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 /*

  * reserved comment block

  * DO NOT REMOVE OR ALTER!

  */

 /*

  * 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;

   }

 }