text: /*
   * jdhuff.c
   *
   * Copyright (C) 1991-1995, 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];
  } 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, 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;
      /* Make sure requested tables are present */
      if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS ||
  	cinfo->dc_huff_tbl_ptrs[dctbl] == NULL)
        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
      if (actbl < 0 || actbl >= NUM_HUFF_TBLS ||
  	cinfo->ac_huff_tbl_ptrs[actbl] == NULL)
        ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
      /* 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, cinfo->dc_huff_tbl_ptrs[dctbl],
  			    & entropy->dc_derived_tbls[dctbl]);
      jpeg_make_d_derived_tbl(cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
  			    & entropy->ac_derived_tbls[actbl]);
      /* Initialize DC predictions to 0 */
      entropy->saved.last_dc_val[ci] = 0;
    }
  
    /* Initialize bitread state variables */
    entropy->bitstate.bits_left = 0;
    entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
    entropy->bitstate.printed_eod = FALSE;
  
    /* Initialize restart counter */
    entropy->restarts_to_go = cinfo->restart_interval;
  }
  
  
  /*
   * Compute the derived values for a Huffman table.
   * Note this is also used by jdphuff.c.
   */
  
  GLOBAL void
  jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, JHUFF_TBL * htbl,
  			 d_derived_tbl ** pdtbl)
  {
    d_derived_tbl *dtbl;
    int p, i, l, si;
    int lookbits, ctr;
    char huffsize[257];
    unsigned int huffcode[257];
    unsigned int code;
  
    /* 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 */
    /* Note that this is in code-length order. */
  
    p = 0;
    for (l = 1; l <= 16; l++) {
      for (i = 1; i <= (int) htbl->bits[l]; i++)
        huffsize[p++] = (char) l;
    }
    huffsize[p] = 0;
    
    /* Figure C.2: generate the codes themselves */
    /* Note that this is in code-length order. */
    
    code = 0;
    si = huffsize[0];
    p = 0;
    while (huffsize[p]) {
      while (((int) huffsize[p]) == si) {
        huffcode[p++] = code;
        code++;
      }
      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]) {
        dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */
        dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */
        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++;
        }
      }
    }
  }
  
  
  /*
   * 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;
    register int c;
  
    /* 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.) */
  
    while (bits_left < MIN_GET_BITS) {
      /* Attempt to read a byte */
      if (state->unread_marker != 0)
        goto no_more_data;	/* can't advance past a marker */
  
      if (bytes_in_buffer == 0) {
        if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
  	return FALSE;
        next_input_byte = state->cinfo->src->next_input_byte;
        bytes_in_buffer = state->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) {
        do {
  	if (bytes_in_buffer == 0) {
  	  if (! (*state->cinfo->src->fill_input_buffer) (state->cinfo))
  	    return FALSE;
  	  next_input_byte = state->cinfo->src->next_input_byte;
  	  bytes_in_buffer = state->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. */
  	/* Better put it back for use later */
  	state->unread_marker = c;
  
        no_more_data:
  	/* There should be enough bits still left in the data segment; */
  	/* if so, just break out of the outer while loop. */
  	if (bits_left >= nbits)
  	  break;
  	/* Uh-oh.  Report corrupted data to user and stuff zeroes into
  	 * the data stream, so that we can produce some kind of image.
  	 * Note that this code will be repeated for each byte demanded
  	 * for the rest of the segment.  We use a nonvolatile flag to ensure
  	 * that only one warning message appears.
  	 */
  	if (! *(state->printed_eod_ptr)) {
  	  WARNMS(state->cinfo, JWRN_HIT_MARKER);
  	  *(state->printed_eod_ptr) = TRUE;
  	}
  	c = 0;			/* insert a zero byte into bit buffer */
        }
      }
  
      /* OK, load c into get_buffer */
      get_buffer = (get_buffer << 8) | c;
      bits_left += 8;
    }
  
    /* 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[ htbl->valptr[l] +
  			    ((int) (code - htbl->mincode[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;
  
    /* Next segment can get another out-of-data warning */
    entropy->bitstate.printed_eod = 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;
    register int s, k, r;
    int blkn, ci;
    JBLOCKROW block;
    BITREAD_STATE_VARS;
    savable_state state;
    d_derived_tbl * dctbl;
    d_derived_tbl * actbl;
    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;
    }
  
    /* 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];
      dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];
      actbl = entropy->ac_derived_tbls[compptr->ac_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, dctbl, return FALSE, label1);
      if (s) {
        CHECK_BIT_BUFFER(br_state, s, return FALSE);
        r = GET_BITS(s);
        s = HUFF_EXTEND(r, s);
      }
  
      /* Shortcut if component's values are not interesting */
      if (! compptr->component_needed)
        goto skip_ACs;
  
      /* Convert DC difference to actual value, update last_dc_val */
      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;
  
      /* Do we need to decode the AC coefficients for this component? */
      if (compptr->DCT_scaled_size > 1) {
  
        /* 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 {
  skip_ACs:
  
        /* 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;
    }
  }
  