/*

 * 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 "jinclude8.h"

#include "jpeglib8.h"

#include "jlossy8.h"        /* Private declarations for lossy codec */

#include "jlossls8.h"       /* Private declarations for lossless codec */

#include "jdhuff8.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: Comparison must be >, not >=

     */

    if (((IJG_INT32) code) > (((IJG_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] = (IJG_INT32) p - (IJG_INT32) huffcode[p];

      p += htbl->bits[l];

      dtbl->maxcode[l] = (IJG_INT32)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 = (int)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];

      if (sym < 0 || sym > 16)

#ifdef DCMTK_ENABLE_STRICT_HUFFMAN_TABLE_CHECK

    ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);

#else

    TRACEMS1(cinfo, 1, JTRC_UNOPT_HUFF_TABLE, sym);

#endif

    }

  }

}

/*

 * 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 IJG_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]) ];

}