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540 lines
21 KiB
C++
540 lines
21 KiB
C++
// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "net/http2/hpack/huffman/hpack_huffman_decoder.h"
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#include <bitset>
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#include <limits>
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#include "base/logging.h"
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// Terminology:
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//
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// Symbol - a plain text (unencoded) character (uint8), or the End-of-String
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// (EOS) symbol, 256.
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//
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// Code - the sequence of bits used to encode a symbol, varying in length from
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// 5 bits for the most common symbols (e.g. '0', '1', and 'a'), to
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// 30 bits for the least common (e.g. the EOS symbol).
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// For those symbols whose codes have the same length, their code values
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// are sorted such that the lower symbol value has a lower code value.
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//
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// Canonical - a symbol's cardinal value when sorted first by code length, and
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// then by symbol value. For example, canonical 0 is for ASCII '0'
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// (uint8 value 0x30), which is the first of the symbols whose code
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// is 5 bits long, and the last canonical is EOS, which is the last
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// of the symbols whose code is 30 bits long.
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// TODO(jamessynge): Remove use of binary literals, that is a C++ 14 feature.
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namespace net {
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namespace {
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// HuffmanCode is used to store the codes associated with symbols (a pattern of
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// from 5 to 30 bits).
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typedef uint32_t HuffmanCode;
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// HuffmanCodeBitCount is used to store a count of bits in a code.
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typedef uint16_t HuffmanCodeBitCount;
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// HuffmanCodeBitSet is used for producing a string version of a code because
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// std::bitset logs nicely.
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typedef std::bitset<32> HuffmanCodeBitSet;
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typedef std::bitset<64> HuffmanAccumulatorBitSet;
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static constexpr HuffmanCodeBitCount kMinCodeBitCount = 5;
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static constexpr HuffmanCodeBitCount kMaxCodeBitCount = 30;
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static constexpr HuffmanCodeBitCount kHuffmanCodeBitCount =
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std::numeric_limits<HuffmanCode>::digits;
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static_assert(std::numeric_limits<HuffmanCode>::digits >= kMaxCodeBitCount,
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"HuffmanCode isn't big enough.");
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static_assert(std::numeric_limits<HuffmanAccumulator>::digits >=
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kMaxCodeBitCount,
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"HuffmanAccumulator isn't big enough.");
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static constexpr HuffmanAccumulatorBitCount kHuffmanAccumulatorBitCount =
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std::numeric_limits<HuffmanAccumulator>::digits;
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static constexpr HuffmanAccumulatorBitCount kExtraAccumulatorBitCount =
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kHuffmanAccumulatorBitCount - kHuffmanCodeBitCount;
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// PrefixInfo holds info about a group of codes that are all of the same length.
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struct PrefixInfo {
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// Given the leading bits (32 in this case) of the encoded string, and that
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// they start with a code of length |code_length|, return the corresponding
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// canonical for that leading code.
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uint32_t DecodeToCanonical(HuffmanCode bits) const {
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// What is the position of the canonical symbol being decoded within
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// the canonical symbols of |length|?
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HuffmanCode ordinal_in_length =
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((bits - first_code) >> (kHuffmanCodeBitCount - code_length));
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// Combined with |canonical| to produce the position of the canonical symbol
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// being decoded within all of the canonical symbols.
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return first_canonical + ordinal_in_length;
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}
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const HuffmanCode first_code; // First code of this length, left justified in
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// the field (i.e. the first bit of the code is
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// the high-order bit).
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const uint16_t code_length; // Length of the prefix code |base|.
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const uint16_t first_canonical; // First canonical symbol of this length.
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};
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inline std::ostream& operator<<(std::ostream& out, const PrefixInfo& v) {
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return out << "{first_code: " << HuffmanCodeBitSet(v.first_code)
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<< ", code_length: " << v.code_length
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<< ", first_canonical: " << v.first_canonical << "}";
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}
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// Given |value|, a sequence of the leading bits remaining to be decoded,
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// figure out which group of canonicals (by code length) that value starts
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// with. This function was generated.
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PrefixInfo PrefixToInfo(HuffmanCode value) {
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if (value < 0b10111000000000000000000000000000) {
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if (value < 0b01010000000000000000000000000000) {
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return {0b00000000000000000000000000000000, 5, 0};
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} else {
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return {0b01010000000000000000000000000000, 6, 10};
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}
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} else {
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if (value < 0b11111110000000000000000000000000) {
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if (value < 0b11111000000000000000000000000000) {
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return {0b10111000000000000000000000000000, 7, 36};
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} else {
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return {0b11111000000000000000000000000000, 8, 68};
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}
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} else {
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if (value < 0b11111111110000000000000000000000) {
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if (value < 0b11111111101000000000000000000000) {
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if (value < 0b11111111010000000000000000000000) {
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return {0b11111110000000000000000000000000, 10, 74};
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} else {
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return {0b11111111010000000000000000000000, 11, 79};
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}
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} else {
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return {0b11111111101000000000000000000000, 12, 82};
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}
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} else {
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if (value < 0b11111111111111100000000000000000) {
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if (value < 0b11111111111110000000000000000000) {
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if (value < 0b11111111111100000000000000000000) {
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return {0b11111111110000000000000000000000, 13, 84};
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} else {
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return {0b11111111111100000000000000000000, 14, 90};
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}
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} else {
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return {0b11111111111110000000000000000000, 15, 92};
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}
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} else {
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if (value < 0b11111111111111110100100000000000) {
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if (value < 0b11111111111111101110000000000000) {
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if (value < 0b11111111111111100110000000000000) {
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return {0b11111111111111100000000000000000, 19, 95};
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} else {
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return {0b11111111111111100110000000000000, 20, 98};
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}
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} else {
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return {0b11111111111111101110000000000000, 21, 106};
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}
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} else {
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if (value < 0b11111111111111111110101000000000) {
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if (value < 0b11111111111111111011000000000000) {
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return {0b11111111111111110100100000000000, 22, 119};
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} else {
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return {0b11111111111111111011000000000000, 23, 145};
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}
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} else {
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if (value < 0b11111111111111111111101111000000) {
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if (value < 0b11111111111111111111100000000000) {
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if (value < 0b11111111111111111111011000000000) {
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return {0b11111111111111111110101000000000, 24, 174};
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} else {
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return {0b11111111111111111111011000000000, 25, 186};
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}
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} else {
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return {0b11111111111111111111100000000000, 26, 190};
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}
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} else {
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if (value < 0b11111111111111111111111111110000) {
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if (value < 0b11111111111111111111111000100000) {
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return {0b11111111111111111111101111000000, 27, 205};
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} else {
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return {0b11111111111111111111111000100000, 28, 224};
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}
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} else {
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return {0b11111111111111111111111111110000, 30, 253};
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}
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}
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}
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}
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}
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}
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}
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}
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}
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// Mapping from canonical symbol (0 to 255) to actual symbol.
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// clang-format off
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constexpr unsigned char kCanonicalToSymbol[] = {
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'0', '1', '2', 'a', 'c', 'e', 'i', 'o',
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's', 't', 0x20, '%', '-', '.', '/', '3',
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'4', '5', '6', '7', '8', '9', '=', 'A',
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'_', 'b', 'd', 'f', 'g', 'h', 'l', 'm',
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'n', 'p', 'r', 'u', ':', 'B', 'C', 'D',
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'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
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'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
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'U', 'V', 'W', 'Y', 'j', 'k', 'q', 'v',
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'w', 'x', 'y', 'z', '&', '*', ',', ';',
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'X', 'Z', '!', '\"', '(', ')', '?', '\'',
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'+', '|', '#', '>', 0x00, '$', '@', '[',
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']', '~', '^', '}', '<', '`', '{', '\\',
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0xc3, 0xd0, 0x80, 0x82, 0x83, 0xa2, 0xb8, 0xc2,
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0xe0, 0xe2, 0x99, 0xa1, 0xa7, 0xac, 0xb0, 0xb1,
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0xb3, 0xd1, 0xd8, 0xd9, 0xe3, 0xe5, 0xe6, 0x81,
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0x84, 0x85, 0x86, 0x88, 0x92, 0x9a, 0x9c, 0xa0,
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0xa3, 0xa4, 0xa9, 0xaa, 0xad, 0xb2, 0xb5, 0xb9,
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0xba, 0xbb, 0xbd, 0xbe, 0xc4, 0xc6, 0xe4, 0xe8,
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0xe9, 0x01, 0x87, 0x89, 0x8a, 0x8b, 0x8c, 0x8d,
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0x8f, 0x93, 0x95, 0x96, 0x97, 0x98, 0x9b, 0x9d,
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0x9e, 0xa5, 0xa6, 0xa8, 0xae, 0xaf, 0xb4, 0xb6,
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0xb7, 0xbc, 0xbf, 0xc5, 0xe7, 0xef, 0x09, 0x8e,
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0x90, 0x91, 0x94, 0x9f, 0xab, 0xce, 0xd7, 0xe1,
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0xec, 0xed, 0xc7, 0xcf, 0xea, 0xeb, 0xc0, 0xc1,
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0xc8, 0xc9, 0xca, 0xcd, 0xd2, 0xd5, 0xda, 0xdb,
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0xee, 0xf0, 0xf2, 0xf3, 0xff, 0xcb, 0xcc, 0xd3,
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0xd4, 0xd6, 0xdd, 0xde, 0xdf, 0xf1, 0xf4, 0xf5,
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0xf6, 0xf7, 0xf8, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe,
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0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x0b,
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0x0c, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14,
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0x15, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d,
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0x1e, 0x1f, 0x7f, 0xdc, 0xf9, 0x0a, 0x0d, 0x16,
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};
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// clang-format on
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constexpr size_t kShortCodeTableSize = 124;
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struct ShortCodeInfo {
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uint8_t symbol;
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uint8_t length;
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} kShortCodeTable[kShortCodeTableSize] = {
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{0x30, 5}, // Match: 0b0000000, Symbol: 0
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{0x30, 5}, // Match: 0b0000001, Symbol: 0
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{0x30, 5}, // Match: 0b0000010, Symbol: 0
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{0x30, 5}, // Match: 0b0000011, Symbol: 0
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{0x31, 5}, // Match: 0b0000100, Symbol: 1
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{0x31, 5}, // Match: 0b0000101, Symbol: 1
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{0x31, 5}, // Match: 0b0000110, Symbol: 1
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{0x31, 5}, // Match: 0b0000111, Symbol: 1
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{0x32, 5}, // Match: 0b0001000, Symbol: 2
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{0x32, 5}, // Match: 0b0001001, Symbol: 2
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{0x32, 5}, // Match: 0b0001010, Symbol: 2
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{0x32, 5}, // Match: 0b0001011, Symbol: 2
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{0x61, 5}, // Match: 0b0001100, Symbol: a
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{0x61, 5}, // Match: 0b0001101, Symbol: a
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{0x61, 5}, // Match: 0b0001110, Symbol: a
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{0x61, 5}, // Match: 0b0001111, Symbol: a
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{0x63, 5}, // Match: 0b0010000, Symbol: c
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{0x63, 5}, // Match: 0b0010001, Symbol: c
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{0x63, 5}, // Match: 0b0010010, Symbol: c
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{0x63, 5}, // Match: 0b0010011, Symbol: c
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{0x65, 5}, // Match: 0b0010100, Symbol: e
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{0x65, 5}, // Match: 0b0010101, Symbol: e
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{0x65, 5}, // Match: 0b0010110, Symbol: e
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{0x65, 5}, // Match: 0b0010111, Symbol: e
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{0x69, 5}, // Match: 0b0011000, Symbol: i
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{0x69, 5}, // Match: 0b0011001, Symbol: i
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{0x69, 5}, // Match: 0b0011010, Symbol: i
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{0x69, 5}, // Match: 0b0011011, Symbol: i
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{0x6f, 5}, // Match: 0b0011100, Symbol: o
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{0x6f, 5}, // Match: 0b0011101, Symbol: o
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{0x6f, 5}, // Match: 0b0011110, Symbol: o
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{0x6f, 5}, // Match: 0b0011111, Symbol: o
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{0x73, 5}, // Match: 0b0100000, Symbol: s
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{0x73, 5}, // Match: 0b0100001, Symbol: s
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{0x73, 5}, // Match: 0b0100010, Symbol: s
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{0x73, 5}, // Match: 0b0100011, Symbol: s
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{0x74, 5}, // Match: 0b0100100, Symbol: t
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{0x74, 5}, // Match: 0b0100101, Symbol: t
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{0x74, 5}, // Match: 0b0100110, Symbol: t
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{0x74, 5}, // Match: 0b0100111, Symbol: t
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{0x20, 6}, // Match: 0b0101000, Symbol: (space)
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{0x20, 6}, // Match: 0b0101001, Symbol: (space)
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{0x25, 6}, // Match: 0b0101010, Symbol: %
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{0x25, 6}, // Match: 0b0101011, Symbol: %
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{0x2d, 6}, // Match: 0b0101100, Symbol: -
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{0x2d, 6}, // Match: 0b0101101, Symbol: -
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{0x2e, 6}, // Match: 0b0101110, Symbol: .
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{0x2e, 6}, // Match: 0b0101111, Symbol: .
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{0x2f, 6}, // Match: 0b0110000, Symbol: /
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{0x2f, 6}, // Match: 0b0110001, Symbol: /
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{0x33, 6}, // Match: 0b0110010, Symbol: 3
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{0x33, 6}, // Match: 0b0110011, Symbol: 3
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{0x34, 6}, // Match: 0b0110100, Symbol: 4
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{0x34, 6}, // Match: 0b0110101, Symbol: 4
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{0x35, 6}, // Match: 0b0110110, Symbol: 5
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{0x35, 6}, // Match: 0b0110111, Symbol: 5
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{0x36, 6}, // Match: 0b0111000, Symbol: 6
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{0x36, 6}, // Match: 0b0111001, Symbol: 6
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{0x37, 6}, // Match: 0b0111010, Symbol: 7
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{0x37, 6}, // Match: 0b0111011, Symbol: 7
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{0x38, 6}, // Match: 0b0111100, Symbol: 8
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{0x38, 6}, // Match: 0b0111101, Symbol: 8
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{0x39, 6}, // Match: 0b0111110, Symbol: 9
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{0x39, 6}, // Match: 0b0111111, Symbol: 9
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{0x3d, 6}, // Match: 0b1000000, Symbol: =
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{0x3d, 6}, // Match: 0b1000001, Symbol: =
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{0x41, 6}, // Match: 0b1000010, Symbol: A
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{0x41, 6}, // Match: 0b1000011, Symbol: A
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{0x5f, 6}, // Match: 0b1000100, Symbol: _
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{0x5f, 6}, // Match: 0b1000101, Symbol: _
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{0x62, 6}, // Match: 0b1000110, Symbol: b
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{0x62, 6}, // Match: 0b1000111, Symbol: b
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{0x64, 6}, // Match: 0b1001000, Symbol: d
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{0x64, 6}, // Match: 0b1001001, Symbol: d
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{0x66, 6}, // Match: 0b1001010, Symbol: f
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{0x66, 6}, // Match: 0b1001011, Symbol: f
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{0x67, 6}, // Match: 0b1001100, Symbol: g
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{0x67, 6}, // Match: 0b1001101, Symbol: g
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{0x68, 6}, // Match: 0b1001110, Symbol: h
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{0x68, 6}, // Match: 0b1001111, Symbol: h
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{0x6c, 6}, // Match: 0b1010000, Symbol: l
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{0x6c, 6}, // Match: 0b1010001, Symbol: l
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{0x6d, 6}, // Match: 0b1010010, Symbol: m
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{0x6d, 6}, // Match: 0b1010011, Symbol: m
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{0x6e, 6}, // Match: 0b1010100, Symbol: n
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{0x6e, 6}, // Match: 0b1010101, Symbol: n
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{0x70, 6}, // Match: 0b1010110, Symbol: p
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{0x70, 6}, // Match: 0b1010111, Symbol: p
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{0x72, 6}, // Match: 0b1011000, Symbol: r
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{0x72, 6}, // Match: 0b1011001, Symbol: r
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{0x75, 6}, // Match: 0b1011010, Symbol: u
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{0x75, 6}, // Match: 0b1011011, Symbol: u
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{0x3a, 7}, // Match: 0b1011100, Symbol: :
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{0x42, 7}, // Match: 0b1011101, Symbol: B
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{0x43, 7}, // Match: 0b1011110, Symbol: C
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{0x44, 7}, // Match: 0b1011111, Symbol: D
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{0x45, 7}, // Match: 0b1100000, Symbol: E
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{0x46, 7}, // Match: 0b1100001, Symbol: F
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{0x47, 7}, // Match: 0b1100010, Symbol: G
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{0x48, 7}, // Match: 0b1100011, Symbol: H
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{0x49, 7}, // Match: 0b1100100, Symbol: I
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{0x4a, 7}, // Match: 0b1100101, Symbol: J
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{0x4b, 7}, // Match: 0b1100110, Symbol: K
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{0x4c, 7}, // Match: 0b1100111, Symbol: L
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{0x4d, 7}, // Match: 0b1101000, Symbol: M
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{0x4e, 7}, // Match: 0b1101001, Symbol: N
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{0x4f, 7}, // Match: 0b1101010, Symbol: O
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{0x50, 7}, // Match: 0b1101011, Symbol: P
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{0x51, 7}, // Match: 0b1101100, Symbol: Q
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{0x52, 7}, // Match: 0b1101101, Symbol: R
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{0x53, 7}, // Match: 0b1101110, Symbol: S
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{0x54, 7}, // Match: 0b1101111, Symbol: T
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{0x55, 7}, // Match: 0b1110000, Symbol: U
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{0x56, 7}, // Match: 0b1110001, Symbol: V
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{0x57, 7}, // Match: 0b1110010, Symbol: W
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{0x59, 7}, // Match: 0b1110011, Symbol: Y
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{0x6a, 7}, // Match: 0b1110100, Symbol: j
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{0x6b, 7}, // Match: 0b1110101, Symbol: k
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{0x71, 7}, // Match: 0b1110110, Symbol: q
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{0x76, 7}, // Match: 0b1110111, Symbol: v
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{0x77, 7}, // Match: 0b1111000, Symbol: w
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{0x78, 7}, // Match: 0b1111001, Symbol: x
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{0x79, 7}, // Match: 0b1111010, Symbol: y
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{0x7a, 7}, // Match: 0b1111011, Symbol: z
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};
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} // namespace
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HuffmanBitBuffer::HuffmanBitBuffer() {
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Reset();
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}
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void HuffmanBitBuffer::Reset() {
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accumulator_ = 0;
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count_ = 0;
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}
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size_t HuffmanBitBuffer::AppendBytes(Http2StringPiece input) {
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HuffmanAccumulatorBitCount free_cnt = free_count();
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size_t bytes_available = input.size();
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if (free_cnt < 8 || bytes_available == 0) {
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return 0;
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}
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// Top up |accumulator_| until there isn't room for a whole byte.
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size_t bytes_used = 0;
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auto* ptr = reinterpret_cast<const uint8_t*>(input.data());
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do {
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auto b = static_cast<HuffmanAccumulator>(*ptr++);
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free_cnt -= 8;
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accumulator_ |= (b << free_cnt);
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++bytes_used;
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} while (free_cnt >= 8 && bytes_used < bytes_available);
|
|
count_ += (bytes_used * 8);
|
|
return bytes_used;
|
|
}
|
|
|
|
HuffmanAccumulatorBitCount HuffmanBitBuffer::free_count() const {
|
|
return kHuffmanAccumulatorBitCount - count_;
|
|
}
|
|
|
|
void HuffmanBitBuffer::ConsumeBits(HuffmanAccumulatorBitCount code_length) {
|
|
DCHECK_LE(code_length, count_);
|
|
accumulator_ <<= code_length;
|
|
count_ -= code_length;
|
|
}
|
|
|
|
bool HuffmanBitBuffer::InputProperlyTerminated() const {
|
|
auto cnt = count();
|
|
if (cnt < 8) {
|
|
if (cnt == 0) {
|
|
return true;
|
|
}
|
|
HuffmanAccumulator expected = ~(~HuffmanAccumulator() >> cnt);
|
|
// We expect all the bits below the high order |cnt| bits of accumulator_
|
|
// to be cleared as we perform left shift operations while decoding.
|
|
DCHECK_EQ(accumulator_ & ~expected, 0u)
|
|
<< "\n expected: " << HuffmanAccumulatorBitSet(expected) << "\n "
|
|
<< *this;
|
|
return accumulator_ == expected;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
Http2String HuffmanBitBuffer::DebugString() const {
|
|
std::stringstream ss;
|
|
ss << "{accumulator: " << HuffmanAccumulatorBitSet(accumulator_)
|
|
<< "; count: " << count_ << "}";
|
|
return ss.str();
|
|
}
|
|
|
|
HpackHuffmanDecoder::HpackHuffmanDecoder() {}
|
|
|
|
HpackHuffmanDecoder::~HpackHuffmanDecoder() {}
|
|
|
|
bool HpackHuffmanDecoder::Decode(Http2StringPiece input, Http2String* output) {
|
|
return DecodeShortCodesFirst(input, output);
|
|
}
|
|
|
|
// "Legacy" decoder, used until cl/129771019 submitted, which added
|
|
// DecodeShortCodesFirst() as primary decoder method.
|
|
// TODO(jamessynge): Remove this once satisfied that there is no going back.
|
|
bool HpackHuffmanDecoder::DecodeWithIfTreeAndStruct(Http2StringPiece input,
|
|
Http2String* output) {
|
|
DVLOG(1) << "HpackHuffmanDecoder::DecodeWithIfTreeAndStruct";
|
|
|
|
// Fill bit_buffer_ from input.
|
|
input.remove_prefix(bit_buffer_.AppendBytes(input));
|
|
|
|
while (true) {
|
|
DVLOG(3) << "Enter Decode Loop, bit_buffer_: " << bit_buffer_;
|
|
|
|
HuffmanCode code_prefix = bit_buffer_.value() >> kExtraAccumulatorBitCount;
|
|
DVLOG(3) << "code_prefix: " << HuffmanCodeBitSet(code_prefix);
|
|
|
|
PrefixInfo prefix_info = PrefixToInfo(code_prefix);
|
|
DVLOG(3) << "prefix_info: " << prefix_info;
|
|
DCHECK_LE(kMinCodeBitCount, prefix_info.code_length);
|
|
DCHECK_LE(prefix_info.code_length, kMaxCodeBitCount);
|
|
|
|
if (prefix_info.code_length <= bit_buffer_.count()) {
|
|
// We have enough bits for one code.
|
|
uint32_t canonical = prefix_info.DecodeToCanonical(code_prefix);
|
|
if (canonical < 256) {
|
|
// Valid code.
|
|
char c = kCanonicalToSymbol[canonical];
|
|
output->push_back(c);
|
|
bit_buffer_.ConsumeBits(prefix_info.code_length);
|
|
continue;
|
|
}
|
|
// Encoder is not supposed to explicity encode the EOS symbol.
|
|
DLOG(ERROR) << "EOS explicitly encoded!\n " << bit_buffer_ << "\n "
|
|
<< prefix_info;
|
|
return false;
|
|
}
|
|
// bit_buffer_ doesn't have enough bits in it to decode the next symbol.
|
|
// Append to it as many bytes as are available AND fit.
|
|
size_t byte_count = bit_buffer_.AppendBytes(input);
|
|
if (byte_count == 0) {
|
|
DCHECK_EQ(input.size(), 0u);
|
|
return true;
|
|
}
|
|
input.remove_prefix(byte_count);
|
|
}
|
|
}
|
|
|
|
bool HpackHuffmanDecoder::DecodeShortCodesFirst(Http2StringPiece input,
|
|
Http2String* output) {
|
|
DVLOG(1) << "HpackHuffmanDecoder::DecodeShortCodesFirst";
|
|
|
|
// Fill bit_buffer_ from input.
|
|
input.remove_prefix(bit_buffer_.AppendBytes(input));
|
|
|
|
while (true) {
|
|
DVLOG(3) << "Enter Decode Loop, bit_buffer_: " << bit_buffer_;
|
|
if (bit_buffer_.count() >= 7) {
|
|
// Get high 7 bits of the bit buffer, see if that contains a complete
|
|
// code of 5, 6 or 7 bits.
|
|
uint8_t short_code =
|
|
bit_buffer_.value() >> (kHuffmanAccumulatorBitCount - 7);
|
|
DCHECK_LT(short_code, 128);
|
|
if (short_code < kShortCodeTableSize) {
|
|
ShortCodeInfo info = kShortCodeTable[short_code];
|
|
bit_buffer_.ConsumeBits(info.length);
|
|
output->push_back(static_cast<char>(info.symbol));
|
|
continue;
|
|
}
|
|
// The code is more than 7 bits long. Use PrefixToInfo, etc. to decode
|
|
// longer codes.
|
|
} else {
|
|
// We may have (mostly) drained bit_buffer_. If we can top it up, try
|
|
// using the table decoder above.
|
|
size_t byte_count = bit_buffer_.AppendBytes(input);
|
|
if (byte_count > 0) {
|
|
input.remove_prefix(byte_count);
|
|
continue;
|
|
}
|
|
}
|
|
|
|
HuffmanCode code_prefix = bit_buffer_.value() >> kExtraAccumulatorBitCount;
|
|
DVLOG(3) << "code_prefix: " << HuffmanCodeBitSet(code_prefix);
|
|
|
|
PrefixInfo prefix_info = PrefixToInfo(code_prefix);
|
|
DVLOG(3) << "prefix_info: " << prefix_info;
|
|
DCHECK_LE(kMinCodeBitCount, prefix_info.code_length);
|
|
DCHECK_LE(prefix_info.code_length, kMaxCodeBitCount);
|
|
|
|
if (prefix_info.code_length <= bit_buffer_.count()) {
|
|
// We have enough bits for one code.
|
|
uint32_t canonical = prefix_info.DecodeToCanonical(code_prefix);
|
|
if (canonical < 256) {
|
|
// Valid code.
|
|
char c = kCanonicalToSymbol[canonical];
|
|
output->push_back(c);
|
|
bit_buffer_.ConsumeBits(prefix_info.code_length);
|
|
continue;
|
|
}
|
|
// Encoder is not supposed to explicity encode the EOS symbol.
|
|
DLOG(ERROR) << "EOS explicitly encoded!\n " << bit_buffer_ << "\n "
|
|
<< prefix_info;
|
|
return false;
|
|
}
|
|
// bit_buffer_ doesn't have enough bits in it to decode the next symbol.
|
|
// Append to it as many bytes as are available AND fit.
|
|
size_t byte_count = bit_buffer_.AppendBytes(input);
|
|
if (byte_count == 0) {
|
|
DCHECK_EQ(input.size(), 0u);
|
|
return true;
|
|
}
|
|
input.remove_prefix(byte_count);
|
|
}
|
|
}
|
|
|
|
Http2String HpackHuffmanDecoder::DebugString() const {
|
|
return bit_buffer_.DebugString();
|
|
}
|
|
|
|
} // namespace net
|