1/*
2 * jdhuff.h
3 *
4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1991-1997, Thomas G. Lane.
6 * libjpeg-turbo Modifications:
7 * Copyright (C) 2010-2011, 2015-2016, 2021, D. R. Commander.
8 * Copyright (C) 2018, Matthias Räncker.
9 * For conditions of distribution and use, see the accompanying README.ijg
10 * file.
11 *
12 * This file contains declarations for Huffman entropy decoding routines
13 * that are shared between the sequential decoder (jdhuff.c) and the
14 * progressive decoder (jdphuff.c). No other modules need to see these.
15 */
16
17#include "jconfigint.h"
18
19
20/* Derived data constructed for each Huffman table */
21
22#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */
23
24typedef struct {
25 /* Basic tables: (element [0] of each array is unused) */
26 JLONG maxcode[18]; /* largest code of length k (-1 if none) */
27 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
28 JLONG valoffset[18]; /* huffval[] offset for codes of length k */
29 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
30 * the smallest code of length k; so given a code of length k, the
31 * corresponding symbol is huffval[code + valoffset[k]]
32 */
33
34 /* Link to public Huffman table (needed only in jpeg_huff_decode) */
35 JHUFF_TBL *pub;
36
37 /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
38 * the input data stream. If the next Huffman code is no more
39 * than HUFF_LOOKAHEAD bits long, we can obtain its length and
40 * the corresponding symbol directly from this tables.
41 *
42 * The lower 8 bits of each table entry contain the number of
43 * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
44 * if too long. The next 8 bits of each entry contain the
45 * symbol.
46 */
47 int lookup[1 << HUFF_LOOKAHEAD];
48} d_derived_tbl;
49
50/* Expand a Huffman table definition into the derived format */
51EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC,
52 int tblno, d_derived_tbl **pdtbl);
53
54
55/*
56 * Fetching the next N bits from the input stream is a time-critical operation
57 * for the Huffman decoders. We implement it with a combination of inline
58 * macros and out-of-line subroutines. Note that N (the number of bits
59 * demanded at one time) never exceeds 15 for JPEG use.
60 *
61 * We read source bytes into get_buffer and dole out bits as needed.
62 * If get_buffer already contains enough bits, they are fetched in-line
63 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough
64 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
65 * as full as possible (not just to the number of bits needed; this
66 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
67 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
68 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
69 * at least the requested number of bits --- dummy zeroes are inserted if
70 * necessary.
71 */
72
73#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
74#error Cannot determine word size
75#endif
76
77#if SIZEOF_SIZE_T == 8 || defined(_WIN64)
78
79typedef size_t bit_buf_type; /* type of bit-extraction buffer */
80#define BIT_BUF_SIZE 64 /* size of buffer in bits */
81
82#elif defined(__x86_64__) && defined(__ILP32__)
83
84typedef unsigned long long bit_buf_type; /* type of bit-extraction buffer */
85#define BIT_BUF_SIZE 64 /* size of buffer in bits */
86
87#else
88
89typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */
90#define BIT_BUF_SIZE 32 /* size of buffer in bits */
91
92#endif
93
94/* If long is > 32 bits on your machine, and shifting/masking longs is
95 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
96 * appropriately should be a win. Unfortunately we can't define the size
97 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
98 * because not all machines measure sizeof in 8-bit bytes.
99 */
100
101typedef struct { /* Bitreading state saved across MCUs */
102 bit_buf_type get_buffer; /* current bit-extraction buffer */
103 int bits_left; /* # of unused bits in it */
104} bitread_perm_state;
105
106typedef struct { /* Bitreading working state within an MCU */
107 /* Current data source location */
108 /* We need a copy, rather than munging the original, in case of suspension */
109 const JOCTET *next_input_byte; /* => next byte to read from source */
110 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
111 /* Bit input buffer --- note these values are kept in register variables,
112 * not in this struct, inside the inner loops.
113 */
114 bit_buf_type get_buffer; /* current bit-extraction buffer */
115 int bits_left; /* # of unused bits in it */
116 /* Pointer needed by jpeg_fill_bit_buffer. */
117 j_decompress_ptr cinfo; /* back link to decompress master record */
118} bitread_working_state;
119
120/* Macros to declare and load/save bitread local variables. */
121#define BITREAD_STATE_VARS \
122 register bit_buf_type get_buffer; \
123 register int bits_left; \
124 bitread_working_state br_state
125
126#define BITREAD_LOAD_STATE(cinfop, permstate) \
127 br_state.cinfo = cinfop; \
128 br_state.next_input_byte = cinfop->src->next_input_byte; \
129 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
130 get_buffer = permstate.get_buffer; \
131 bits_left = permstate.bits_left;
132
133#define BITREAD_SAVE_STATE(cinfop, permstate) \
134 cinfop->src->next_input_byte = br_state.next_input_byte; \
135 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
136 permstate.get_buffer = get_buffer; \
137 permstate.bits_left = bits_left
138
139/*
140 * These macros provide the in-line portion of bit fetching.
141 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
142 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
143 * The variables get_buffer and bits_left are assumed to be locals,
144 * but the state struct might not be (jpeg_huff_decode needs this).
145 * CHECK_BIT_BUFFER(state, n, action);
146 * Ensure there are N bits in get_buffer; if suspend, take action.
147 * val = GET_BITS(n);
148 * Fetch next N bits.
149 * val = PEEK_BITS(n);
150 * Fetch next N bits without removing them from the buffer.
151 * DROP_BITS(n);
152 * Discard next N bits.
153 * The value N should be a simple variable, not an expression, because it
154 * is evaluated multiple times.
155 */
156
157#define CHECK_BIT_BUFFER(state, nbits, action) { \
158 if (bits_left < (nbits)) { \
159 if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \
160 { action; } \
161 get_buffer = (state).get_buffer; bits_left = (state).bits_left; \
162 } \
163}
164
165#define GET_BITS(nbits) \
166 (((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1))
167
168#define PEEK_BITS(nbits) \
169 (((int)(get_buffer >> (bits_left - (nbits)))) & ((1 << (nbits)) - 1))
170
171#define DROP_BITS(nbits) \
172 (bits_left -= (nbits))
173
174/* Load up the bit buffer to a depth of at least nbits */
175EXTERN(boolean) jpeg_fill_bit_buffer(bitread_working_state *state,
176 register bit_buf_type get_buffer,
177 register int bits_left, int nbits);
178
179
180/*
181 * Code for extracting next Huffman-coded symbol from input bit stream.
182 * Again, this is time-critical and we make the main paths be macros.
183 *
184 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
185 * without looping. Usually, more than 95% of the Huffman codes will be 8
186 * or fewer bits long. The few overlength codes are handled with a loop,
187 * which need not be inline code.
188 *
189 * Notes about the HUFF_DECODE macro:
190 * 1. Near the end of the data segment, we may fail to get enough bits
191 * for a lookahead. In that case, we do it the hard way.
192 * 2. If the lookahead table contains no entry, the next code must be
193 * more than HUFF_LOOKAHEAD bits long.
194 * 3. jpeg_huff_decode returns -1 if forced to suspend.
195 */
196
197#define HUFF_DECODE(result, state, htbl, failaction, slowlabel) { \
198 register int nb, look; \
199 if (bits_left < HUFF_LOOKAHEAD) { \
200 if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \
201 { failaction; } \
202 get_buffer = state.get_buffer; bits_left = state.bits_left; \
203 if (bits_left < HUFF_LOOKAHEAD) { \
204 nb = 1; goto slowlabel; \
205 } \
206 } \
207 look = PEEK_BITS(HUFF_LOOKAHEAD); \
208 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
209 DROP_BITS(nb); \
210 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
211 } else { \
212slowlabel: \
213 if ((result = \
214 jpeg_huff_decode(&state, get_buffer, bits_left, htbl, nb)) < 0) \
215 { failaction; } \
216 get_buffer = state.get_buffer; bits_left = state.bits_left; \
217 } \
218}
219
220#define HUFF_DECODE_FAST(s, nb, htbl) \
221 FILL_BIT_BUFFER_FAST; \
222 s = PEEK_BITS(HUFF_LOOKAHEAD); \
223 s = htbl->lookup[s]; \
224 nb = s >> HUFF_LOOKAHEAD; \
225 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
226 DROP_BITS(nb); \
227 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
228 if (nb > HUFF_LOOKAHEAD) { \
229 /* Equivalent of jpeg_huff_decode() */ \
230 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
231 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
232 while (s > htbl->maxcode[nb]) { \
233 s <<= 1; \
234 s |= GET_BITS(1); \
235 nb++; \
236 } \
237 if (nb > 16) \
238 s = 0; \
239 else \
240 s = htbl->pub->huffval[(int)(s + htbl->valoffset[nb]) & 0xFF]; \
241 }
242
243/* Out-of-line case for Huffman code fetching */
244EXTERN(int) jpeg_huff_decode(bitread_working_state *state,
245 register bit_buf_type get_buffer,
246 register int bits_left, d_derived_tbl *htbl,
247 int min_bits);
248