source: golgotha/src/i4/loaders/jpg/jdhuff.h @ 80

Last change on this file since 80 was 80, checked in by Sam Hocevar, 12 years ago
  • Adding the Golgotha source code. Not sure what's going to be interesting in there, but since it's all public domain, there's certainly stuff to pick up.
  • Property svn:keywords set to Id
File size: 8.0 KB
Line 
1/*
2 * jdhuff.h
3 *
4 * Copyright (C) 1991-1996, 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) and the
10 * progressive decoder (jdphuff.c).  No other modules need to see these.
11 */
12
13/* Short forms of external names for systems with brain-damaged linkers. */
14
15#ifdef NEED_SHORT_EXTERNAL_NAMES
16#define jpeg_make_d_derived_tbl jMkDDerived
17#define jpeg_fill_bit_buffer    jFilBitBuf
18#define jpeg_huff_decode        jHufDecode
19#endif /* NEED_SHORT_EXTERNAL_NAMES */
20
21
22/* Derived data constructed for each Huffman table */
23
24#define HUFF_LOOKAHEAD  8       /* # of bits of lookahead */
25
26typedef struct {
27  /* Basic tables: (element [0] of each array is unused) */
28  INT32 mincode[17];            /* smallest code of length k */
29  INT32 maxcode[18];            /* largest code of length k (-1 if none) */
30  /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
31  int valptr[17];               /* huffval[] index of 1st symbol of length k */
32
33  /* Link to public Huffman table (needed only in jpeg_huff_decode) */
34  JHUFF_TBL *pub;
35
36  /* Lookahead tables: 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 these tables.
40   */
41  int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
42  UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
43} d_derived_tbl;
44
45/* Expand a Huffman table definition into the derived format */
46EXTERN(void) jpeg_make_d_derived_tbl JPP((j_decompress_ptr cinfo,
47                                JHUFF_TBL * htbl, d_derived_tbl ** pdtbl));
48
49
50/*
51 * Fetching the next N bits from the input stream is a time-critical operation
52 * for the Huffman decoders.  We implement it with a combination of inline
53 * macros and out-of-line subroutines.  Note that N (the number of bits
54 * demanded at one time) never exceeds 15 for JPEG use.
55 *
56 * We read source bytes into get_buffer and dole out bits as needed.
57 * If get_buffer already contains enough bits, they are fetched in-line
58 * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough
59 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
60 * as full as possible (not just to the number of bits needed; this
61 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
62 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
63 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
64 * at least the requested number of bits --- dummy zeroes are inserted if
65 * necessary.
66 */
67
68typedef INT32 bit_buf_type;     /* type of bit-extraction buffer */
69#define BIT_BUF_SIZE  32        /* size of buffer in bits */
70
71/* If long is > 32 bits on your machine, and shifting/masking longs is
72 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
73 * appropriately should be a win.  Unfortunately we can't do this with
74 * something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
75 * because not all machines measure sizeof in 8-bit bytes.
76 */
77
78typedef struct {                /* Bitreading state saved across MCUs */
79  bit_buf_type get_buffer;      /* current bit-extraction buffer */
80  int bits_left;                /* # of unused bits in it */
81  boolean printed_eod;          /* flag to suppress multiple warning msgs */
82} bitread_perm_state;
83
84typedef struct {                /* Bitreading working state within an MCU */
85  /* current data source state */
86  const JOCTET * next_input_byte; /* => next byte to read from source */
87  size_t bytes_in_buffer;       /* # of bytes remaining in source buffer */
88  int unread_marker;            /* nonzero if we have hit a marker */
89  /* bit input buffer --- note these values are kept in register variables,
90   * not in this struct, inside the inner loops.
91   */
92  bit_buf_type get_buffer;      /* current bit-extraction buffer */
93  int bits_left;                /* # of unused bits in it */
94  /* pointers needed by jpeg_fill_bit_buffer */
95  j_decompress_ptr cinfo;       /* back link to decompress master record */
96  boolean * printed_eod_ptr;    /* => flag in permanent state */
97} bitread_working_state;
98
99/* Macros to declare and load/save bitread local variables. */
100#define BITREAD_STATE_VARS  \
101        register bit_buf_type get_buffer;  \
102        register int bits_left;  \
103        bitread_working_state br_state
104
105#define BITREAD_LOAD_STATE(cinfop,permstate)  \
106        br_state.cinfo = cinfop; \
107        br_state.next_input_byte = cinfop->src->next_input_byte; \
108        br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
109        br_state.unread_marker = cinfop->unread_marker; \
110        get_buffer = permstate.get_buffer; \
111        bits_left = permstate.bits_left; \
112        br_state.printed_eod_ptr = & permstate.printed_eod
113
114#define BITREAD_SAVE_STATE(cinfop,permstate)  \
115        cinfop->src->next_input_byte = br_state.next_input_byte; \
116        cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
117        cinfop->unread_marker = br_state.unread_marker; \
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 */
155EXTERN(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 95% of 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; \
192slowlabel: \
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 */
200EXTERN(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));
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