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src/qpack_huffman_enc.hrl
%%% -*- erlang -*-
%%%
%%% This file is part of erlang_qpack released under the Apache 2 license.
%%% See the NOTICE for more information.
%%%
%%% Copyright (c) 2024-2026 Benoit Chesneau
%%%
%%% @doc Huffman encoding lookup table for QPACK (RFC 9204).
%%%
%%% RFC 7541 Appendix B defines the Huffman code table used by both
%%% HPACK (HTTP/2) and QPACK (HTTP/3). This file provides pre-computed
%%% lookup for fast encoding.
%%% @end
%% Huffman encoding table: {Code, BitLength}
%% Each entry is {huffman code bits, number of bits}
%% The codes are stored MSB-first as integers.
-define(HUFFMAN_ENCODE_TABLE, {
%% 0-15 (control characters)
{16#1ff8, 13}, %% 0
{16#7fffd8, 23}, %% 1
{16#fffffe2, 28}, %% 2
{16#fffffe3, 28}, %% 3
{16#fffffe4, 28}, %% 4
{16#fffffe5, 28}, %% 5
{16#fffffe6, 28}, %% 6
{16#fffffe7, 28}, %% 7
{16#fffffe8, 28}, %% 8
{16#ffffea, 24}, %% 9 (TAB)
{16#3ffffffc, 30}, %% 10 (LF)
{16#fffffe9, 28}, %% 11
{16#fffffea, 28}, %% 12
{16#3ffffffd, 30}, %% 13 (CR)
{16#fffffeb, 28}, %% 14
{16#fffffec, 28}, %% 15
%% 16-31 (more control characters)
{16#fffffed, 28}, %% 16
{16#fffffee, 28}, %% 17
{16#fffffef, 28}, %% 18
{16#ffffff0, 28}, %% 19
{16#ffffff1, 28}, %% 20
{16#ffffff2, 28}, %% 21
{16#3ffffffe, 30}, %% 22
{16#ffffff3, 28}, %% 23
{16#ffffff4, 28}, %% 24
{16#ffffff5, 28}, %% 25
{16#ffffff6, 28}, %% 26
{16#ffffff7, 28}, %% 27
{16#ffffff8, 28}, %% 28
{16#ffffff9, 28}, %% 29
{16#ffffffa, 28}, %% 30
{16#ffffffb, 28}, %% 31
%% 32-47 (printable ASCII start)
{16#14, 6}, %% 32 ' '
{16#3f8, 10}, %% 33 '!'
{16#3f9, 10}, %% 34 '"'
{16#ffa, 12}, %% 35 '#'
{16#1ff9, 13}, %% 36 '$'
{16#15, 6}, %% 37 '%'
{16#f8, 8}, %% 38 '&'
{16#7fa, 11}, %% 39 '''
{16#3fa, 10}, %% 40 '('
{16#3fb, 10}, %% 41 ')'
{16#f9, 8}, %% 42 '*'
{16#7fb, 11}, %% 43 '+'
{16#fa, 8}, %% 44 ','
{16#16, 6}, %% 45 '-'
{16#17, 6}, %% 46 '.'
{16#18, 6}, %% 47 '/'
%% 48-63 (digits and some symbols)
{16#0, 5}, %% 48 '0'
{16#1, 5}, %% 49 '1'
{16#2, 5}, %% 50 '2'
{16#19, 6}, %% 51 '3'
{16#1a, 6}, %% 52 '4'
{16#1b, 6}, %% 53 '5'
{16#1c, 6}, %% 54 '6'
{16#1d, 6}, %% 55 '7'
{16#1e, 6}, %% 56 '8'
{16#1f, 6}, %% 57 '9'
{16#5c, 7}, %% 58 ':'
{16#fb, 8}, %% 59 ';'
{16#7ffc, 15}, %% 60 '<'
{16#20, 6}, %% 61 '='
{16#ffb, 12}, %% 62 '>'
{16#3fc, 10}, %% 63 '?'
%% 64-79 (uppercase letters start)
{16#1ffa, 13}, %% 64 '@'
{16#21, 6}, %% 65 'A'
{16#5d, 7}, %% 66 'B'
{16#5e, 7}, %% 67 'C'
{16#5f, 7}, %% 68 'D'
{16#60, 7}, %% 69 'E'
{16#61, 7}, %% 70 'F'
{16#62, 7}, %% 71 'G'
{16#63, 7}, %% 72 'H'
{16#64, 7}, %% 73 'I'
{16#65, 7}, %% 74 'J'
{16#66, 7}, %% 75 'K'
{16#67, 7}, %% 76 'L'
{16#68, 7}, %% 77 'M'
{16#69, 7}, %% 78 'N'
{16#6a, 7}, %% 79 'O'
%% 80-95 (uppercase letters continue)
{16#6b, 7}, %% 80 'P'
{16#6c, 7}, %% 81 'Q'
{16#6d, 7}, %% 82 'R'
{16#6e, 7}, %% 83 'S'
{16#6f, 7}, %% 84 'T'
{16#70, 7}, %% 85 'U'
{16#71, 7}, %% 86 'V'
{16#72, 7}, %% 87 'W'
{16#fc, 8}, %% 88 'X'
{16#73, 7}, %% 89 'Y'
{16#fd, 8}, %% 90 'Z'
{16#1ffb, 13}, %% 91 '['
{16#7fff0, 19}, %% 92 '\'
{16#1ffc, 13}, %% 93 ']'
{16#3ffc, 14}, %% 94 '^'
{16#22, 6}, %% 95 '_'
%% 96-111 (lowercase letters start)
{16#7ffd, 15}, %% 96 '`'
{16#3, 5}, %% 97 'a'
{16#23, 6}, %% 98 'b'
{16#4, 5}, %% 99 'c'
{16#24, 6}, %% 100 'd'
{16#5, 5}, %% 101 'e'
{16#25, 6}, %% 102 'f'
{16#26, 6}, %% 103 'g'
{16#27, 6}, %% 104 'h'
{16#6, 5}, %% 105 'i'
{16#74, 7}, %% 106 'j'
{16#75, 7}, %% 107 'k'
{16#28, 6}, %% 108 'l'
{16#29, 6}, %% 109 'm'
{16#2a, 6}, %% 110 'n'
{16#7, 5}, %% 111 'o'
%% 112-127 (lowercase letters continue)
{16#2b, 6}, %% 112 'p'
{16#76, 7}, %% 113 'q'
{16#2c, 6}, %% 114 'r'
{16#8, 5}, %% 115 's'
{16#9, 5}, %% 116 't'
{16#2d, 6}, %% 117 'u'
{16#77, 7}, %% 118 'v'
{16#78, 7}, %% 119 'w'
{16#79, 7}, %% 120 'x'
{16#7a, 7}, %% 121 'y'
{16#7b, 7}, %% 122 'z'
{16#7ffe, 15}, %% 123 '{'
{16#7fc, 11}, %% 124 '|'
{16#3ffd, 14}, %% 125 '}'
{16#1ffd, 13}, %% 126 '~'
{16#ffffffc, 28}, %% 127 (DEL)
%% 128-143 (extended ASCII)
{16#fffe6, 20}, %% 128
{16#3fffd2, 22}, %% 129
{16#fffe7, 20}, %% 130
{16#fffe8, 20}, %% 131
{16#3fffd3, 22}, %% 132
{16#3fffd4, 22}, %% 133
{16#3fffd5, 22}, %% 134
{16#7fffd9, 23}, %% 135
{16#3fffd6, 22}, %% 136
{16#7fffda, 23}, %% 137
{16#7fffdb, 23}, %% 138
{16#7fffdc, 23}, %% 139
{16#7fffdd, 23}, %% 140
{16#7fffde, 23}, %% 141
{16#ffffeb, 24}, %% 142
{16#7fffdf, 23}, %% 143
%% 144-159
{16#ffffec, 24}, %% 144
{16#ffffed, 24}, %% 145
{16#3fffd7, 22}, %% 146
{16#7fffe0, 23}, %% 147
{16#ffffee, 24}, %% 148
{16#7fffe1, 23}, %% 149
{16#7fffe2, 23}, %% 150
{16#7fffe3, 23}, %% 151
{16#7fffe4, 23}, %% 152
{16#1fffdc, 21}, %% 153
{16#3fffd8, 22}, %% 154
{16#7fffe5, 23}, %% 155
{16#3fffd9, 22}, %% 156
{16#7fffe6, 23}, %% 157
{16#7fffe7, 23}, %% 158
{16#ffffef, 24}, %% 159
%% 160-175
{16#3fffda, 22}, %% 160
{16#1fffdd, 21}, %% 161
{16#fffe9, 20}, %% 162
{16#3fffdb, 22}, %% 163
{16#3fffdc, 22}, %% 164
{16#7fffe8, 23}, %% 165
{16#7fffe9, 23}, %% 166
{16#1fffde, 21}, %% 167
{16#7fffea, 23}, %% 168
{16#3fffdd, 22}, %% 169
{16#3fffde, 22}, %% 170
{16#fffff0, 24}, %% 171
{16#1fffdf, 21}, %% 172
{16#3fffdf, 22}, %% 173
{16#7fffeb, 23}, %% 174
{16#7fffec, 23}, %% 175
%% 176-191
{16#1fffe0, 21}, %% 176
{16#1fffe1, 21}, %% 177
{16#3fffe0, 22}, %% 178
{16#1fffe2, 21}, %% 179
{16#7fffed, 23}, %% 180
{16#3fffe1, 22}, %% 181
{16#7fffee, 23}, %% 182
{16#7fffef, 23}, %% 183
{16#fffea, 20}, %% 184
{16#3fffe2, 22}, %% 185
{16#3fffe3, 22}, %% 186
{16#3fffe4, 22}, %% 187
{16#7ffff0, 23}, %% 188
{16#3fffe5, 22}, %% 189
{16#3fffe6, 22}, %% 190
{16#7ffff1, 23}, %% 191
%% 192-207
{16#3ffffe0, 26}, %% 192
{16#3ffffe1, 26}, %% 193
{16#fffeb, 20}, %% 194
{16#7fff1, 19}, %% 195
{16#3fffe7, 22}, %% 196
{16#7ffff2, 23}, %% 197
{16#3fffe8, 22}, %% 198
{16#1ffffec, 25}, %% 199
{16#3ffffe2, 26}, %% 200
{16#3ffffe3, 26}, %% 201
{16#3ffffe4, 26}, %% 202
{16#7ffffde, 27}, %% 203
{16#7ffffdf, 27}, %% 204
{16#3ffffe5, 26}, %% 205
{16#fffff1, 24}, %% 206
{16#1ffffed, 25}, %% 207
%% 208-223
{16#7fff2, 19}, %% 208
{16#1fffe3, 21}, %% 209
{16#3ffffe6, 26}, %% 210
{16#7ffffe0, 27}, %% 211
{16#7ffffe1, 27}, %% 212
{16#3ffffe7, 26}, %% 213
{16#7ffffe2, 27}, %% 214
{16#fffff2, 24}, %% 215
{16#1fffe4, 21}, %% 216
{16#1fffe5, 21}, %% 217
{16#3ffffe8, 26}, %% 218
{16#3ffffe9, 26}, %% 219
{16#ffffffd, 28}, %% 220
{16#7ffffe3, 27}, %% 221
{16#7ffffe4, 27}, %% 222
{16#7ffffe5, 27}, %% 223
%% 224-239
{16#fffec, 20}, %% 224
{16#fffff3, 24}, %% 225
{16#fffed, 20}, %% 226
{16#1fffe6, 21}, %% 227
{16#3fffe9, 22}, %% 228
{16#1fffe7, 21}, %% 229
{16#1fffe8, 21}, %% 230
{16#7ffff3, 23}, %% 231
{16#3fffea, 22}, %% 232
{16#3fffeb, 22}, %% 233
{16#1ffffee, 25}, %% 234
{16#1ffffef, 25}, %% 235
{16#fffff4, 24}, %% 236
{16#fffff5, 24}, %% 237
{16#3ffffea, 26}, %% 238
{16#7ffff4, 23}, %% 239
%% 240-255
{16#3ffffeb, 26}, %% 240
{16#7ffffe6, 27}, %% 241
{16#3ffffec, 26}, %% 242
{16#3ffffed, 26}, %% 243
{16#7ffffe7, 27}, %% 244
{16#7ffffe8, 27}, %% 245
{16#7ffffe9, 27}, %% 246
{16#7ffffea, 27}, %% 247
{16#7ffffeb, 27}, %% 248
{16#ffffffe, 28}, %% 249
{16#7ffffec, 27}, %% 250
{16#7ffffed, 27}, %% 251
{16#7ffffee, 27}, %% 252
{16#7ffffef, 27}, %% 253
{16#7fffff0, 27}, %% 254
{16#3ffffee, 26} %% 255
}).
%% EOS symbol (256) used for padding: code = 0x3fffffff, len = 30
-define(HUFFMAN_EOS_CODE, 16#3fffffff).
-define(HUFFMAN_EOS_BITS, 30).
%% Pre-encoded common header values for O(1) access
%% These are the Huffman-encoded forms of common values
%% Common methods (pre-encoded with huffman)
-define(HUFFMAN_GET, <<16#c1>>). %% "GET" huffman encoded
-define(HUFFMAN_POST, <<16#e1, 16#bf>>). %% "POST" huffman encoded
%% Common status codes (pre-encoded with huffman)
-define(HUFFMAN_200, <<16#08>>). %% "200" huffman encoded
-define(HUFFMAN_204, <<16#09, 16#a2>>). %% "204" huffman encoded
-define(HUFFMAN_206, <<16#09, 16#c2>>). %% "206" huffman encoded
-define(HUFFMAN_304, <<16#1a, 16#62>>). %% "304" huffman encoded
-define(HUFFMAN_400, <<16#4c, 16#08>>). %% "400" huffman encoded
-define(HUFFMAN_404, <<16#4c, 16#62>>). %% "404" huffman encoded
-define(HUFFMAN_500, <<16#a2, 16#08>>). %% "500" huffman encoded
%% Macro to get huffman code for a byte value (0-255)
%% Returns {Code, BitLength}
-define(HUFFMAN_CODE(Byte), element(Byte + 1, ?HUFFMAN_ENCODE_TABLE)).