root/3rdparty/libjpeg/jdhuff.c

/* [<][>][^][v][top][bottom][index][help] */

DEFINITIONS

This source file includes following definitions.
  1. LOCAL
  2. LOCAL
  3. LOCAL
  4. LOCAL
  5. METHODDEF
  6. METHODDEF
  7. METHODDEF
  8. METHODDEF
  9. METHODDEF
  10. METHODDEF
  11. METHODDEF
  12. GLOBAL

/*
 * jdhuff.c
 *
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * Modified 2006-2012 by Guido Vollbeding.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains Huffman entropy decoding routines.
 * Both sequential and progressive modes are supported in this single module.
 *
 * Much of the complexity here has to do with supporting input suspension.
 * If the data source module demands suspension, we want to be able to back
 * up to the start of the current MCU.  To do this, we copy state variables
 * into local working storage, and update them back to the permanent
 * storage only upon successful completion of an MCU.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* Derived data constructed for each Huffman table */

#define HUFF_LOOKAHEAD  8       /* # of bits of lookahead */

typedef struct {
  /* Basic tables: (element [0] of each array is unused) */
  INT32 maxcode[18];            /* largest code of length k (-1 if none) */
  /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
  INT32 valoffset[17];          /* huffval[] offset for codes of length k */
  /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
   * the smallest code of length k; so given a code of length k, the
   * corresponding symbol is huffval[code + valoffset[k]]
   */

  /* Link to public Huffman table (needed only in jpeg_huff_decode) */
  JHUFF_TBL *pub;

  /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of
   * the input data stream.  If the next Huffman code is no more
   * than HUFF_LOOKAHEAD bits long, we can obtain its length and
   * the corresponding symbol directly from these tables.
   */
  int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
  UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
} d_derived_tbl;


/*
 * Fetching the next N bits from the input stream is a time-critical operation
 * for the Huffman decoders.  We implement it with a combination of inline
 * macros and out-of-line subroutines.  Note that N (the number of bits
 * demanded at one time) never exceeds 15 for JPEG use.
 *
 * We read source bytes into get_buffer and dole out bits as needed.
 * If get_buffer already contains enough bits, they are fetched in-line
 * by the macros CHECK_BIT_BUFFER and GET_BITS.  When there aren't enough
 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
 * as full as possible (not just to the number of bits needed; this
 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
 * at least the requested number of bits --- dummy zeroes are inserted if
 * necessary.
 */

typedef INT32 bit_buf_type;     /* type of bit-extraction buffer */
#define BIT_BUF_SIZE  32        /* size of buffer in bits */

/* If long is > 32 bits on your machine, and shifting/masking longs is
 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
 * appropriately should be a win.  Unfortunately we can't define the size
 * with something like  #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
 * because not all machines measure sizeof in 8-bit bytes.
 */

typedef struct {                /* Bitreading state saved across MCUs */
  bit_buf_type get_buffer;      /* current bit-extraction buffer */
  int bits_left;                /* # of unused bits in it */
} bitread_perm_state;

typedef struct {                /* Bitreading working state within an MCU */
  /* Current data source location */
  /* We need a copy, rather than munging the original, in case of suspension */
  const JOCTET * next_input_byte; /* => next byte to read from source */
  size_t bytes_in_buffer;       /* # of bytes remaining in source buffer */
  /* Bit input buffer --- note these values are kept in register variables,
   * not in this struct, inside the inner loops.
   */
  bit_buf_type get_buffer;      /* current bit-extraction buffer */
  int bits_left;                /* # of unused bits in it */
  /* Pointer needed by jpeg_fill_bit_buffer. */
  j_decompress_ptr cinfo;       /* back link to decompress master record */
} bitread_working_state;

/* Macros to declare and load/save bitread local variables. */
#define BITREAD_STATE_VARS  \
        register bit_buf_type get_buffer;  \
        register int bits_left;  \
        bitread_working_state br_state

#define BITREAD_LOAD_STATE(cinfop,permstate)  \
        br_state.cinfo = cinfop; \
        br_state.next_input_byte = cinfop->src->next_input_byte; \
        br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
        get_buffer = permstate.get_buffer; \
        bits_left = permstate.bits_left;

#define BITREAD_SAVE_STATE(cinfop,permstate)  \
        cinfop->src->next_input_byte = br_state.next_input_byte; \
        cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
        permstate.get_buffer = get_buffer; \
        permstate.bits_left = bits_left

/*
 * These macros provide the in-line portion of bit fetching.
 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
 * The variables get_buffer and bits_left are assumed to be locals,
 * but the state struct might not be (jpeg_huff_decode needs this).
 *      CHECK_BIT_BUFFER(state,n,action);
 *              Ensure there are N bits in get_buffer; if suspend, take action.
 *      val = GET_BITS(n);
 *              Fetch next N bits.
 *      val = PEEK_BITS(n);
 *              Fetch next N bits without removing them from the buffer.
 *      DROP_BITS(n);
 *              Discard next N bits.
 * The value N should be a simple variable, not an expression, because it
 * is evaluated multiple times.
 */

#define CHECK_BIT_BUFFER(state,nbits,action) \
        { if (bits_left < (nbits)) {  \
            if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits))  \
              { action; }  \
            get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }

#define GET_BITS(nbits) \
        (((int) (get_buffer >> (bits_left -= (nbits)))) & BIT_MASK(nbits))

#define PEEK_BITS(nbits) \
        (((int) (get_buffer >> (bits_left -  (nbits)))) & BIT_MASK(nbits))

#define DROP_BITS(nbits) \
        (bits_left -= (nbits))


/*
 * Code for extracting next Huffman-coded symbol from input bit stream.
 * Again, this is time-critical and we make the main paths be macros.
 *
 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
 * without looping.  Usually, more than 95% of the Huffman codes will be 8
 * or fewer bits long.  The few overlength codes are handled with a loop,
 * which need not be inline code.
 *
 * Notes about the HUFF_DECODE macro:
 * 1. Near the end of the data segment, we may fail to get enough bits
 *    for a lookahead.  In that case, we do it the hard way.
 * 2. If the lookahead table contains no entry, the next code must be
 *    more than HUFF_LOOKAHEAD bits long.
 * 3. jpeg_huff_decode returns -1 if forced to suspend.
 */

#define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
{ register int nb, look; \
  if (bits_left < HUFF_LOOKAHEAD) { \
    if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
    get_buffer = state.get_buffer; bits_left = state.bits_left; \
    if (bits_left < HUFF_LOOKAHEAD) { \
      nb = 1; goto slowlabel; \
    } \
  } \
  look = PEEK_BITS(HUFF_LOOKAHEAD); \
  if ((nb = htbl->look_nbits[look]) != 0) { \
    DROP_BITS(nb); \
    result = htbl->look_sym[look]; \
  } else { \
    nb = HUFF_LOOKAHEAD+1; \
slowlabel: \
    if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
        { failaction; } \
    get_buffer = state.get_buffer; bits_left = state.bits_left; \
  } \
}


/*
 * Expanded entropy decoder object for Huffman decoding.
 *
 * The savable_state subrecord contains fields that change within an MCU,
 * but must not be updated permanently until we complete the MCU.
 */

typedef struct {
  unsigned int EOBRUN;                  /* remaining EOBs in EOBRUN */
  int last_dc_val[MAX_COMPS_IN_SCAN];   /* last DC coef for each component */
} savable_state;

/* This macro is to work around compilers with missing or broken
 * structure assignment.  You'll need to fix this code if you have
 * such a compiler and you change MAX_COMPS_IN_SCAN.
 */

#ifndef NO_STRUCT_ASSIGN
#define ASSIGN_STATE(dest,src)  ((dest) = (src))
#else
#if MAX_COMPS_IN_SCAN == 4
#define ASSIGN_STATE(dest,src)  \
        ((dest).EOBRUN = (src).EOBRUN, \
         (dest).last_dc_val[0] = (src).last_dc_val[0], \
         (dest).last_dc_val[1] = (src).last_dc_val[1], \
         (dest).last_dc_val[2] = (src).last_dc_val[2], \
         (dest).last_dc_val[3] = (src).last_dc_val[3])
#endif
#endif


typedef struct {
  struct jpeg_entropy_decoder pub; /* public fields */

  /* These fields are loaded into local variables at start of each MCU.
   * In case of suspension, we exit WITHOUT updating them.
   */
  bitread_perm_state bitstate;  /* Bit buffer at start of MCU */
  savable_state saved;          /* Other state at start of MCU */

  /* These fields are NOT loaded into local working state. */
  boolean insufficient_data;    /* set TRUE after emitting warning */
  unsigned int restarts_to_go;  /* MCUs left in this restart interval */

  /* Following two fields used only in progressive mode */

  /* Pointers to derived tables (these workspaces have image lifespan) */
  d_derived_tbl * derived_tbls[NUM_HUFF_TBLS];

  d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */

  /* Following fields used only in sequential mode */

  /* Pointers to derived tables (these workspaces have image lifespan) */
  d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
  d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];

  /* Precalculated info set up by start_pass for use in decode_mcu: */

  /* Pointers to derived tables to be used for each block within an MCU */
  d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
  d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
  /* Whether we care about the DC and AC coefficient values for each block */
  int coef_limit[D_MAX_BLOCKS_IN_MCU];
} huff_entropy_decoder;

typedef huff_entropy_decoder * huff_entropy_ptr;


static const int jpeg_zigzag_order[8][8] = {
  {  0,  1,  5,  6, 14, 15, 27, 28 },
  {  2,  4,  7, 13, 16, 26, 29, 42 },
  {  3,  8, 12, 17, 25, 30, 41, 43 },
  {  9, 11, 18, 24, 31, 40, 44, 53 },
  { 10, 19, 23, 32, 39, 45, 52, 54 },
  { 20, 22, 33, 38, 46, 51, 55, 60 },
  { 21, 34, 37, 47, 50, 56, 59, 61 },
  { 35, 36, 48, 49, 57, 58, 62, 63 }
};

static const int jpeg_zigzag_order7[7][7] = {
  {  0,  1,  5,  6, 14, 15, 27 },
  {  2,  4,  7, 13, 16, 26, 28 },
  {  3,  8, 12, 17, 25, 29, 38 },
  {  9, 11, 18, 24, 30, 37, 39 },
  { 10, 19, 23, 31, 36, 40, 45 },
  { 20, 22, 32, 35, 41, 44, 46 },
  { 21, 33, 34, 42, 43, 47, 48 }
};

static const int jpeg_zigzag_order6[6][6] = {
  {  0,  1,  5,  6, 14, 15 },
  {  2,  4,  7, 13, 16, 25 },
  {  3,  8, 12, 17, 24, 26 },
  {  9, 11, 18, 23, 27, 32 },
  { 10, 19, 22, 28, 31, 33 },
  { 20, 21, 29, 30, 34, 35 }
};

static const int jpeg_zigzag_order5[5][5] = {
  {  0,  1,  5,  6, 14 },
  {  2,  4,  7, 13, 15 },
  {  3,  8, 12, 16, 21 },
  {  9, 11, 17, 20, 22 },
  { 10, 18, 19, 23, 24 }
};

static const int jpeg_zigzag_order4[4][4] = {
  { 0,  1,  5,  6 },
  { 2,  4,  7, 12 },
  { 3,  8, 11, 13 },
  { 9, 10, 14, 15 }
};

static const int jpeg_zigzag_order3[3][3] = {
  { 0, 1, 5 },
  { 2, 4, 6 },
  { 3, 7, 8 }
};

static const int jpeg_zigzag_order2[2][2] = {
  { 0, 1 },
  { 2, 3 }
};


/*
 * Compute the derived values for a Huffman table.
 * This routine also performs some validation checks on the table.
 */

LOCAL(void)
jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
                         d_derived_tbl ** pdtbl)
{
  JHUFF_TBL *htbl;
  d_derived_tbl *dtbl;
  int p, i, l, si, numsymbols;
  int lookbits, ctr;
  char huffsize[257];
  unsigned int huffcode[257];
  unsigned int code;

  /* Note that huffsize[] and huffcode[] are filled in code-length order,
   * paralleling the order of the symbols themselves in htbl->huffval[].
   */

  /* Find the input Huffman table */
  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
  htbl =
    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
  if (htbl == NULL)
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);

  /* Allocate a workspace if we haven't already done so. */
  if (*pdtbl == NULL)
    *pdtbl = (d_derived_tbl *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                  SIZEOF(d_derived_tbl));
  dtbl = *pdtbl;
  dtbl->pub = htbl;             /* fill in back link */

  /* Figure C.1: make table of Huffman code length for each symbol */

  p = 0;
  for (l = 1; l <= 16; l++) {
    i = (int) htbl->bits[l];
    if (i < 0 || p + i > 256)   /* protect against table overrun */
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
    while (i--)
      huffsize[p++] = (char) l;
  }
  huffsize[p] = 0;
  numsymbols = p;

  /* Figure C.2: generate the codes themselves */
  /* We also validate that the counts represent a legal Huffman code tree. */

  code = 0;
  si = huffsize[0];
  p = 0;
  while (huffsize[p]) {
    while (((int) huffsize[p]) == si) {
      huffcode[p++] = code;
      code++;
    }
    /* code is now 1 more than the last code used for codelength si; but
     * it must still fit in si bits, since no code is allowed to be all ones.
     */
    if (((INT32) code) >= (((INT32) 1) << si))
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
    code <<= 1;
    si++;
  }

  /* Figure F.15: generate decoding tables for bit-sequential decoding */

  p = 0;
  for (l = 1; l <= 16; l++) {
    if (htbl->bits[l]) {
      /* valoffset[l] = huffval[] index of 1st symbol of code length l,
       * minus the minimum code of length l
       */
      dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
      p += htbl->bits[l];
      dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
    } else {
      dtbl->maxcode[l] = -1;    /* -1 if no codes of this length */
    }
  }
  dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */

  /* Compute lookahead tables to speed up decoding.
   * First we set all the table entries to 0, indicating "too long";
   * then we iterate through the Huffman codes that are short enough and
   * fill in all the entries that correspond to bit sequences starting
   * with that code.
   */

  MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));

  p = 0;
  for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
    for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
      /* l = current code's length, p = its index in huffcode[] & huffval[]. */
      /* Generate left-justified code followed by all possible bit sequences */
      lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
      for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
        dtbl->look_nbits[lookbits] = l;
        dtbl->look_sym[lookbits] = htbl->huffval[p];
        lookbits++;
      }
    }
  }

  /* Validate symbols as being reasonable.
   * For AC tables, we make no check, but accept all byte values 0..255.
   * For DC tables, we require the symbols to be in range 0..15.
   * (Tighter bounds could be applied depending on the data depth and mode,
   * but this is sufficient to ensure safe decoding.)
   */
  if (isDC) {
    for (i = 0; i < numsymbols; i++) {
      int sym = htbl->huffval[i];
      if (sym < 0 || sym > 15)
        ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
    }
  }
}


/*
 * Out-of-line code for bit fetching.
 * Note: current values of get_buffer and bits_left are passed as parameters,
 * but are returned in the corresponding fields of the state struct.
 *
 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
 * of get_buffer to be used.  (On machines with wider words, an even larger
 * buffer could be used.)  However, on some machines 32-bit shifts are
 * quite slow and take time proportional to the number of places shifted.
 * (This is true with most PC compilers, for instance.)  In this case it may
 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
 */

#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS  15        /* minimum allowable value */
#else
#define MIN_GET_BITS  (BIT_BUF_SIZE-7)
#endif


LOCAL(boolean)
jpeg_fill_bit_buffer (bitread_working_state * state,
                      register bit_buf_type get_buffer, register int bits_left,
                      int nbits)
/* Load up the bit buffer to a depth of at least nbits */
{
  /* Copy heavily used state fields into locals (hopefully registers) */
  register const JOCTET * next_input_byte = state->next_input_byte;
  register size_t bytes_in_buffer = state->bytes_in_buffer;
  j_decompress_ptr cinfo = state->cinfo;

  /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
  /* (It is assumed that no request will be for more than that many bits.) */
  /* We fail to do so only if we hit a marker or are forced to suspend. */

  if (cinfo->unread_marker == 0) {      /* cannot advance past a marker */
    while (bits_left < MIN_GET_BITS) {
      register int c;

      /* Attempt to read a byte */
      if (bytes_in_buffer == 0) {
        if (! (*cinfo->src->fill_input_buffer) (cinfo))
          return FALSE;
        next_input_byte = cinfo->src->next_input_byte;
        bytes_in_buffer = cinfo->src->bytes_in_buffer;
      }
      bytes_in_buffer--;
      c = GETJOCTET(*next_input_byte++);

      /* If it's 0xFF, check and discard stuffed zero byte */
      if (c == 0xFF) {
        /* Loop here to discard any padding FF's on terminating marker,
         * so that we can save a valid unread_marker value.  NOTE: we will
         * accept multiple FF's followed by a 0 as meaning a single FF data
         * byte.  This data pattern is not valid according to the standard.
         */
        do {
          if (bytes_in_buffer == 0) {
            if (! (*cinfo->src->fill_input_buffer) (cinfo))
              return FALSE;
            next_input_byte = cinfo->src->next_input_byte;
            bytes_in_buffer = cinfo->src->bytes_in_buffer;
          }
          bytes_in_buffer--;
          c = GETJOCTET(*next_input_byte++);
        } while (c == 0xFF);

        if (c == 0) {
          /* Found FF/00, which represents an FF data byte */
          c = 0xFF;
        } else {
          /* Oops, it's actually a marker indicating end of compressed data.
           * Save the marker code for later use.
           * Fine point: it might appear that we should save the marker into
           * bitread working state, not straight into permanent state.  But
           * once we have hit a marker, we cannot need to suspend within the
           * current MCU, because we will read no more bytes from the data
           * source.  So it is OK to update permanent state right away.
           */
          cinfo->unread_marker = c;
          /* See if we need to insert some fake zero bits. */
          goto no_more_bytes;
        }
      }

      /* OK, load c into get_buffer */
      get_buffer = (get_buffer << 8) | c;
      bits_left += 8;
    } /* end while */
  } else {
  no_more_bytes:
    /* We get here if we've read the marker that terminates the compressed
     * data segment.  There should be enough bits in the buffer register
     * to satisfy the request; if so, no problem.
     */
    if (nbits > bits_left) {
      /* Uh-oh.  Report corrupted data to user and stuff zeroes into
       * the data stream, so that we can produce some kind of image.
       * We use a nonvolatile flag to ensure that only one warning message
       * appears per data segment.
       */
      if (! ((huff_entropy_ptr) cinfo->entropy)->insufficient_data) {
        WARNMS(cinfo, JWRN_HIT_MARKER);
        ((huff_entropy_ptr) cinfo->entropy)->insufficient_data = TRUE;
      }
      /* Fill the buffer with zero bits */
      get_buffer <<= MIN_GET_BITS - bits_left;
      bits_left = MIN_GET_BITS;
    }
  }

  /* Unload the local registers */
  state->next_input_byte = next_input_byte;
  state->bytes_in_buffer = bytes_in_buffer;
  state->get_buffer = get_buffer;
  state->bits_left = bits_left;

  return TRUE;
}


/*
 * Figure F.12: extend sign bit.
 * On some machines, a shift and sub will be faster than a table lookup.
 */

#ifdef AVOID_TABLES

#define BIT_MASK(nbits)   ((1<<(nbits))-1)
#define HUFF_EXTEND(x,s)  ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x))

#else

#define BIT_MASK(nbits)   bmask[nbits]
#define HUFF_EXTEND(x,s)  ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x))

static const int bmask[16] =    /* bmask[n] is mask for n rightmost bits */
  { 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF,
    0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF };

#endif /* AVOID_TABLES */


/*
 * Out-of-line code for Huffman code decoding.
 */

LOCAL(int)
jpeg_huff_decode (bitread_working_state * state,
                  register bit_buf_type get_buffer, register int bits_left,
                  d_derived_tbl * htbl, int min_bits)
{
  register int l = min_bits;
  register INT32 code;

  /* HUFF_DECODE has determined that the code is at least min_bits */
  /* bits long, so fetch that many bits in one swoop. */

  CHECK_BIT_BUFFER(*state, l, return -1);
  code = GET_BITS(l);

  /* Collect the rest of the Huffman code one bit at a time. */
  /* This is per Figure F.16 in the JPEG spec. */

  while (code > htbl->maxcode[l]) {
    code <<= 1;
    CHECK_BIT_BUFFER(*state, 1, return -1);
    code |= GET_BITS(1);
    l++;
  }

  /* Unload the local registers */
  state->get_buffer = get_buffer;
  state->bits_left = bits_left;

  /* With garbage input we may reach the sentinel value l = 17. */

  if (l > 16) {
    WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
    return 0;                   /* fake a zero as the safest result */
  }

  return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
}


/*
 * Check for a restart marker & resynchronize decoder.
 * Returns FALSE if must suspend.
 */

LOCAL(boolean)
process_restart (j_decompress_ptr cinfo)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int ci;

  /* Throw away any unused bits remaining in bit buffer; */
  /* include any full bytes in next_marker's count of discarded bytes */
  cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
  entropy->bitstate.bits_left = 0;

  /* Advance past the RSTn marker */
  if (! (*cinfo->marker->read_restart_marker) (cinfo))
    return FALSE;

  /* Re-initialize DC predictions to 0 */
  for (ci = 0; ci < cinfo->comps_in_scan; ci++)
    entropy->saved.last_dc_val[ci] = 0;
  /* Re-init EOB run count, too */
  entropy->saved.EOBRUN = 0;

  /* Reset restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;

  /* Reset out-of-data flag, unless read_restart_marker left us smack up
   * against a marker.  In that case we will end up treating the next data
   * segment as empty, and we can avoid producing bogus output pixels by
   * leaving the flag set.
   */
  if (cinfo->unread_marker == 0)
    entropy->insufficient_data = FALSE;

  return TRUE;
}


/*
 * Huffman MCU decoding.
 * Each of these routines decodes and returns one MCU's worth of
 * Huffman-compressed coefficients.
 * The coefficients are reordered from zigzag order into natural array order,
 * but are not dequantized.
 *
 * The i'th block of the MCU is stored into the block pointed to by
 * MCU_data[i].  WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
 * (Wholesale zeroing is usually a little faster than retail...)
 *
 * We return FALSE if data source requested suspension.  In that case no
 * changes have been made to permanent state.  (Exception: some output
 * coefficients may already have been assigned.  This is harmless for
 * spectral selection, since we'll just re-assign them on the next call.
 * Successive approximation AC refinement has to be more careful, however.)
 */

/*
 * MCU decoding for DC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF(boolean)
decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int Al = cinfo->Al;
  register int s, r;
  int blkn, ci;
  JBLOCKROW block;
  BITREAD_STATE_VARS;
  savable_state state;
  d_derived_tbl * tbl;
  jpeg_component_info * compptr;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
        return FALSE;
  }

  /* If we've run out of data, just leave the MCU set to zeroes.
   * This way, we return uniform gray for the remainder of the segment.
   */
  if (! entropy->insufficient_data) {

    /* Load up working state */
    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(state, entropy->saved);

    /* Outer loop handles each block in the MCU */

    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      block = MCU_data[blkn];
      ci = cinfo->MCU_membership[blkn];
      compptr = cinfo->cur_comp_info[ci];
      tbl = entropy->derived_tbls[compptr->dc_tbl_no];

      /* Decode a single block's worth of coefficients */

      /* Section F.2.2.1: decode the DC coefficient difference */
      HUFF_DECODE(s, br_state, tbl, return FALSE, label1);
      if (s) {
        CHECK_BIT_BUFFER(br_state, s, return FALSE);
        r = GET_BITS(s);
        s = HUFF_EXTEND(r, s);
      }

      /* Convert DC difference to actual value, update last_dc_val */
      s += state.last_dc_val[ci];
      state.last_dc_val[ci] = s;
      /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */
      (*block)[0] = (JCOEF) (s << Al);
    }

    /* Completed MCU, so update state */
    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(entropy->saved, state);
  }

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * MCU decoding for AC initial scan (either spectral selection,
 * or first pass of successive approximation).
 */

METHODDEF(boolean)
decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  register int s, k, r;
  unsigned int EOBRUN;
  int Se, Al;
  const int * natural_order;
  JBLOCKROW block;
  BITREAD_STATE_VARS;
  d_derived_tbl * tbl;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
        return FALSE;
  }

  /* If we've run out of data, just leave the MCU set to zeroes.
   * This way, we return uniform gray for the remainder of the segment.
   */
  if (! entropy->insufficient_data) {

    Se = cinfo->Se;
    Al = cinfo->Al;
    natural_order = cinfo->natural_order;

    /* Load up working state.
     * We can avoid loading/saving bitread state if in an EOB run.
     */
    EOBRUN = entropy->saved.EOBRUN;     /* only part of saved state we need */

    /* There is always only one block per MCU */

    if (EOBRUN)                 /* if it's a band of zeroes... */
      EOBRUN--;                 /* ...process it now (we do nothing) */
    else {
      BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
      block = MCU_data[0];
      tbl = entropy->ac_derived_tbl;

      for (k = cinfo->Ss; k <= Se; k++) {
        HUFF_DECODE(s, br_state, tbl, return FALSE, label2);
        r = s >> 4;
        s &= 15;
        if (s) {
          k += r;
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          r = GET_BITS(s);
          s = HUFF_EXTEND(r, s);
          /* Scale and output coefficient in natural (dezigzagged) order */
          (*block)[natural_order[k]] = (JCOEF) (s << Al);
        } else {
          if (r != 15) {        /* EOBr, run length is 2^r + appended bits */
            if (r) {            /* EOBr, r > 0 */
              EOBRUN = 1 << r;
              CHECK_BIT_BUFFER(br_state, r, return FALSE);
              r = GET_BITS(r);
              EOBRUN += r;
              EOBRUN--;         /* this band is processed at this moment */
            }
            break;              /* force end-of-band */
          }
          k += 15;              /* ZRL: skip 15 zeroes in band */
        }
      }

      BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
    }

    /* Completed MCU, so update state */
    entropy->saved.EOBRUN = EOBRUN;     /* only part of saved state we need */
  }

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * MCU decoding for DC successive approximation refinement scan.
 * Note: we assume such scans can be multi-component, although the spec
 * is not very clear on the point.
 */

METHODDEF(boolean)
decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int p1 = 1 << cinfo->Al;      /* 1 in the bit position being coded */
  int blkn;
  JBLOCKROW block;
  BITREAD_STATE_VARS;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
        return FALSE;
  }

  /* Not worth the cycles to check insufficient_data here,
   * since we will not change the data anyway if we read zeroes.
   */

  /* Load up working state */
  BITREAD_LOAD_STATE(cinfo,entropy->bitstate);

  /* Outer loop handles each block in the MCU */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    block = MCU_data[blkn];

    /* Encoded data is simply the next bit of the two's-complement DC value */
    CHECK_BIT_BUFFER(br_state, 1, return FALSE);
    if (GET_BITS(1))
      (*block)[0] |= p1;
    /* Note: since we use |=, repeating the assignment later is safe */
  }

  /* Completed MCU, so update state */
  BITREAD_SAVE_STATE(cinfo,entropy->bitstate);

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * MCU decoding for AC successive approximation refinement scan.
 */

METHODDEF(boolean)
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  register int s, k, r;
  unsigned int EOBRUN;
  int Se, p1, m1;
  const int * natural_order;
  JBLOCKROW block;
  JCOEFPTR thiscoef;
  BITREAD_STATE_VARS;
  d_derived_tbl * tbl;
  int num_newnz;
  int newnz_pos[DCTSIZE2];

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
        return FALSE;
  }

  /* If we've run out of data, don't modify the MCU.
   */
  if (! entropy->insufficient_data) {

    Se = cinfo->Se;
    p1 = 1 << cinfo->Al;        /* 1 in the bit position being coded */
    m1 = (-1) << cinfo->Al;     /* -1 in the bit position being coded */
    natural_order = cinfo->natural_order;

    /* Load up working state */
    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
    EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */

    /* There is always only one block per MCU */
    block = MCU_data[0];
    tbl = entropy->ac_derived_tbl;

    /* If we are forced to suspend, we must undo the assignments to any newly
     * nonzero coefficients in the block, because otherwise we'd get confused
     * next time about which coefficients were already nonzero.
     * But we need not undo addition of bits to already-nonzero coefficients;
     * instead, we can test the current bit to see if we already did it.
     */
    num_newnz = 0;

    /* initialize coefficient loop counter to start of band */
    k = cinfo->Ss;

    if (EOBRUN == 0) {
      do {
        HUFF_DECODE(s, br_state, tbl, goto undoit, label3);
        r = s >> 4;
        s &= 15;
        if (s) {
          if (s != 1)           /* size of new coef should always be 1 */
            WARNMS(cinfo, JWRN_HUFF_BAD_CODE);
          CHECK_BIT_BUFFER(br_state, 1, goto undoit);
          if (GET_BITS(1))
            s = p1;             /* newly nonzero coef is positive */
          else
            s = m1;             /* newly nonzero coef is negative */
        } else {
          if (r != 15) {
            EOBRUN = 1 << r;    /* EOBr, run length is 2^r + appended bits */
            if (r) {
              CHECK_BIT_BUFFER(br_state, r, goto undoit);
              r = GET_BITS(r);
              EOBRUN += r;
            }
            break;              /* rest of block is handled by EOB logic */
          }
          /* note s = 0 for processing ZRL */
        }
        /* Advance over already-nonzero coefs and r still-zero coefs,
         * appending correction bits to the nonzeroes.  A correction bit is 1
         * if the absolute value of the coefficient must be increased.
         */
        do {
          thiscoef = *block + natural_order[k];
          if (*thiscoef) {
            CHECK_BIT_BUFFER(br_state, 1, goto undoit);
            if (GET_BITS(1)) {
              if ((*thiscoef & p1) == 0) { /* do nothing if already set it */
                if (*thiscoef >= 0)
                  *thiscoef += p1;
                else
                  *thiscoef += m1;
              }
            }
          } else {
            if (--r < 0)
              break;            /* reached target zero coefficient */
          }
          k++;
        } while (k <= Se);
        if (s) {
          int pos = natural_order[k];
          /* Output newly nonzero coefficient */
          (*block)[pos] = (JCOEF) s;
          /* Remember its position in case we have to suspend */
          newnz_pos[num_newnz++] = pos;
        }
        k++;
      } while (k <= Se);
    }

    if (EOBRUN) {
      /* Scan any remaining coefficient positions after the end-of-band
       * (the last newly nonzero coefficient, if any).  Append a correction
       * bit to each already-nonzero coefficient.  A correction bit is 1
       * if the absolute value of the coefficient must be increased.
       */
      do {
        thiscoef = *block + natural_order[k];
        if (*thiscoef) {
          CHECK_BIT_BUFFER(br_state, 1, goto undoit);
          if (GET_BITS(1)) {
            if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */
              if (*thiscoef >= 0)
                *thiscoef += p1;
              else
                *thiscoef += m1;
            }
          }
        }
        k++;
      } while (k <= Se);
      /* Count one block completed in EOB run */
      EOBRUN--;
    }

    /* Completed MCU, so update state */
    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
    entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */
  }

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;

undoit:
  /* Re-zero any output coefficients that we made newly nonzero */
  while (num_newnz)
    (*block)[newnz_pos[--num_newnz]] = 0;

  return FALSE;
}


/*
 * Decode one MCU's worth of Huffman-compressed coefficients,
 * partial blocks.
 */

METHODDEF(boolean)
decode_mcu_sub (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  const int * natural_order;
  int Se, blkn;
  BITREAD_STATE_VARS;
  savable_state state;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
        return FALSE;
  }

  /* If we've run out of data, just leave the MCU set to zeroes.
   * This way, we return uniform gray for the remainder of the segment.
   */
  if (! entropy->insufficient_data) {

    natural_order = cinfo->natural_order;
    Se = cinfo->lim_Se;

    /* Load up working state */
    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(state, entropy->saved);

    /* Outer loop handles each block in the MCU */

    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      JBLOCKROW block = MCU_data[blkn];
      d_derived_tbl * htbl;
      register int s, k, r;
      int coef_limit, ci;

      /* Decode a single block's worth of coefficients */

      /* Section F.2.2.1: decode the DC coefficient difference */
      htbl = entropy->dc_cur_tbls[blkn];
      HUFF_DECODE(s, br_state, htbl, return FALSE, label1);

      htbl = entropy->ac_cur_tbls[blkn];
      k = 1;
      coef_limit = entropy->coef_limit[blkn];
      if (coef_limit) {
        /* Convert DC difference to actual value, update last_dc_val */
        if (s) {
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          r = GET_BITS(s);
          s = HUFF_EXTEND(r, s);
        }
        ci = cinfo->MCU_membership[blkn];
        s += state.last_dc_val[ci];
        state.last_dc_val[ci] = s;
        /* Output the DC coefficient */
        (*block)[0] = (JCOEF) s;

        /* Section F.2.2.2: decode the AC coefficients */
        /* Since zeroes are skipped, output area must be cleared beforehand */
        for (; k < coef_limit; k++) {
          HUFF_DECODE(s, br_state, htbl, return FALSE, label2);

          r = s >> 4;
          s &= 15;

          if (s) {
            k += r;
            CHECK_BIT_BUFFER(br_state, s, return FALSE);
            r = GET_BITS(s);
            s = HUFF_EXTEND(r, s);
            /* Output coefficient in natural (dezigzagged) order.
             * Note: the extra entries in natural_order[] will save us
             * if k > Se, which could happen if the data is corrupted.
             */
            (*block)[natural_order[k]] = (JCOEF) s;
          } else {
            if (r != 15)
              goto EndOfBlock;
            k += 15;
          }
        }
      } else {
        if (s) {
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          DROP_BITS(s);
        }
      }

      /* Section F.2.2.2: decode the AC coefficients */
      /* In this path we just discard the values */
      for (; k <= Se; k++) {
        HUFF_DECODE(s, br_state, htbl, return FALSE, label3);

        r = s >> 4;
        s &= 15;

        if (s) {
          k += r;
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          DROP_BITS(s);
        } else {
          if (r != 15)
            break;
          k += 15;
        }
      }

      EndOfBlock: ;
    }

    /* Completed MCU, so update state */
    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(entropy->saved, state);
  }

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * Decode one MCU's worth of Huffman-compressed coefficients,
 * full-size blocks.
 */

METHODDEF(boolean)
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int blkn;
  BITREAD_STATE_VARS;
  savable_state state;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
        return FALSE;
  }

  /* If we've run out of data, just leave the MCU set to zeroes.
   * This way, we return uniform gray for the remainder of the segment.
   */
  if (! entropy->insufficient_data) {

    /* Load up working state */
    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(state, entropy->saved);

    /* Outer loop handles each block in the MCU */

    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      JBLOCKROW block = MCU_data[blkn];
      d_derived_tbl * htbl;
      register int s, k, r;
      int coef_limit, ci;

      /* Decode a single block's worth of coefficients */

      /* Section F.2.2.1: decode the DC coefficient difference */
      htbl = entropy->dc_cur_tbls[blkn];
      HUFF_DECODE(s, br_state, htbl, return FALSE, label1);

      htbl = entropy->ac_cur_tbls[blkn];
      k = 1;
      coef_limit = entropy->coef_limit[blkn];
      if (coef_limit) {
        /* Convert DC difference to actual value, update last_dc_val */
        if (s) {
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          r = GET_BITS(s);
          s = HUFF_EXTEND(r, s);
        }
        ci = cinfo->MCU_membership[blkn];
        s += state.last_dc_val[ci];
        state.last_dc_val[ci] = s;
        /* Output the DC coefficient */
        (*block)[0] = (JCOEF) s;

        /* Section F.2.2.2: decode the AC coefficients */
        /* Since zeroes are skipped, output area must be cleared beforehand */
        for (; k < coef_limit; k++) {
          HUFF_DECODE(s, br_state, htbl, return FALSE, label2);

          r = s >> 4;
          s &= 15;

          if (s) {
            k += r;
            CHECK_BIT_BUFFER(br_state, s, return FALSE);
            r = GET_BITS(s);
            s = HUFF_EXTEND(r, s);
            /* Output coefficient in natural (dezigzagged) order.
             * Note: the extra entries in jpeg_natural_order[] will save us
             * if k >= DCTSIZE2, which could happen if the data is corrupted.
             */
            (*block)[jpeg_natural_order[k]] = (JCOEF) s;
          } else {
            if (r != 15)
              goto EndOfBlock;
            k += 15;
          }
        }
      } else {
        if (s) {
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          DROP_BITS(s);
        }
      }

      /* Section F.2.2.2: decode the AC coefficients */
      /* In this path we just discard the values */
      for (; k < DCTSIZE2; k++) {
        HUFF_DECODE(s, br_state, htbl, return FALSE, label3);

        r = s >> 4;
        s &= 15;

        if (s) {
          k += r;
          CHECK_BIT_BUFFER(br_state, s, return FALSE);
          DROP_BITS(s);
        } else {
          if (r != 15)
            break;
          k += 15;
        }
      }

      EndOfBlock: ;
    }

    /* Completed MCU, so update state */
    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
    ASSIGN_STATE(entropy->saved, state);
  }

  /* Account for restart interval (no-op if not using restarts) */
  entropy->restarts_to_go--;

  return TRUE;
}


/*
 * Initialize for a Huffman-compressed scan.
 */

METHODDEF(void)
start_pass_huff_decoder (j_decompress_ptr cinfo)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int ci, blkn, tbl, i;
  jpeg_component_info * compptr;

  if (cinfo->progressive_mode) {
    /* Validate progressive scan parameters */
    if (cinfo->Ss == 0) {
      if (cinfo->Se != 0)
        goto bad;
    } else {
      /* need not check Ss/Se < 0 since they came from unsigned bytes */
      if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)
        goto bad;
      /* AC scans may have only one component */
      if (cinfo->comps_in_scan != 1)
        goto bad;
    }
    if (cinfo->Ah != 0) {
      /* Successive approximation refinement scan: must have Al = Ah-1. */
      if (cinfo->Ah-1 != cinfo->Al)
        goto bad;
    }
    if (cinfo->Al > 13) {       /* need not check for < 0 */
      /* Arguably the maximum Al value should be less than 13 for 8-bit precision,
       * but the spec doesn't say so, and we try to be liberal about what we
       * accept.  Note: large Al values could result in out-of-range DC
       * coefficients during early scans, leading to bizarre displays due to
       * overflows in the IDCT math.  But we won't crash.
       */
      bad:
      ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
               cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
    }
    /* Update progression status, and verify that scan order is legal.
     * Note that inter-scan inconsistencies are treated as warnings
     * not fatal errors ... not clear if this is right way to behave.
     */
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
      int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
      if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
        WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
      for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
        int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
        if (cinfo->Ah != expected)
          WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
        coef_bit_ptr[coefi] = cinfo->Al;
      }
    }

    /* Select MCU decoding routine */
    if (cinfo->Ah == 0) {
      if (cinfo->Ss == 0)
        entropy->pub.decode_mcu = decode_mcu_DC_first;
      else
        entropy->pub.decode_mcu = decode_mcu_AC_first;
    } else {
      if (cinfo->Ss == 0)
        entropy->pub.decode_mcu = decode_mcu_DC_refine;
      else
        entropy->pub.decode_mcu = decode_mcu_AC_refine;
    }

    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      /* Make sure requested tables are present, and compute derived tables.
       * We may build same derived table more than once, but it's not expensive.
       */
      if (cinfo->Ss == 0) {
        if (cinfo->Ah == 0) {   /* DC refinement needs no table */
          tbl = compptr->dc_tbl_no;
          jpeg_make_d_derived_tbl(cinfo, TRUE, tbl,
                                  & entropy->derived_tbls[tbl]);
        }
      } else {
        tbl = compptr->ac_tbl_no;
        jpeg_make_d_derived_tbl(cinfo, FALSE, tbl,
                                & entropy->derived_tbls[tbl]);
        /* remember the single active table */
        entropy->ac_derived_tbl = entropy->derived_tbls[tbl];
      }
      /* Initialize DC predictions to 0 */
      entropy->saved.last_dc_val[ci] = 0;
    }

    /* Initialize private state variables */
    entropy->saved.EOBRUN = 0;
  } else {
    /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
     * This ought to be an error condition, but we make it a warning because
     * there are some baseline files out there with all zeroes in these bytes.
     */
    if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
        ((cinfo->is_baseline || cinfo->Se < DCTSIZE2) &&
        cinfo->Se != cinfo->lim_Se))
      WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);

    /* Select MCU decoding routine */
    /* We retain the hard-coded case for full-size blocks.
     * This is not necessary, but it appears that this version is slightly
     * more performant in the given implementation.
     * With an improved implementation we would prefer a single optimized
     * function.
     */
    if (cinfo->lim_Se != DCTSIZE2-1)
      entropy->pub.decode_mcu = decode_mcu_sub;
    else
      entropy->pub.decode_mcu = decode_mcu;

    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      compptr = cinfo->cur_comp_info[ci];
      /* Compute derived values for Huffman tables */
      /* We may do this more than once for a table, but it's not expensive */
      tbl = compptr->dc_tbl_no;
      jpeg_make_d_derived_tbl(cinfo, TRUE, tbl,
                              & entropy->dc_derived_tbls[tbl]);
      if (cinfo->lim_Se) {      /* AC needs no table when not present */
        tbl = compptr->ac_tbl_no;
        jpeg_make_d_derived_tbl(cinfo, FALSE, tbl,
                                & entropy->ac_derived_tbls[tbl]);
      }
      /* Initialize DC predictions to 0 */
      entropy->saved.last_dc_val[ci] = 0;
    }

    /* Precalculate decoding info for each block in an MCU of this scan */
    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
      ci = cinfo->MCU_membership[blkn];
      compptr = cinfo->cur_comp_info[ci];
      /* Precalculate which table to use for each block */
      entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
      entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
      /* Decide whether we really care about the coefficient values */
      if (compptr->component_needed) {
        ci = compptr->DCT_v_scaled_size;
        i = compptr->DCT_h_scaled_size;
        switch (cinfo->lim_Se) {
        case (1*1-1):
          entropy->coef_limit[blkn] = 1;
          break;
        case (2*2-1):
          if (ci <= 0 || ci > 2) ci = 2;
          if (i <= 0 || i > 2) i = 2;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order2[ci - 1][i - 1];
          break;
        case (3*3-1):
          if (ci <= 0 || ci > 3) ci = 3;
          if (i <= 0 || i > 3) i = 3;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order3[ci - 1][i - 1];
          break;
        case (4*4-1):
          if (ci <= 0 || ci > 4) ci = 4;
          if (i <= 0 || i > 4) i = 4;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order4[ci - 1][i - 1];
          break;
        case (5*5-1):
          if (ci <= 0 || ci > 5) ci = 5;
          if (i <= 0 || i > 5) i = 5;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order5[ci - 1][i - 1];
          break;
        case (6*6-1):
          if (ci <= 0 || ci > 6) ci = 6;
          if (i <= 0 || i > 6) i = 6;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order6[ci - 1][i - 1];
          break;
        case (7*7-1):
          if (ci <= 0 || ci > 7) ci = 7;
          if (i <= 0 || i > 7) i = 7;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order7[ci - 1][i - 1];
          break;
        default:
          if (ci <= 0 || ci > 8) ci = 8;
          if (i <= 0 || i > 8) i = 8;
          entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order[ci - 1][i - 1];
          break;
        }
      } else {
        entropy->coef_limit[blkn] = 0;
      }
    }
  }

  /* Initialize bitread state variables */
  entropy->bitstate.bits_left = 0;
  entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
  entropy->insufficient_data = FALSE;

  /* Initialize restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;
}


/*
 * Module initialization routine for Huffman entropy decoding.
 */

GLOBAL(void)
jinit_huff_decoder (j_decompress_ptr cinfo)
{
  huff_entropy_ptr entropy;
  int i;

  entropy = (huff_entropy_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                SIZEOF(huff_entropy_decoder));
  cinfo->entropy = &entropy->pub;
  entropy->pub.start_pass = start_pass_huff_decoder;

  if (cinfo->progressive_mode) {
    /* Create progression status table */
    int *coef_bit_ptr, ci;
    cinfo->coef_bits = (int (*)[DCTSIZE2])
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
                                  cinfo->num_components*DCTSIZE2*SIZEOF(int));
    coef_bit_ptr = & cinfo->coef_bits[0][0];
    for (ci = 0; ci < cinfo->num_components; ci++)
      for (i = 0; i < DCTSIZE2; i++)
        *coef_bit_ptr++ = -1;

    /* Mark derived tables unallocated */
    for (i = 0; i < NUM_HUFF_TBLS; i++) {
      entropy->derived_tbls[i] = NULL;
    }
  } else {
    /* Mark tables unallocated */
    for (i = 0; i < NUM_HUFF_TBLS; i++) {
      entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
    }
  }
}

/* [<][>][^][v][top][bottom][index][help] */