = s.ringbuffer[(pos-2)&s.ringbuffer_mask] for { var context byte if !checkInputAmountMaybeSafe(safe, br, 28) { /* 162 bits + 7 bytes */ s.state = stateCommandInner result = decoderNeedsMoreInput goto saveStateAndReturn } if s.block_length[0] == 0 { if safe != 0 { if !safeDecodeLiteralBlockSwitch(s) { result = decoderNeedsMoreInput goto saveStateAndReturn } } else { decodeLiteralBlockSwitch(s) } if s.trivial_literal_context != 0 { goto CommandInner } } context = getContext(p1, p2, s.context_lookup) hc = []huffmanCode(s.literal_hgroup.htrees[s.context_map_slice[context]]) p2 = p1 if safe == 0 { p1 = byte(readSymbol(hc, br)) } else { var literal uint32 if !safeReadSymbol(hc, br, &literal) { result = decoderNeedsMoreInput goto saveStateAndReturn } p1 = byte(literal) } s.ringbuffer[pos] = p1 s.block_length[0]-- pos++ if pos == s.ringbuffer_size { s.state = stateCommandInnerWrite i-- goto saveStateAndReturn } i-- if i == 0 { break } } } if s.meta_block_remaining_len <= 0 { s.state = stateMetablockDone goto saveStateAndReturn } CommandPostDecodeLiterals: if safe != 0 { s.state = stateCommandPostDecodeLiterals } if s.distance_code >= 0 { /* Implicit distance case. */ if s.distance_code != 0 { s.distance_context = 0 } else { s.distance_context = 1 } s.dist_rb_idx-- s.distance_code = s.dist_rb[s.dist_rb_idx&3] } else { /* Read distance code in the command, unless it was implicitly zero. */ if s.block_length[2] == 0 { if safe != 0 { if !safeDecodeDistanceBlockSwitch(s) { result = decoderNeedsMoreInput goto saveStateAndReturn } } else { decodeDistanceBlockSwitch(s) } } if safe != 0 { if !safeReadDistance(s, br) { result = decoderNeedsMoreInput goto saveStateAndReturn } } else { readDistance(s, br) } } if s.max_distance != s.max_backward_distance { if pos < s.max_backward_distance { s.max_distance = pos } else { s.max_distance = s.max_backward_distance } } i = s.copy_length /* Apply copy of LZ77 back-reference, or static dictionary reference if the distance is larger than the max LZ77 distance */ if s.distance_code > s.max_distance { /* The maximum allowed distance is BROTLI_MAX_ALLOWED_DISTANCE = 0x7FFFFFFC. With this choice, no signed overflow can occur after decoding a special distance code (e.g., after adding 3 to the last distance). */ if s.distance_code > maxAllowedDistance { return decoderErrorFormatDistance } if i >= minDictionaryWordLength && i <= maxDictionaryWordLength { var address int = s.distance_code - s.max_distance - 1 var words *dictionary = s.dictionary var trans *transforms = s.transforms var offset int = int(s.dictionary.offsets_by_length[i]) var shift uint32 = uint32(s.dictionary.size_bits_by_length[i]) var mask int = int(bitMask(shift)) var word_idx int = address & mask var transform_idx int = address >> shift /* Compensate double distance-ring-buffer roll. */ s.dist_rb_idx += s.distance_context offset += word_idx * i if words.data == nil { return decoderErrorDictionaryNotSet } if transform_idx < int(trans.num_transforms) { var word []byte word = words.data[offset:] var len int = i if transform_idx == int(trans.cutOffTransforms[0]) { copy(s.ringbuffer[pos:], word[:uint(len)]) } else { len = transformDictionaryWord(s.ringbuffer[pos:], word, int(len), trans, transform_idx) } pos += int(len) s.meta_block_remaining_len -= int(len) if pos >= s.ringbuffer_size { s.state = stateCommandPostWrite1 goto saveStateAndReturn } } else { return decoderErrorFormatTransform } } else { return decoderErrorFormatDictionary } } else { var src_start int = (pos - s.distance_code) & s.ringbuffer_mask var copy_dst []byte copy_dst = s.ringbuffer[pos:] var copy_src []byte copy_src = s.ringbuffer[src_start:] var dst_end int = pos + i var src_end int = src_start + i /* Update the recent distances cache. */ s.dist_rb[s.dist_rb_idx&3] = s.distance_code s.dist_rb_idx++ s.meta_block_remaining_len -= i /* There are 32+ bytes of slack in the ring-buffer allocation. Also, we have 16 short codes, that make these 16 bytes irrelevant in the ring-buffer. Let's copy over them as a first guess. */ copy(copy_dst, copy_src[:16]) if src_end > pos && dst_end > src_start { /* Regions intersect. */ goto CommandPostWrapCopy } if dst_end >= s.ringbuffer_size || src_end >= s.ringbuffer_size { /* At least one region wraps. */ goto CommandPostWrapCopy } pos += i if i > 16 { if i > 32 { copy(copy_dst[16:], copy_src[16:][:uint(i-16)]) } else { /* This branch covers about 45% cases. Fixed size short copy allows more compiler optimizations. */ copy(copy_dst[16:], copy_src[16:][:16]) } } } if s.meta_block_remaining_len <= 0 { /* Next metablock, if any. */ s.state = stateMetablockDone goto saveStateAndReturn } else { goto CommandBegin } CommandPostWrapCopy: { var wrap_guard int = s.ringbuffer_size - pos for { i-- if i < 0 { break } s.ringbuffer[pos] = s.ringbuffer[(pos-s.distance_code)&s.ringbuffer_mask] pos++ wrap_guard-- if wrap_guard == 0 { s.state = stateCommandPostWrite2 goto saveStateAndReturn } } } if s.meta_block_remaining_len <= 0 { /* Next metablock, if any. */ s.state = stateMetablockDone goto saveStateAndReturn } else { goto CommandBegin } saveStateAndReturn: s.pos = pos s.loop_counter = i return result } func processCommands(s *Reader) int { return processCommandsInternal(0, s) } func safeProcessCommands(s *Reader) int { return processCommandsInternal(1, s) } /* Returns the maximum number of distance symbols which can only represent distances not exceeding BROTLI_MAX_ALLOWED_DISTANCE. */ var maxDistanceSymbol_bound = [maxNpostfix + 1]uint32{0, 4, 12, 28} var maxDistanceSymbol_diff = [maxNpostfix + 1]uint32{73, 126, 228, 424} func maxDistanceSymbol(ndirect uint32, npostfix uint32) uint32 { var postfix uint32 = 1 << npostfix if ndirect < maxDistanceSymbol_bound[npostfix] { return ndirect + maxDistanceSymbol_diff[npostfix] + postfix } else if ndirect > maxDistanceSymbol_bound[npostfix]+postfix { return ndirect + maxDistanceSymbol_diff[npostfix] } else { return maxDistanceSymbol_bound[npostfix] + maxDistanceSymbol_diff[npostfix] + postfix } } /* Invariant: input stream is never overconsumed: - invalid input implies that the whole stream is invalid -> any amount of input could be read and discarded - when result is "needs more input", then at least one more byte is REQUIRED to complete decoding; all input data MUST be consumed by decoder, so client could swap the input buffer - when result is "needs more output" decoder MUST ensure that it doesn't hold more than 7 bits in bit reader; this saves client from swapping input buffer ahead of time - when result is "success" decoder MUST return all unused data back to input buffer; this is possible because the invariant is held on enter */ func decoderDecompressStream(s *Reader, available_in *uint, next_in *[]byte, available_out *uint, next_out *[]byte) int { var result int = decoderSuccess var br *bitReader = &s.br /* Do not try to process further in a case of unrecoverable error. */ if int(s.error_code) < 0 { return decoderResultError } if *available_out != 0 && (next_out == nil || *next_out == nil) { return saveErrorCode(s, decoderErrorInvalidArguments) } if *available_out == 0 { next_out = nil } if s.buffer_length == 0 { /* Just connect bit reader to input stream. */ br.input_len = *available_in br.input = *next_in br.byte_pos = 0 } else { /* At least one byte of input is required. More than one byte of input may be required to complete the transaction -> reading more data must be done in a loop -> do it in a main loop. */ result = decoderNeedsMoreInput br.input = s.buffer.u8[:] br.byte_pos = 0 } /* State machine */ for { if result != decoderSuccess { /* Error, needs more input/output. */ if result == decoderNeedsMoreInput { if s.ringbuffer != nil { /* Pro-actively push output. */ var intermediate_result int = writeRingBuffer(s, available_out, next_out, nil, true) /* WriteRingBuffer checks s->meta_block_remaining_len validity. */ if int(intermediate_result) < 0 { result = intermediate_result break } } if s.buffer_length != 0 { /* Used with internal buffer. */ if br.byte_pos == br.input_len { /* Successfully finished read transaction. Accumulator contains less than 8 bits, because internal buffer is expanded byte-by-byte until it is enough to complete read. */ s.buffer_length = 0 /* Switch to input stream and restart. */ result = decoderSuccess br.input_len = *available_in br.input = *next_in br.byte_pos = 0 continue } else if *available_in != 0 { /* Not enough data in buffer, but can take one more byte from input stream. */ result = decoderSuccess s.buffer.u8[s.buffer_length] = (*next_in)[0] s.buffer_length++ br.input_len = uint(s.buffer_length) *next_in = (*next_in)[1:] (*available_in)-- /* Retry with more data in buffer. */ continue } /* Can't finish reading and no more input. */ break /* Input stream doesn't contain enough input. */ } else { /* Copy tail to internal buffer and return. */ *next_in = br.input[br.byte_pos:] *available_in = br.input_len - br.byte_pos for *available_in != 0 { s.buffer.u8[s.buffer_length] = (*next_in)[0] s.buffer_length++ *next_in = (*next_in)[1:] (*available_in)-- } break } } /* Unreachable. */ /* Fail or needs more output. */ if s.buffer_length != 0 { /* Just consumed the buffered input and produced some output. Otherwise it would result in "needs more input". Reset internal buffer. */ s.buffer_length = 0 } else { /* Using input stream in last iteration. When decoder switches to input stream it has less than 8 bits in accumulator, so it is safe to return unused accumulator bits there. */ bitReaderUnload(br) *available_in = br.input_len - br.byte_pos *next_in = br.input[br.byte_pos:] } break } switch s.state { /* Prepare to the first read. */ case stateUninited: if !warmupBitReader(br) { result = decoderNeedsMoreInput break } /* Decode window size. */ result = decodeWindowBits(s, br) /* Reads 1..8 bits. */ if result != decoderSuccess { break } if s.large_window { s.state = stateLargeWindowBits break } s.state = stateInitialize case stateLargeWindowBits: if !safeReadBits(br, 6, &s.window_bits) { result = decoderNeedsMoreInput break } if s.window_bits < largeMinWbits || s.window_bits > largeMaxWbits { result = decoderErrorFormatWindowBits break } s.state = stateInitialize fallthrough /* Maximum distance, see section 9.1. of the spec. */ /* Fall through. */ case stateInitialize: s.max_backward_distance = (1 << s.window_bits) - windowGap /* Allocate memory for both block_type_trees and block_len_trees. */ s.block_type_trees = make([]huffmanCode, (3 * (huffmanMaxSize258 + huffmanMaxSize26))) if s.block_type_trees == nil { result = decoderErrorAllocBlockTypeTrees break } s.block_len_trees = s.block_type_trees[3*huffmanMaxSize258:] s.state = stateMetablockBegin fallthrough /* Fall through. */ case stateMetablockBegin: decoderStateMetablockBegin(s) s.state = stateMetablockHeader fallthrough /* Fall through. */ case stateMetablockHeader: result = decodeMetaBlockLength(s, br) /* Reads 2 - 31 bits. */ if result != decoderSuccess { break } if s.is_metadata != 0 || s.is_uncompressed != 0 { if !bitReaderJumpToByteBoundary(br) { result = decoderErrorFormatPadding1 break } } if s.is_metadata != 0 { s.state = stateMetadata break } if s.meta_block_remaining_len == 0 { s.state = stateMetablockDone break } calculateRingBufferSize(s) if s.is_uncompressed != 0 { s.state = stateUncompressed break } s.loop_counter = 0 s.state = stateHuffmanCode0 case stateUncompressed: result = copyUncompressedBlockToOutput(available_out, next_out, nil, s) if result == decoderSuccess { s.state = stateMetablockDone } case stateMetadata: for ; s.meta_block_remaining_len > 0; s.meta_block_remaining_len-- { var bits uint32 /* Read one byte and ignore it. */ if !safeReadBits(br, 8, &bits) { result = decoderNeedsMoreInput break } } if result == decoderSuccess { s.state = stateMetablockDone } case stateHuffmanCode0: if s.loop_counter >= 3 { s.state = stateMetablockHeader2 break } /* Reads 1..11 bits. */ result = decodeVarLenUint8(s, br, &s.num_block_types[s.loop_counter]) if result != decoderSuccess { break } s.num_block_types[s.loop_counter]++ if s.num_block_types[s.loop_counter] < 2 { s.loop_counter++ break } s.state = stateHuffmanCode1 fallthrough case stateHuffmanCode1: { var alphabet_size uint32 = s.num_block_types[s.loop_counter] + 2 var tree_offset int = s.loop_counter * huffmanMaxSize258 result = readHuffmanCode(alphabet_size, alphabet_size, s.block_type_trees[tree_offset:], nil, s) if result != decoderSuccess { break } s.state = stateHuffmanCode2 } fallthrough case stateHuffmanCode2: { var alphabet_size uint32 = numBlockLenSymbols var tree_offset int = s.loop_counter * huffmanMaxSize26 result = readHuffmanCode(alphabet_size, alphabet_size, s.block_len_trees[tree_offset:], nil, s) if result != decoderSuccess { break } s.state = stateHuffmanCode3 } fallthrough case stateHuffmanCode3: var tree_offset int = s.loop_counter * huffmanMaxSize26 if !safeReadBlockLength(s, &s.block_length[s.loop_counter], s.block_len_trees[tree_offset:], br) { result = decoderNeedsMoreInput break } s.loop_counter++ s.state = stateHuffmanCode0 case stateMetablockHeader2: { var bits uint32 if !safeReadBits(br, 6, &bits) { result = decoderNeedsMoreInput break } s.distance_postfix_bits = bits & bitMask(2) bits >>= 2 s.num_direct_distance_codes = numDistanceShortCodes + (bits << s.distance_postfix_bits) s.distance_postfix_mask = int(bitMask(s.distance_postfix_bits)) s.context_modes = make([]byte, uint(s.num_block_types[0])) if s.context_modes == nil { result = decoderErrorAllocContextModes break } s.loop_counter = 0 s.state = stateContextModes } fallthrough case stateContextModes: result = readContextModes(s) if result != decoderSuccess { break } s.state = stateContextMap1 fallthrough case stateContextMap1: result = decodeContextMap(s.num_block_types[0]<= 3 { prepareLiteralDecoding(s) s.dist_context_map_slice = s.dist_context_map s.htree_command = []huffmanCode(s.insert_copy_hgroup.htrees[0]) if !ensureRingBuffer(s) { result = decoderErrorAllocRingBuffer2 break } s.state = stateCommandBegin } case stateCommandBegin, stateCommandInner, stateCommandPostDecodeLiterals, stateCommandPostWrapCopy: result = processCommands(s) if result == decoderNeedsMoreInput { result = safeProcessCommands(s) } case stateCommandInnerWrite, stateCommandPostWrite1, stateCommandPostWrite2: result = writeRingBuffer(s, available_out, next_out, nil, false) if result != decoderSuccess { break } wrapRingBuffer(s) if s.ringbuffer_size == 1<