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/*

 * 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 */

  boolean dc_needed[D_MAX_BLOCKS_IN_MCU];

  boolean 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, 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 (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(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 (! 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 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]) ];

}

/*

 * 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(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;

  /* 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(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->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;

  }

}