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, D. R. Commander.
8 * 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
16/* Derived data constructed for each Huffman table */
17
18#define HUFF_LOOKAHEAD  8       /* # of bits of lookahead */
19
20typedef struct {
21  /* Basic tables: (element [0] of each array is unused) */
22  INT32 maxcode[18];            /* largest code of length k (-1 if none) */
23  /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
24  INT32 valoffset[18];          /* huffval[] offset for codes of length k */
25  /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
26   * the smallest code of length k; so given a code of length k, the
27   * corresponding symbol is huffval[code + valoffset[k]]
28   */
29
30  /* Link to public Huffman table (needed only in jpeg_huff_decode) */
31  JHUFF_TBL *pub;
32
33  /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
34   * the input data stream.  If the next Huffman code is no more
35   * than HUFF_LOOKAHEAD bits long, we can obtain its length and
36   * the corresponding symbol directly from this tables.
37   *
38   * The lower 8 bits of each table entry contain the number of
39   * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
40   * if too long.  The next 8 bits of each entry contain the
41   * symbol.
42   */
43  int lookup[1<<HUFF_LOOKAHEAD];
44} d_derived_tbl;
45
46/* Expand a Huffman table definition into the derived format */
47EXTERN(void) jpeg_make_d_derived_tbl
48        (j_decompress_ptr cinfo, boolean isDC, int tblno,
49         d_derived_tbl ** pdtbl);
50
51
52/*
53 * Fetching the next N bits from the input stream is a time-critical operation
54 * for the Huffman decoders.  We implement it with a combination of inline
55 * macros and out-of-line subroutines.  Note that N (the number of bits
56 * demanded at one time) never exceeds 15 for JPEG use.
57 *
58 * We read source bytes into get_buffer and dole out bits as needed.
59 * If get_buffer already contains enough bits, they are fetched in-line
60 * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough
61 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
62 * as full as possible (not just to the number of bits needed; this
63 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
64 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
65 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
66 * at least the requested number of bits --- dummy zeroes are inserted if
67 * necessary.
68 */
69
70#if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
71#error Cannot determine word size
72#endif
73
74#if SIZEOF_SIZE_T==8 || defined(_WIN64)
75
76typedef size_t bit_buf_type;    /* type of bit-extraction buffer */
77#define BIT_BUF_SIZE  64                /* size of buffer in bits */
78
79#else
80
81typedef INT32 bit_buf_type;     /* type of bit-extraction buffer */
82#define BIT_BUF_SIZE  32                /* size of buffer in bits */
83
84#endif
85
86/* If long is > 32 bits on your machine, and shifting/masking longs is
87 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
88 * appropriately should be a win.  Unfortunately we can't define the size
89 * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
90 * because not all machines measure sizeof in 8-bit bytes.
91 */
92
93typedef struct {                /* Bitreading state saved across MCUs */
94  bit_buf_type get_buffer;      /* current bit-extraction buffer */
95  int bits_left;                /* # of unused bits in it */
96} bitread_perm_state;
97
98typedef struct {                /* Bitreading working state within an MCU */
99  /* Current data source location */
100  /* We need a copy, rather than munging the original, in case of suspension */
101  const JOCTET * next_input_byte; /* => next byte to read from source */
102  size_t bytes_in_buffer;       /* # of bytes remaining in source buffer */
103  /* Bit input buffer --- note these values are kept in register variables,
104   * not in this struct, inside the inner loops.
105   */
106  bit_buf_type get_buffer;      /* current bit-extraction buffer */
107  int bits_left;                /* # of unused bits in it */
108  /* Pointer needed by jpeg_fill_bit_buffer. */
109  j_decompress_ptr cinfo;       /* back link to decompress master record */
110} bitread_working_state;
111
112/* Macros to declare and load/save bitread local variables. */
113#define BITREAD_STATE_VARS  \
114        register bit_buf_type get_buffer;  \
115        register int bits_left;  \
116        bitread_working_state br_state
117
118#define BITREAD_LOAD_STATE(cinfop,permstate)  \
119        br_state.cinfo = cinfop; \
120        br_state.next_input_byte = cinfop->src->next_input_byte; \
121        br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
122        get_buffer = permstate.get_buffer; \
123        bits_left = permstate.bits_left;
124
125#define BITREAD_SAVE_STATE(cinfop,permstate)  \
126        cinfop->src->next_input_byte = br_state.next_input_byte; \
127        cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
128        permstate.get_buffer = get_buffer; \
129        permstate.bits_left = bits_left
130
131/*
132 * These macros provide the in-line portion of bit fetching.
133 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
134 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
135 * The variables get_buffer and bits_left are assumed to be locals,
136 * but the state struct might not be (jpeg_huff_decode needs this).
137 *      CHECK_BIT_BUFFER(state,n,action);
138 *              Ensure there are N bits in get_buffer; if suspend, take action.
139 *      val = GET_BITS(n);
140 *              Fetch next N bits.
141 *      val = PEEK_BITS(n);
142 *              Fetch next N bits without removing them from the buffer.
143 *      DROP_BITS(n);
144 *              Discard next N bits.
145 * The value N should be a simple variable, not an expression, because it
146 * is evaluated multiple times.
147 */
148
149#define CHECK_BIT_BUFFER(state,nbits,action) \
150        { if (bits_left < (nbits)) {  \
151            if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits))  \
152              { action; }  \
153            get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
154
155#define GET_BITS(nbits) \
156        (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1))
157
158#define PEEK_BITS(nbits) \
159        (((int) (get_buffer >> (bits_left -  (nbits)))) & ((1<<(nbits))-1))
160
161#define DROP_BITS(nbits) \
162        (bits_left -= (nbits))
163
164/* Load up the bit buffer to a depth of at least nbits */
165EXTERN(boolean) jpeg_fill_bit_buffer
166        (bitread_working_state * state, register bit_buf_type get_buffer,
167         register int bits_left, int nbits);
168
169
170/*
171 * Code for extracting next Huffman-coded symbol from input bit stream.
172 * Again, this is time-critical and we make the main paths be macros.
173 *
174 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
175 * without looping.  Usually, more than 95% of the Huffman codes will be 8
176 * or fewer bits long.  The few overlength codes are handled with a loop,
177 * which need not be inline code.
178 *
179 * Notes about the HUFF_DECODE macro:
180 * 1. Near the end of the data segment, we may fail to get enough bits
181 *    for a lookahead.  In that case, we do it the hard way.
182 * 2. If the lookahead table contains no entry, the next code must be
183 *    more than HUFF_LOOKAHEAD bits long.
184 * 3. jpeg_huff_decode returns -1 if forced to suspend.
185 */
186
187#define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
188{ register int nb, look; \
189  if (bits_left < HUFF_LOOKAHEAD) { \
190    if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
191    get_buffer = state.get_buffer; bits_left = state.bits_left; \
192    if (bits_left < HUFF_LOOKAHEAD) { \
193      nb = 1; goto slowlabel; \
194    } \
195  } \
196  look = PEEK_BITS(HUFF_LOOKAHEAD); \
197  if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
198    DROP_BITS(nb); \
199    result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
200  } else { \
201slowlabel: \
202    if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
203        { failaction; } \
204    get_buffer = state.get_buffer; bits_left = state.bits_left; \
205  } \
206}
207
208#define HUFF_DECODE_FAST(s,nb,htbl) \
209  FILL_BIT_BUFFER_FAST; \
210  s = PEEK_BITS(HUFF_LOOKAHEAD); \
211  s = htbl->lookup[s]; \
212  nb = s >> HUFF_LOOKAHEAD; \
213  /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
214  DROP_BITS(nb); \
215  s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
216  if (nb > HUFF_LOOKAHEAD) { \
217    /* Equivalent of jpeg_huff_decode() */ \
218    /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
219    s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
220    while (s > htbl->maxcode[nb]) { \
221      s <<= 1; \
222      s |= GET_BITS(1); \
223      nb++; \
224    } \
225    s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \
226  }
227
228/* Out-of-line case for Huffman code fetching */
229EXTERN(int) jpeg_huff_decode
230        (bitread_working_state * state, register bit_buf_type get_buffer,
231         register int bits_left, d_derived_tbl * htbl, int min_bits);
232