media/libjpeg/jdhuff.h

   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  * 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 /* 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
  28 typedef struct {
  29   /* Basic tables: (element [0] of each array is unused) */
  30   INT32 maxcode[18];            /* largest code of length k (-1 if none) */
  31   /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
  32   INT32 valoffset[18];          /* huffval[] offset for codes of length k */
  33   /* 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    */
  37
  38   /* Link to public Huffman table (needed only in jpeg_huff_decode) */
  39   JHUFF_TBL *pub;
  40
  41   /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
  42    * the input data stream.  If the next Huffman code is no more
  43    * than HUFF_LOOKAHEAD bits long, we can obtain its length and
  44    * 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.
  50    */
  51   int lookup[1<<HUFF_LOOKAHEAD];
  52 } d_derived_tbl;
  53
  54 /* Expand a Huffman table definition into the derived format */
  55 EXTERN(void) jpeg_make_d_derived_tbl
  56         JPP((j_decompress_ptr cinfo, boolean isDC, int tblno,
  57              d_derived_tbl ** pdtbl));
  58
  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
  78 #if __WORDSIZE == 64 || defined(_WIN64)
  79
  80 typedef size_t bit_buf_type;    /* type of bit-extraction buffer */
  81 #define BIT_BUF_SIZE  64                /* size of buffer in bits */
  82
  83 #else
  84
  85 typedef INT32 bit_buf_type;     /* type of bit-extraction buffer */
  86 #define BIT_BUF_SIZE  32                /* size of buffer in bits */
  87
  88 #endif
  89
  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
  92  * 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)
  94  * because not all machines measure sizeof in 8-bit bytes.
  95  */
  96
  97 typedef 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 */
 100 } bitread_perm_state;
 101
 102 typedef struct {                /* Bitreading working state within an MCU */
 103   /* Current data source location */
 104   /* We need a copy, rather than munging the original, in case of suspension */
 105   const JOCTET * next_input_byte; /* => next byte to read from source */
 106   size_t bytes_in_buffer;       /* # of bytes remaining in source buffer */
 107   /* Bit input buffer --- note these values are kept in register variables,
 108    * 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 */
 112   /* Pointer needed by jpeg_fill_bit_buffer. */
 113   j_decompress_ptr cinfo;       /* back link to decompress master record */
 114 } 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; \
 126         get_buffer = permstate.get_buffer; \
 127         bits_left = permstate.bits_left;
 128
 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; \
 132         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 */
 169 EXTERN(boolean) jpeg_fill_bit_buffer
 170         JPP((bitread_working_state * state, register bit_buf_type get_buffer,
 171              register int bits_left, int nbits));
 172
 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); \
 201   if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
 202     DROP_BITS(nb); \
 203     result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
 204   } else { \
 205 slowlabel: \
 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
 212 #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
 232 /* Out-of-line case for Huffman code fetching */
 233 EXTERN(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));