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Thomas G. Lanebc79e061995-08-02 00:00:00 +00001/*
2 * jdhuff.h
3 *
DRCa73e8702012-12-31 02:52:30 +00004 * This file was part of the Independent JPEG Group's software:
Thomas G. Lane5ead57a1998-03-27 00:00:00 +00005 * Copyright (C) 1991-1997, Thomas G. Lane.
DRCa73e8702012-12-31 02:52:30 +00006 * Modifications:
DRCbc515802011-04-18 06:52:07 +00007 * Copyright (C) 2010-2011, D. R. Commander.
Thomas G. Lanebc79e061995-08-02 00:00:00 +00008 * For conditions of distribution and use, see the accompanying README file.
9 *
10 * This file contains declarations for Huffman entropy decoding routines
11 * that are shared between the sequential decoder (jdhuff.c) and the
12 * progressive decoder (jdphuff.c). No other modules need to see these.
13 */
14
15/* Short forms of external names for systems with brain-damaged linkers. */
16
17#ifdef NEED_SHORT_EXTERNAL_NAMES
18#define jpeg_make_d_derived_tbl jMkDDerived
19#define jpeg_fill_bit_buffer jFilBitBuf
20#define jpeg_huff_decode jHufDecode
21#endif /* NEED_SHORT_EXTERNAL_NAMES */
22
23
24/* Derived data constructed for each Huffman table */
25
26#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */
27
28typedef struct {
29 /* Basic tables: (element [0] of each array is unused) */
Thomas G. Lanebc79e061995-08-02 00:00:00 +000030 INT32 maxcode[18]; /* largest code of length k (-1 if none) */
31 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
DRC0fbb28e2010-07-30 17:15:52 +000032 INT32 valoffset[18]; /* huffval[] offset for codes of length k */
Thomas G. Lane5ead57a1998-03-27 00:00:00 +000033 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
34 * the smallest code of length k; so given a code of length k, the
35 * corresponding symbol is huffval[code + valoffset[k]]
36 */
Thomas G. Lanebc79e061995-08-02 00:00:00 +000037
38 /* Link to public Huffman table (needed only in jpeg_huff_decode) */
39 JHUFF_TBL *pub;
40
DRCe2816642009-09-28 00:33:02 +000041 /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
Thomas G. Lanebc79e061995-08-02 00:00:00 +000042 * the input data stream. If the next Huffman code is no more
43 * than HUFF_LOOKAHEAD bits long, we can obtain its length and
DRCe2816642009-09-28 00:33:02 +000044 * the corresponding symbol directly from this tables.
45 *
46 * The lower 8 bits of each table entry contain the number of
47 * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
48 * if too long. The next 8 bits of each entry contain the
49 * symbol.
Thomas G. Lanebc79e061995-08-02 00:00:00 +000050 */
DRCe2816642009-09-28 00:33:02 +000051 int lookup[1<<HUFF_LOOKAHEAD];
Thomas G. Lanebc79e061995-08-02 00:00:00 +000052} d_derived_tbl;
53
54/* Expand a Huffman table definition into the derived format */
Thomas G. Lane5ead57a1998-03-27 00:00:00 +000055EXTERN(void) jpeg_make_d_derived_tbl
56 JPP((j_decompress_ptr cinfo, boolean isDC, int tblno,
57 d_derived_tbl ** pdtbl));
Thomas G. Lanebc79e061995-08-02 00:00:00 +000058
59
60/*
61 * Fetching the next N bits from the input stream is a time-critical operation
62 * for the Huffman decoders. We implement it with a combination of inline
63 * macros and out-of-line subroutines. Note that N (the number of bits
64 * demanded at one time) never exceeds 15 for JPEG use.
65 *
66 * We read source bytes into get_buffer and dole out bits as needed.
67 * If get_buffer already contains enough bits, they are fetched in-line
68 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough
69 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
70 * as full as possible (not just to the number of bits needed; this
71 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
72 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
73 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
74 * at least the requested number of bits --- dummy zeroes are inserted if
75 * necessary.
76 */
77
DRC830d5fc2010-04-20 21:13:26 +000078#if __WORDSIZE == 64 || defined(_WIN64)
DRC021da082009-09-28 08:19:40 +000079
DRC04899092010-02-26 23:01:19 +000080typedef size_t bit_buf_type; /* type of bit-extraction buffer */
DRC021da082009-09-28 08:19:40 +000081#define BIT_BUF_SIZE 64 /* size of buffer in bits */
82
83#else
84
85typedef INT32 bit_buf_type; /* type of bit-extraction buffer */
86#define BIT_BUF_SIZE 32 /* size of buffer in bits */
87
88#endif
Thomas G. Lanebc79e061995-08-02 00:00:00 +000089
90/* If long is > 32 bits on your machine, and shifting/masking longs is
91 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
Thomas G. Lane5ead57a1998-03-27 00:00:00 +000092 * appropriately should be a win. Unfortunately we can't define the size
93 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
Thomas G. Lanebc79e061995-08-02 00:00:00 +000094 * because not all machines measure sizeof in 8-bit bytes.
95 */
96
97typedef struct { /* Bitreading state saved across MCUs */
98 bit_buf_type get_buffer; /* current bit-extraction buffer */
99 int bits_left; /* # of unused bits in it */
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000100} bitread_perm_state;
101
102typedef struct { /* Bitreading working state within an MCU */
Thomas G. Lane5ead57a1998-03-27 00:00:00 +0000103 /* Current data source location */
104 /* We need a copy, rather than munging the original, in case of suspension */
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000105 const JOCTET * next_input_byte; /* => next byte to read from source */
106 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
Thomas G. Lane5ead57a1998-03-27 00:00:00 +0000107 /* Bit input buffer --- note these values are kept in register variables,
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000108 * not in this struct, inside the inner loops.
109 */
110 bit_buf_type get_buffer; /* current bit-extraction buffer */
111 int bits_left; /* # of unused bits in it */
Thomas G. Lane5ead57a1998-03-27 00:00:00 +0000112 /* Pointer needed by jpeg_fill_bit_buffer. */
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000113 j_decompress_ptr cinfo; /* back link to decompress master record */
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000114} bitread_working_state;
115
116/* Macros to declare and load/save bitread local variables. */
117#define BITREAD_STATE_VARS \
118 register bit_buf_type get_buffer; \
119 register int bits_left; \
120 bitread_working_state br_state
121
122#define BITREAD_LOAD_STATE(cinfop,permstate) \
123 br_state.cinfo = cinfop; \
124 br_state.next_input_byte = cinfop->src->next_input_byte; \
125 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000126 get_buffer = permstate.get_buffer; \
Thomas G. Lane5ead57a1998-03-27 00:00:00 +0000127 bits_left = permstate.bits_left;
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000128
129#define BITREAD_SAVE_STATE(cinfop,permstate) \
130 cinfop->src->next_input_byte = br_state.next_input_byte; \
131 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000132 permstate.get_buffer = get_buffer; \
133 permstate.bits_left = bits_left
134
135/*
136 * These macros provide the in-line portion of bit fetching.
137 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
138 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
139 * The variables get_buffer and bits_left are assumed to be locals,
140 * but the state struct might not be (jpeg_huff_decode needs this).
141 * CHECK_BIT_BUFFER(state,n,action);
142 * Ensure there are N bits in get_buffer; if suspend, take action.
143 * val = GET_BITS(n);
144 * Fetch next N bits.
145 * val = PEEK_BITS(n);
146 * Fetch next N bits without removing them from the buffer.
147 * DROP_BITS(n);
148 * Discard next N bits.
149 * The value N should be a simple variable, not an expression, because it
150 * is evaluated multiple times.
151 */
152
153#define CHECK_BIT_BUFFER(state,nbits,action) \
154 { if (bits_left < (nbits)) { \
155 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \
156 { action; } \
157 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
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 */
Thomas G. Lane489583f1996-02-07 00:00:00 +0000169EXTERN(boolean) jpeg_fill_bit_buffer
170 JPP((bitread_working_state * state, register bit_buf_type get_buffer,
171 register int bits_left, int nbits));
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000172
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)) {failaction;} \
195 get_buffer = state.get_buffer; bits_left = state.bits_left; \
196 if (bits_left < HUFF_LOOKAHEAD) { \
197 nb = 1; goto slowlabel; \
198 } \
199 } \
200 look = PEEK_BITS(HUFF_LOOKAHEAD); \
DRCe2816642009-09-28 00:33:02 +0000201 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000202 DROP_BITS(nb); \
DRCe2816642009-09-28 00:33:02 +0000203 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000204 } else { \
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000205slowlabel: \
206 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
207 { failaction; } \
208 get_buffer = state.get_buffer; bits_left = state.bits_left; \
209 } \
210}
211
DRCbc515802011-04-18 06:52:07 +0000212#define HUFF_DECODE_FAST(s,nb,htbl) \
213 FILL_BIT_BUFFER_FAST; \
214 s = PEEK_BITS(HUFF_LOOKAHEAD); \
215 s = htbl->lookup[s]; \
216 nb = s >> HUFF_LOOKAHEAD; \
217 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
218 DROP_BITS(nb); \
219 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
220 if (nb > HUFF_LOOKAHEAD) { \
221 /* Equivalent of jpeg_huff_decode() */ \
222 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
223 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
224 while (s > htbl->maxcode[nb]) { \
225 s <<= 1; \
226 s |= GET_BITS(1); \
227 nb++; \
228 } \
229 s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \
230 }
231
Thomas G. Lanebc79e061995-08-02 00:00:00 +0000232/* Out-of-line case for Huffman code fetching */
Thomas G. Lane489583f1996-02-07 00:00:00 +0000233EXTERN(int) jpeg_huff_decode
234 JPP((bitread_working_state * state, register bit_buf_type get_buffer,
235 register int bits_left, d_derived_tbl * htbl, int min_bits));