src/tiff/contrib/ojpeg/jdhuff_add.c

   1 /*
   2  * BEWARE OF KLUDGE:  This subroutine is a hack for decoding illegal JPEG-in-
   3  *                    TIFF encapsulations produced by Microsoft's Wang Imaging
   4  * for Windows application with the public-domain TIFF Library.  Based upon an
   5  * examination of selected output files, this program apparently divides a JPEG
   6  * bit-stream into consecutive horizontal TIFF "strips", such that the JPEG
   7  * encoder's/decoder's DC coefficients for each image component are reset before
   8  * each "strip".  Moreover, a "strip" is not necessarily encoded in a multiple
   9  * of 8 bits, so one must sometimes discard 1-7 bits at the end of each "strip"
  10  * for alignment to the next input-Byte storage boundary.  IJG JPEG Library
  11  * decoder state is not normally exposed to client applications, so this sub-
  12  * routine provides the TIFF Library with a "hook" to make these corrections.
  13  * It should be called after "jpeg_start_decompress()" and before
  14  * "jpeg_finish_decompress()", just before decoding each "strip" using
  15  * "jpeg_read_raw_data()" or "jpeg_read_scanlines()".
  16  *
  17  * This kludge is not sanctioned or supported by the Independent JPEG Group, and
  18  * future changes to the IJG JPEG Library might invalidate it.  Do not send bug
  19  * reports about this code to IJG developers.  Instead, contact the author for
  20  * advice: Scott B. Marovich <marovich@hpl.hp.com>, Hewlett-Packard Labs, 6/01.
  21  */
  22 GLOBAL(void)
  23 jpeg_reset_huff_decode (register j_decompress_ptr cinfo,register float *refbw)
  24 { register huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
  25   register int ci = 0;
  26
  27   /* Re-initialize DC predictions */
  28   do entropy->saved.last_dc_val[ci] = -refbw[ci << 1];
  29   while (++ci < cinfo->comps_in_scan);
  30   /* Discard encoded input bits, up to the next Byte boundary */
  31   entropy->bitstate.bits_left &= ~7;
  32 }