    /*
     * jdhuff.c
     *
     * Copyright (C) 1991-1997, Thomas G. Lane.
     * 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.
     *
     * 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"
    #include "jdhuff.h"		/* Declarations shared with jdphuff.c */

    /*
     * 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 {
      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).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. */
      unsigned int restarts_to_go;	/* MCUs left in this restart interval */

      /* 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 dc_needed[D_MAX_BLOCKS_IN_MCU];
      int ac_needed[D_MAX_BLOCKS_IN_MCU];
    } huff_entropy_decoder;

    typedef huff_entropy_decoder * huff_entropy_ptr;

    /*
     * 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, dctbl, actbl;
      jpeg_component_info * compptr;

      /* 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->Se != DCTSIZE2-1 ||
          cinfo->Ah != 0 || cinfo->Al != 0)
        WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);

      for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
        compptr = cinfo->cur_comp_info[ci];
        dctbl = compptr->dc_tbl_no;
        actbl = compptr->ac_tbl_no;
        /* Compute derived values for Huffman tables */
        /* We may do this more than once for a table, but it's not expensive */
        jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
    			    & entropy->dc_derived_tbls[dctbl]);
        jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
    			    & entropy->ac_derived_tbls[actbl]);
        /* 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) {
          entropy->dc_needed[blkn] = TRUE;
          /* we don't need the ACs if producing a 1/8th-size image */
          entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
        } else {
          entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
        }
      }

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

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

    /*
     * Compute the derived values for a Huffman table.
     * This routine also performs some validation checks on the table.
     *
     * Note this is also used by jdphuff.c.
     */

    GLOBAL(void)
    jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, int 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 (((long) code) >= (((long) 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] = (long) p - (long) 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 (shared with jdphuff.c).
     * See jdhuff.h for info about usage.
     * 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

    GLOBAL(int)
    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 (! cinfo->entropy->insufficient_data) {
    	WARNMS(cinfo, JWRN_HIT_MARKER);
    	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;
    }

    /*
     * Out-of-line code for Huffman code decoding.
     * See jdhuff.h for info about usage.
     */

    GLOBAL(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 long 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]) ];
    }

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

    #ifdef AVOID_TABLES

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

    #else

    #define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))

    static const int extend_test[16] =   /* entry n is 2**(n-1) */
      { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
        0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };

    static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
      { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
        ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
        ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
        ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };

    #endif /* AVOID_TABLES */

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

    LOCAL(int)
    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;

      /* 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->pub.insufficient_data = FALSE;

      return TRUE;
    }

    /*
     * Decode and return 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 HAS BEEN ZEROED BY THE CALLER.
     * (Wholesale zeroing is usually a little faster than retail...)
     *
     * Returns 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
     * this module, since we'll just re-assign them on the next call.)
     */

    METHODDEF(int)
    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->pub.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 * dctbl = entropy->dc_cur_tbls[blkn];
          d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
          register int s, k, r;

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

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

          if (entropy->dc_needed[blkn]) {
    	/* Convert DC difference to actual value, update last_dc_val */
    	int ci = cinfo->MCU_membership[blkn];
    	s += state.last_dc_val[ci];
    	state.last_dc_val[ci] = s;
    	/* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
    	(*block)[0] = (JCOEF) s;
          }

          if (entropy->ac_needed[blkn]) {

    	/* Section F.2.2.2: decode the AC coefficients */
    	/* Since zeroes are skipped, output area must be cleared beforehand */
    	for (k = 1; k < DCTSIZE2; k++) {
    	  HUFF_DECODE(s, br_state, actbl, 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)
    	      break;
    	    k += 15;
    	  }
    	}

          } else {

    	/* Section F.2.2.2: decode the AC coefficients */
    	/* In this path we just discard the values */
    	for (k = 1; k < DCTSIZE2; k++) {
    	  HUFF_DECODE(s, br_state, actbl, 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;
    	  }
    	}

          }
        }

        /* 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;
    }

    /*
     * 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 = (struct jpeg_entropy_decoder *) entropy;
      entropy->pub.start_pass = start_pass_huff_decoder;
      entropy->pub.decode_mcu = decode_mcu;

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