OFFIS DCMTK  Version 3.6.0
jdhuff16.h
1 /*
2  * jdhuff.h
3  *
4  * Copyright (C) 1991-1998, Thomas G. Lane.
5  * This file is part of the Independent JPEG Group's software.
6  * For conditions of distribution and use, see the accompanying README file.
7  *
8  * This file contains declarations for Huffman entropy decoding routines
9  * that are shared between the sequential decoder (jdhuff.c), the
10  * progressive decoder (jdphuff.c) and the lossless decoder (jdlhuff.c).
11  * No other modules need to see these.
12  */
13 
14 /* Short forms of external names for systems with brain-damaged linkers. */
15 
16 #ifdef NEED_SHORT_EXTERNAL_NAMES
17 #define jpeg_make_d_derived_tbl jpeg16_make_d_derived_tbl
18 #define jpeg_fill_bit_buffer jpeg16_fill_bit_buffer
19 #define jpeg_huff_decode jpeg16_huff_decode
20 #endif /* NEED_SHORT_EXTERNAL_NAMES */
21 
22 
23 /* Derived data constructed for each Huffman table */
24 
25 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */
26 
27 typedef struct {
28  /* Basic tables: (element [0] of each array is unused) */
29  IJG_INT32 maxcode[18]; /* largest code of length k (-1 if none) */
30  /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
31  IJG_INT32 valoffset[17]; /* huffval[] offset for codes of length k */
32  /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
33  * the smallest code of length k; so given a code of length k, the
34  * corresponding symbol is huffval[code + valoffset[k]]
35  */
36 
37  /* Link to public Huffman table (needed only in jpeg_huff_decode) */
38  JHUFF_TBL *pub;
39 
40  /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of
41  * the input data stream. If the next Huffman code is no more
42  * than HUFF_LOOKAHEAD bits long, we can obtain its length and
43  * the corresponding symbol directly from these tables.
44  */
45  int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
46  UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
48 
49 /* Expand a Huffman table definition into the derived format */
50 EXTERN(void) jpeg_make_d_derived_tbl
51  JPP((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 typedef IJG_INT32 bit_buf_type; /* type of bit-extraction buffer */
74 #define BIT_BUF_SIZE 32 /* size of buffer in bits */
75 
76 /* If long is > 32 bits on your machine, and shifting/masking longs is
77  * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
78  * appropriately should be a win. Unfortunately we can't define the size
79  * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
80  * because not all machines measure sizeof in 8-bit bytes.
81  */
82 
83 typedef struct { /* Bitreading state saved across MCUs */
84  bit_buf_type get_buffer; /* current bit-extraction buffer */
85  int bits_left; /* # of unused bits in it */
87 
88 typedef struct { /* Bitreading working state within an MCU */
89  /* Current data source location */
90  /* We need a copy, rather than munging the original, in case of suspension */
91  const JOCTET * next_input_byte; /* => next byte to read from source */
92  size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
93  /* Bit input buffer --- note these values are kept in register variables,
94  * not in this struct, inside the inner loops.
95  */
96  bit_buf_type get_buffer; /* current bit-extraction buffer */
97  int bits_left; /* # of unused bits in it */
98  /* Pointer needed by jpeg_fill_bit_buffer. */
99  j_decompress_ptr cinfo; /* back link to decompress master record */
101 
102 /* Macros to declare and load/save bitread local variables. */
103 #define BITREAD_STATE_VARS \
104  register bit_buf_type get_buffer; \
105  register int bits_left; \
106  bitread_working_state br_state
107 
108 #define BITREAD_LOAD_STATE(cinfop,permstate) \
109  br_state.cinfo = cinfop; \
110  br_state.next_input_byte = cinfop->src->next_input_byte; \
111  br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
112  get_buffer = permstate.get_buffer; \
113  bits_left = permstate.bits_left;
114 
115 #define BITREAD_SAVE_STATE(cinfop,permstate) \
116  cinfop->src->next_input_byte = br_state.next_input_byte; \
117  cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
118  permstate.get_buffer = get_buffer; \
119  permstate.bits_left = bits_left
120 
121 /*
122  * These macros provide the in-line portion of bit fetching.
123  * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
124  * before using GET_BITS, PEEK_BITS, or DROP_BITS.
125  * The variables get_buffer and bits_left are assumed to be locals,
126  * but the state struct might not be (jpeg_huff_decode needs this).
127  * CHECK_BIT_BUFFER(state,n,action);
128  * Ensure there are N bits in get_buffer; if suspend, take action.
129  * val = GET_BITS(n);
130  * Fetch next N bits.
131  * val = PEEK_BITS(n);
132  * Fetch next N bits without removing them from the buffer.
133  * DROP_BITS(n);
134  * Discard next N bits.
135  * The value N should be a simple variable, not an expression, because it
136  * is evaluated multiple times.
137  */
138 
139 #define CHECK_BIT_BUFFER(state,nbits,action) \
140  { if (bits_left < (nbits)) { \
141  if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \
142  { action; } \
143  get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
144 
145 #define GET_BITS(nbits) \
146  (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))
147 
148 #define PEEK_BITS(nbits) \
149  (((int) (get_buffer >> (bits_left - (nbits)))) & ((1<<(nbits))-1))
150 
151 #define DROP_BITS(nbits) \
152  (bits_left -= (nbits))
153 
154 /* Load up the bit buffer to a depth of at least nbits */
155 EXTERN(boolean) jpeg_fill_bit_buffer
156  JPP((bitread_working_state * state, register bit_buf_type get_buffer,
157  register int bits_left, int nbits));
158 
159 
160 /*
161  * Code for extracting next Huffman-coded symbol from input bit stream.
162  * Again, this is time-critical and we make the main paths be macros.
163  *
164  * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
165  * without looping. Usually, more than 950f the Huffman codes will be 8
166  * or fewer bits long. The few overlength codes are handled with a loop,
167  * which need not be inline code.
168  *
169  * Notes about the HUFF_DECODE macro:
170  * 1. Near the end of the data segment, we may fail to get enough bits
171  * for a lookahead. In that case, we do it the hard way.
172  * 2. If the lookahead table contains no entry, the next code must be
173  * more than HUFF_LOOKAHEAD bits long.
174  * 3. jpeg_huff_decode returns -1 if forced to suspend.
175  */
176 
177 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
178 { register int nb, look; \
179  if (bits_left < HUFF_LOOKAHEAD) { \
180  if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
181  get_buffer = state.get_buffer; bits_left = state.bits_left; \
182  if (bits_left < HUFF_LOOKAHEAD) { \
183  nb = 1; goto slowlabel; \
184  } \
185  } \
186  look = PEEK_BITS(HUFF_LOOKAHEAD); \
187  if ((nb = htbl->look_nbits[look]) != 0) { \
188  DROP_BITS(nb); \
189  result = htbl->look_sym[look]; \
190  } else { \
191  nb = HUFF_LOOKAHEAD+1; \
192 slowlabel: \
193  if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
194  { failaction; } \
195  get_buffer = state.get_buffer; bits_left = state.bits_left; \
196  } \
197 }
198 
199 /* Out-of-line case for Huffman code fetching */
200 EXTERN(int) jpeg_huff_decode
201  JPP((bitread_working_state * state, register bit_buf_type get_buffer,
202  register int bits_left, d_derived_tbl * htbl, int min_bits));
203 
204 
205 /* Common fields between sequential, progressive and lossless Huffman entropy
206  * decoder master structs.
207  */
208 
209 #define huffd_common_fields \
210  boolean insufficient_data; /* set TRUE after emmitting warning */ \
211  /* These fields are loaded into local variables at start of each MCU. \
212  * In case of suspension, we exit WITHOUT updating them. \
213  */ \
214  bitread_perm_state bitstate /* Bit buffer at start of MCU */
215 
216 /* Routines that are to be used by any or all of the entropy decoders are
217  * declared to receive a pointer to this structure. There are no actual
218  * instances of huffd_common_struct, only of shuff_entropy_decoder,
219  * phuff_entropy_decoder and lhuff_entropy_decoder.
220  */
221 struct huffd_common_struct {
222  huffd_common_fields; /* Fields common to all decoder struct types */
223  /* Additional fields follow in an actual shuff_entropy_decoder,
224  * phuff_entropy_decoder or lhuff_entropy_decoder struct. All four structs
225  * must agree on these initial fields! (This would be a lot cleaner in C++.)
226  */
227 };
228 
229 typedef struct huffd_common_struct * huffd_common_ptr;


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