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