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
51 (j_decompress_ptr cinfo, boolean isDC, int tblno,
52 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#else
83
84typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */
85#define BIT_BUF_SIZE 32 /* size of buffer in bits */
86
87#endif
88
89/* If long is > 32 bits on your machine, and shifting/masking longs is
90 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
91 * appropriately should be a win. Unfortunately we can't define the size
92 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
93 * because not all machines measure sizeof in 8-bit bytes.
94 */
95
96typedef struct { /* Bitreading state saved across MCUs */
97 bit_buf_type get_buffer; /* current bit-extraction buffer */
98 int bits_left; /* # of unused bits in it */
99} bitread_perm_state;
100
101typedef struct { /* Bitreading working state within an MCU */
102 /* Current data source location */
103 /* We need a copy, rather than munging the original, in case of suspension */
104 const JOCTET *next_input_byte; /* => next byte to read from source */
105 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
106 /* Bit input buffer --- note these values are kept in register variables,
107 * not in this struct, inside the inner loops.
108 */
109 bit_buf_type get_buffer; /* current bit-extraction buffer */
110 int bits_left; /* # of unused bits in it */
111 /* Pointer needed by jpeg_fill_bit_buffer. */
112 j_decompress_ptr cinfo; /* back link to decompress master record */
113} bitread_working_state;
114
115/* Macros to declare and load/save bitread local variables. */
116#define BITREAD_STATE_VARS \
117 register bit_buf_type get_buffer; \
118 register int bits_left; \
119 bitread_working_state br_state
120
121#define BITREAD_LOAD_STATE(cinfop,permstate) \
122 br_state.cinfo = cinfop; \
123 br_state.next_input_byte = cinfop->src->next_input_byte; \
124 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
125 get_buffer = permstate.get_buffer; \
126 bits_left = permstate.bits_left;
127
128#define BITREAD_SAVE_STATE(cinfop,permstate) \
129 cinfop->src->next_input_byte = br_state.next_input_byte; \
130 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
131 permstate.get_buffer = get_buffer; \
132 permstate.bits_left = bits_left
133
134/*
135 * These macros provide the in-line portion of bit fetching.
136 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
137 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
138 * The variables get_buffer and bits_left are assumed to be locals,
139 * but the state struct might not be (jpeg_huff_decode needs this).
140 * CHECK_BIT_BUFFER(state,n,action);
141 * Ensure there are N bits in get_buffer; if suspend, take action.
142 * val = GET_BITS(n);
143 * Fetch next N bits.
144 * val = PEEK_BITS(n);
145 * Fetch next N bits without removing them from the buffer.
146 * DROP_BITS(n);
147 * Discard next N bits.
148 * The value N should be a simple variable, not an expression, because it
149 * is evaluated multiple times.
150 */
151
152#define CHECK_BIT_BUFFER(state,nbits,action) \
153 { if (bits_left < (nbits)) { \
154 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \
155 { action; } \
156 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
157
158#define GET_BITS(nbits) \
159 (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))
160
161#define PEEK_BITS(nbits) \
162 (((int) (get_buffer >> (bits_left - (nbits)))) & ((1<<(nbits))-1))
163
164#define DROP_BITS(nbits) \
165 (bits_left -= (nbits))
166
167/* Load up the bit buffer to a depth of at least nbits */
168EXTERN(boolean) jpeg_fill_bit_buffer
169 (bitread_working_state *state, register bit_buf_type get_buffer,
170 register int bits_left, int nbits);
171
172
173/*
174 * Code for extracting next Huffman-coded symbol from input bit stream.
175 * Again, this is time-critical and we make the main paths be macros.
176 *
177 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
178 * without looping. Usually, more than 95% of the Huffman codes will be 8
179 * or fewer bits long. The few overlength codes are handled with a loop,
180 * which need not be inline code.
181 *
182 * Notes about the HUFF_DECODE macro:
183 * 1. Near the end of the data segment, we may fail to get enough bits
184 * for a lookahead. In that case, we do it the hard way.
185 * 2. If the lookahead table contains no entry, the next code must be
186 * more than HUFF_LOOKAHEAD bits long.
187 * 3. jpeg_huff_decode returns -1 if forced to suspend.
188 */
189
190#define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
191{ register int nb, look; \
192 if (bits_left < HUFF_LOOKAHEAD) { \
193 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
194 get_buffer = state.get_buffer; bits_left = state.bits_left; \
195 if (bits_left < HUFF_LOOKAHEAD) { \
196 nb = 1; goto slowlabel; \
197 } \
198 } \
199 look = PEEK_BITS(HUFF_LOOKAHEAD); \
200 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
201 DROP_BITS(nb); \
202 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
203 } else { \
204slowlabel: \
205 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
206 { failaction; } \
207 get_buffer = state.get_buffer; bits_left = state.bits_left; \
208 } \
209}
210
211#define HUFF_DECODE_FAST(s,nb,htbl,slowlabel) \
212 FILL_BIT_BUFFER_FAST; \
213 s = PEEK_BITS(HUFF_LOOKAHEAD); \
214 s = htbl->lookup[s]; \
215 nb = s >> HUFF_LOOKAHEAD; \
216 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
217 DROP_BITS(nb); \
218 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
219 if (nb > HUFF_LOOKAHEAD) { \
220 /* Equivalent of jpeg_huff_decode() */ \
221 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
222 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
223 while (s > htbl->maxcode[nb]) { \
224 s <<= 1; \
225 s |= GET_BITS(1); \
226 nb++; \
227 } \
228 if (nb > 16) \
229 goto slowlabel; \
230 s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) ]; \
231 }
232
233/* Out-of-line case for Huffman code fetching */
234EXTERN(int) jpeg_huff_decode
235 (bitread_working_state *state, register bit_buf_type get_buffer,
236 register int bits_left, d_derived_tbl *htbl, int min_bits);
237