text: /*
   * jdhuff.c
   *
   * Copyright (C) 1991-1998, 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 which are shared
   * by the sequential, progressive and lossless decoders.
   */
  
  #define JPEG_INTERNALS
  #include "jinclude.h"
  #include "jpeglib.h"
  #include "jlossy.h"    /* Private declarations for lossy codec */
  #include "jlossls.h"    /* Private declarations for lossless codec */
  #include "jdhuff.h"    /* Declarations shared with jd*huff.c */
  
  
  /*
   * Compute the derived values for a Huffman table.
   * This routine also performs some validation checks on the table.
   */
  
  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.
       * BUG FIX 2001-09-03: Comparison must be >, not >=
       */
      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..16.
     * (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];
  /* The following file contains a value of 17 in the huffman table, which is impossible
   * according to ISO 10918-1, H.1.2.2 Huffman coding of the modulo difference
   * and table H.2.
   * PHILIPS_Gyroscan-12-Jpeg_Extended_Process_2_4.dcm
   * MM, 2008/08/12 I am breaking backward compatibility and decide not to support this image
   * anymore. In fact the decompression using another library: PVRG was giving me
   * another result anyway.
   *
   * Steps:
   *
   * $ gdcmconv --raw -i PHILIPS_Gyroscan-12-Jpeg_Extended_Process_2_4.dcm -o bla.dcm
   * $ gdcmraw -i bla.dcm -o bla.raw
   * $ gdcmraw -i PHILIPS_Gyroscan-12-Jpeg_Extended_Process_2_4.dcm -o philips.jpg
   * $ pvrgjpeg -d philips
   * $ dd conv=swab if=philips.jpg.0 of=philips.raw
   * $ vbindiff bla.raw philips.raw
   *
   * $ md5sum bla.raw philips.raw
   * 4b0021efe5a675f24c82e1ff28a1e2eb  bla.raw
   * d93d2f78d845c7a132489aab92eadd32  philips.raw
   *
   *
   * footnote, I get a much closer result doing:
   * $ pvrgjpeg -a -y -d philips
   * after that the number of diff with IJG is getting lower
   *
   * 0f2570f5d91ddea5bd9d3825a86eaabe  philips.raw
   */
        if (sym < 0 || sym > 16)
    ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
      }
    }
  }
  
  
  /*
   * Out-of-line code for bit fetching.
   * 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.
         */
        huffd_common_ptr huffd;
        if (cinfo->process == JPROC_LOSSLESS)
    huffd = (huffd_common_ptr) ((j_lossless_d_ptr) cinfo->codec)->entropy_private;
        else
    huffd = (huffd_common_ptr) ((j_lossy_d_ptr) cinfo->codec)->entropy_private;
        if (! huffd->insufficient_data) {
    WARNMS(cinfo, JWRN_HIT_MARKER);
    huffd->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]) ];
  }
  