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  * libjpeg-turbo Modifications:
   7  * Copyright (C) 2010-2011, 2015-2016, 2021, D. R. Commander.
   8  * Copyright (C) 2018, Matthias Räncker.
   9  * For conditions of distribution and use, see the accompanying README.ijg
  10  * file.
  11  *
  12  * This file contains declarations for Huffman entropy decoding routines
  13  * that are shared between the sequential decoder (jdhuff.c) and the
  14  * progressive decoder (jdphuff.c).  No other modules need to see these.
  15  */
  16
  17 #include "jconfigint.h"
  18
  19
  20 /* Derived data constructed for each Huffman table */
  21
  22 #define HUFF_LOOKAHEAD  8       /* # of bits of lookahead */
  23
  24 typedef struct {
  25   /* Basic tables: (element [0] of each array is unused) */
  26   JLONG maxcode[18];            /* largest code of length k (-1 if none) */
  27   /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
  28   JLONG valoffset[18];          /* huffval[] offset for codes of length k */
  29   /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
  30    * the smallest code of length k; so given a code of length k, the
  31    * corresponding symbol is huffval[code + valoffset[k]]
  32    */
  33
  34   /* Link to public Huffman table (needed only in jpeg_huff_decode) */
  35   JHUFF_TBL *pub;
  36
  37   /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of
  38    * the input data stream.  If the next Huffman code is no more
  39    * than HUFF_LOOKAHEAD bits long, we can obtain its length and
  40    * the corresponding symbol directly from this tables.
  41    *
  42    * The lower 8 bits of each table entry contain the number of
  43    * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1
  44    * if too long.  The next 8 bits of each entry contain the
  45    * symbol.
  46    */
  47   int lookup[1 << HUFF_LOOKAHEAD];
  48 } d_derived_tbl;
  49
  50 /* Expand a Huffman table definition into the derived format */
  51 EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC,
  52                                      int tblno, 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 #if !defined(_WIN32) && !defined(SIZEOF_SIZE_T)
  74 #error Cannot determine word size
  75 #endif
  76
  77 #if SIZEOF_SIZE_T == 8 || defined(_WIN64)
  78
  79 typedef size_t bit_buf_type;            /* type of bit-extraction buffer */
  80 #define BIT_BUF_SIZE  64                /* size of buffer in bits */
  81
  82 #elif defined(__x86_64__) && defined(__ILP32__)
  83
  84 typedef unsigned long long bit_buf_type; /* type of bit-extraction buffer */
  85 #define BIT_BUF_SIZE  64                 /* size of buffer in bits */
  86
  87 #else
  88
  89 typedef unsigned long bit_buf_type;     /* type of bit-extraction buffer */
  90 #define BIT_BUF_SIZE  32                /* size of buffer in bits */
  91
  92 #endif
  93
  94 /* If long is > 32 bits on your machine, and shifting/masking longs is
  95  * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
  96  * appropriately should be a win.  Unfortunately we can't define the size
  97  * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
  98  * because not all machines measure sizeof in 8-bit bytes.
  99  */
 100
 101 typedef struct {                /* Bitreading state saved across MCUs */
 102   bit_buf_type get_buffer;      /* current bit-extraction buffer */
 103   int bits_left;                /* # of unused bits in it */
 104 } bitread_perm_state;
 105
 106 typedef struct {                /* Bitreading working state within an MCU */
 107   /* Current data source location */
 108   /* We need a copy, rather than munging the original, in case of suspension */
 109   const JOCTET *next_input_byte; /* => next byte to read from source */
 110   size_t bytes_in_buffer;       /* # of bytes remaining in source buffer */
 111   /* Bit input buffer --- note these values are kept in register variables,
 112    * not in this struct, inside the inner loops.
 113    */
 114   bit_buf_type get_buffer;      /* current bit-extraction buffer */
 115   int bits_left;                /* # of unused bits in it */
 116   /* Pointer needed by jpeg_fill_bit_buffer. */
 117   j_decompress_ptr cinfo;       /* back link to decompress master record */
 118 } bitread_working_state;
 119
 120 /* Macros to declare and load/save bitread local variables. */
 121 #define BITREAD_STATE_VARS \
 122   register bit_buf_type get_buffer; \
 123   register int bits_left; \
 124   bitread_working_state br_state
 125
 126 #define BITREAD_LOAD_STATE(cinfop, permstate) \
 127   br_state.cinfo = cinfop; \
 128   br_state.next_input_byte = cinfop->src->next_input_byte; \
 129   br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
 130   get_buffer = permstate.get_buffer; \
 131   bits_left = permstate.bits_left;
 132
 133 #define BITREAD_SAVE_STATE(cinfop, permstate) \
 134   cinfop->src->next_input_byte = br_state.next_input_byte; \
 135   cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
 136   permstate.get_buffer = get_buffer; \
 137   permstate.bits_left = bits_left
 138
 139 /*
 140  * These macros provide the in-line portion of bit fetching.
 141  * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
 142  * before using GET_BITS, PEEK_BITS, or DROP_BITS.
 143  * The variables get_buffer and bits_left are assumed to be locals,
 144  * but the state struct might not be (jpeg_huff_decode needs this).
 145  *      CHECK_BIT_BUFFER(state, n, action);
 146  *              Ensure there are N bits in get_buffer; if suspend, take action.
 147  *      val = GET_BITS(n);
 148  *              Fetch next N bits.
 149  *      val = PEEK_BITS(n);
 150  *              Fetch next N bits without removing them from the buffer.
 151  *      DROP_BITS(n);
 152  *              Discard next N bits.
 153  * The value N should be a simple variable, not an expression, because it
 154  * is evaluated multiple times.
 155  */
 156
 157 #define CHECK_BIT_BUFFER(state, nbits, action) { \
 158   if (bits_left < (nbits)) { \
 159     if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \
 160       { action; } \
 161     get_buffer = (state).get_buffer;  bits_left = (state).bits_left; \
 162   } \
 163 }
 164
 165 #define GET_BITS(nbits) \
 166   (((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1))
 167
 168 #define PEEK_BITS(nbits) \
 169   (((int)(get_buffer >> (bits_left -  (nbits)))) & ((1 << (nbits)) - 1))
 170
 171 #define DROP_BITS(nbits) \
 172   (bits_left -= (nbits))
 173
 174 /* Load up the bit buffer to a depth of at least nbits */
 175 EXTERN(boolean) jpeg_fill_bit_buffer(bitread_working_state *state,
 176                                      register bit_buf_type get_buffer,
 177                                      register int bits_left, int nbits);
 178
 179
 180 /*
 181  * Code for extracting next Huffman-coded symbol from input bit stream.
 182  * Again, this is time-critical and we make the main paths be macros.
 183  *
 184  * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
 185  * without looping.  Usually, more than 95% of the Huffman codes will be 8
 186  * or fewer bits long.  The few overlength codes are handled with a loop,
 187  * which need not be inline code.
 188  *
 189  * Notes about the HUFF_DECODE macro:
 190  * 1. Near the end of the data segment, we may fail to get enough bits
 191  *    for a lookahead.  In that case, we do it the hard way.
 192  * 2. If the lookahead table contains no entry, the next code must be
 193  *    more than HUFF_LOOKAHEAD bits long.
 194  * 3. jpeg_huff_decode returns -1 if forced to suspend.
 195  */
 196
 197 #define HUFF_DECODE(result, state, htbl, failaction, slowlabel) { \
 198   register int nb, look; \
 199   if (bits_left < HUFF_LOOKAHEAD) { \
 200     if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \
 201       { failaction; } \
 202     get_buffer = state.get_buffer;  bits_left = state.bits_left; \
 203     if (bits_left < HUFF_LOOKAHEAD) { \
 204       nb = 1;  goto slowlabel; \
 205     } \
 206   } \
 207   look = PEEK_BITS(HUFF_LOOKAHEAD); \
 208   if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \
 209     DROP_BITS(nb); \
 210     result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \
 211   } else { \
 212 slowlabel: \
 213     if ((result = \
 214          jpeg_huff_decode(&state, get_buffer, bits_left, htbl, nb)) < 0) \
 215       { failaction; } \
 216     get_buffer = state.get_buffer;  bits_left = state.bits_left; \
 217   } \
 218 }
 219
 220 #define HUFF_DECODE_FAST(s, nb, htbl) \
 221   FILL_BIT_BUFFER_FAST; \
 222   s = PEEK_BITS(HUFF_LOOKAHEAD); \
 223   s = htbl->lookup[s]; \
 224   nb = s >> HUFF_LOOKAHEAD; \
 225   /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \
 226   DROP_BITS(nb); \
 227   s = s & ((1 << HUFF_LOOKAHEAD) - 1); \
 228   if (nb > HUFF_LOOKAHEAD) { \
 229     /* Equivalent of jpeg_huff_decode() */ \
 230     /* Don't use GET_BITS() here because we don't want to modify bits_left */ \
 231     s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \
 232     while (s > htbl->maxcode[nb]) { \
 233       s <<= 1; \
 234       s |= GET_BITS(1); \
 235       nb++; \
 236     } \
 237     if (nb > 16) \
 238       s = 0; \
 239     else \
 240       s = htbl->pub->huffval[(int)(s + htbl->valoffset[nb]) & 0xFF]; \
 241   }
 242
 243 /* Out-of-line case for Huffman code fetching */
 244 EXTERN(int) jpeg_huff_decode(bitread_working_state *state,
 245                              register bit_buf_type get_buffer,
 246                              register int bits_left, d_derived_tbl *htbl,
 247                              int min_bits);