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tif_lzw.c

/* $Id: tif_lzw.c,v 1.28 2006/03/16 12:38:24 dron Exp $ */

/*
 * Copyright (c) 1988-1997 Sam Leffler
 * Copyright (c) 1991-1997 Silicon Graphics, Inc.
 *
 * Permission to use, copy, modify, distribute, and sell this software and 
 * its documentation for any purpose is hereby granted without fee, provided
 * that (i) the above copyright notices and this permission notice appear in
 * all copies of the software and related documentation, and (ii) the names of
 * Sam Leffler and Silicon Graphics may not be used in any advertising or
 * publicity relating to the software without the specific, prior written
 * permission of Sam Leffler and Silicon Graphics.
 * 
 * THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND, 
 * EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY 
 * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  
 * 
 * IN NO EVENT SHALL SAM LEFFLER OR SILICON GRAPHICS BE LIABLE FOR
 * ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND,
 * OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
 * WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF 
 * LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE 
 * OF THIS SOFTWARE.
 */

#include "tiffiop.h"
#ifdef LZW_SUPPORT
/*
 * TIFF Library.
 * Rev 5.0 Lempel-Ziv & Welch Compression Support
 *
 * This code is derived from the compress program whose code is
 * derived from software contributed to Berkeley by James A. Woods,
 * derived from original work by Spencer Thomas and Joseph Orost.
 *
 * The original Berkeley copyright notice appears below in its entirety.
 */
#include "tif_predict.h"

#include <stdio.h>

/*
 * NB: The 5.0 spec describes a different algorithm than Aldus
 *     implements.  Specifically, Aldus does code length transitions
 *     one code earlier than should be done (for real LZW).
 *     Earlier versions of this library implemented the correct
 *     LZW algorithm, but emitted codes in a bit order opposite
 *     to the TIFF spec.  Thus, to maintain compatibility w/ Aldus
 *     we interpret MSB-LSB ordered codes to be images written w/
 *     old versions of this library, but otherwise adhere to the
 *     Aldus "off by one" algorithm.
 *
 * Future revisions to the TIFF spec are expected to "clarify this issue".
 */
#define     LZW_COMPAT        /* include backwards compatibility code */
/*
 * Each strip of data is supposed to be terminated by a CODE_EOI.
 * If the following #define is included, the decoder will also
 * check for end-of-strip w/o seeing this code.  This makes the
 * library more robust, but also slower.
 */
#define     LZW_CHECKEOS            /* include checks for strips w/o EOI code */

#define MAXCODE(n)      ((1L<<(n))-1)
/*
 * The TIFF spec specifies that encoded bit
 * strings range from 9 to 12 bits.
 */
#define     BITS_MIN    9           /* start with 9 bits */
#define     BITS_MAX    12          /* max of 12 bit strings */
/* predefined codes */
#define     CODE_CLEAR  256         /* code to clear string table */
#define     CODE_EOI    257         /* end-of-information code */
#define CODE_FIRST      258         /* first free code entry */
#define     CODE_MAX    MAXCODE(BITS_MAX)
#define     HSIZE       9001L       /* 91% occupancy */
#define     HSHIFT            (13-8)
#ifdef LZW_COMPAT
/* NB: +1024 is for compatibility with old files */
#define     CSIZE       (MAXCODE(BITS_MAX)+1024L)
#else
#define     CSIZE       (MAXCODE(BITS_MAX)+1L)
#endif

/*
 * State block for each open TIFF file using LZW
 * compression/decompression.  Note that the predictor
 * state block must be first in this data structure.
 */
typedef     struct {
      TIFFPredictorState predict;   /* predictor super class */

      unsigned short    nbits;            /* # of bits/code */
      unsigned short    maxcode;    /* maximum code for lzw_nbits */
      unsigned short    free_ent;   /* next free entry in hash table */
      long        nextdata;   /* next bits of i/o */
      long        nextbits;   /* # of valid bits in lzw_nextdata */

        int             rw_mode;        /* preserve rw_mode from init */
} LZWBaseState;

#define     lzw_nbits   base.nbits
#define     lzw_maxcode base.maxcode
#define     lzw_free_ent      base.free_ent
#define     lzw_nextdata      base.nextdata
#define     lzw_nextbits      base.nextbits

/*
 * Encoding-specific state.
 */
typedef uint16 hcode_t;             /* codes fit in 16 bits */
typedef struct {
      long  hash;
      hcode_t     code;
} hash_t;

/*
 * Decoding-specific state.
 */
typedef struct code_ent {
      struct code_ent *next;
      unsigned short    length;           /* string len, including this token */
      unsigned char     value;            /* data value */
      unsigned char     firstchar;  /* first token of string */
} code_t;

typedef     int (*decodeFunc)(TIFF*, tidata_t, tsize_t, tsample_t);

typedef struct {
      LZWBaseState base;

      /* Decoding specific data */
      long  dec_nbitsmask;          /* lzw_nbits 1 bits, right adjusted */
      long  dec_restart;            /* restart count */
#ifdef LZW_CHECKEOS
      long  dec_bitsleft;           /* available bits in raw data */
#endif
      decodeFunc dec_decode;        /* regular or backwards compatible */
      code_t*     dec_codep;        /* current recognized code */
      code_t*     dec_oldcodep;           /* previously recognized code */
      code_t*     dec_free_entp;          /* next free entry */
      code_t*     dec_maxcodep;           /* max available entry */
      code_t*     dec_codetab;            /* kept separate for small machines */

      /* Encoding specific data */
      int   enc_oldcode;            /* last code encountered */
      long  enc_checkpoint;         /* point at which to clear table */
#define CHECK_GAP 10000       /* enc_ratio check interval */
      long  enc_ratio;        /* current compression ratio */
      long  enc_incount;            /* (input) data bytes encoded */
      long  enc_outcount;           /* encoded (output) bytes */
      tidata_t enc_rawlimit;        /* bound on tif_rawdata buffer */
      hash_t*     enc_hashtab;            /* kept separate for small machines */
} LZWCodecState;

#define     LZWState(tif)           ((LZWBaseState*) (tif)->tif_data)
#define     DecoderState(tif) ((LZWCodecState*) LZWState(tif))
#define     EncoderState(tif) ((LZWCodecState*) LZWState(tif))

static      int LZWDecode(TIFF*, tidata_t, tsize_t, tsample_t);
#ifdef LZW_COMPAT
static      int LZWDecodeCompat(TIFF*, tidata_t, tsize_t, tsample_t);
#endif
static  void cl_hash(LZWCodecState*);

/*
 * LZW Decoder.
 */

#ifdef LZW_CHECKEOS
/*
 * This check shouldn't be necessary because each
 * strip is suppose to be terminated with CODE_EOI.
 */
#define     NextCode(_tif, _sp, _bp, _code, _get) {                     \
      if ((_sp)->dec_bitsleft < nbits) {                    \
            TIFFWarningExt(_tif->tif_clientdata, _tif->tif_name,                    \
                "LZWDecode: Strip %d not terminated with EOI code", \
                _tif->tif_curstrip);                        \
            _code = CODE_EOI;                         \
      } else {                                        \
            _get(_sp,_bp,_code);                            \
            (_sp)->dec_bitsleft -= nbits;                   \
      }                                               \
}
#else
#define     NextCode(tif, sp, bp, code, get) get(sp, bp, code)
#endif

static int
LZWSetupDecode(TIFF* tif)
{
      LZWCodecState* sp = DecoderState(tif);
      static const char module[] = " LZWSetupDecode";
      int code;

        if( sp == NULL )
        {
            /*
             * Allocate state block so tag methods have storage to record 
                   * values.
             */
            tif->tif_data = (tidata_t) _TIFFmalloc(sizeof(LZWCodecState));
            if (tif->tif_data == NULL)
            {
                        TIFFErrorExt(tif->tif_clientdata, "LZWPreDecode", "No space for LZW state block");
                return (0);
            }

            DecoderState(tif)->dec_codetab = NULL;
            DecoderState(tif)->dec_decode = NULL;
            
            /*
             * Setup predictor setup.
             */
            (void) TIFFPredictorInit(tif);

            sp = DecoderState(tif);
        }
            
      assert(sp != NULL);

      if (sp->dec_codetab == NULL) {
            sp->dec_codetab = (code_t*)_TIFFmalloc(CSIZE*sizeof (code_t));
            if (sp->dec_codetab == NULL) {
                  TIFFErrorExt(tif->tif_clientdata, module, "No space for LZW code table");
                  return (0);
            }
            /*
             * Pre-load the table.
             */
                code = 255;
                do {
                    sp->dec_codetab[code].value = code;
                    sp->dec_codetab[code].firstchar = code;
                    sp->dec_codetab[code].length = 1;
                    sp->dec_codetab[code].next = NULL;
                } while (code--);
      }
      return (1);
}

/*
 * Setup state for decoding a strip.
 */
static int
LZWPreDecode(TIFF* tif, tsample_t s)
{
      LZWCodecState *sp = DecoderState(tif);

      (void) s;
      assert(sp != NULL);
      /*
       * Check for old bit-reversed codes.
       */
      if (tif->tif_rawdata[0] == 0 && (tif->tif_rawdata[1] & 0x1)) {
#ifdef LZW_COMPAT
            if (!sp->dec_decode) {
                  TIFFWarningExt(tif->tif_clientdata, tif->tif_name,
                      "Old-style LZW codes, convert file");
                  /*
                   * Override default decoding methods with
                   * ones that deal with the old coding.
                   * Otherwise the predictor versions set
                   * above will call the compatibility routines
                   * through the dec_decode method.
                   */
                  tif->tif_decoderow = LZWDecodeCompat;
                  tif->tif_decodestrip = LZWDecodeCompat;
                  tif->tif_decodetile = LZWDecodeCompat;
                  /*
                   * If doing horizontal differencing, must
                   * re-setup the predictor logic since we
                   * switched the basic decoder methods...
                   */
                  (*tif->tif_setupdecode)(tif);
                  sp->dec_decode = LZWDecodeCompat;
            }
            sp->lzw_maxcode = MAXCODE(BITS_MIN);
#else /* !LZW_COMPAT */
            if (!sp->dec_decode) {
                  TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                      "Old-style LZW codes not supported");
                  sp->dec_decode = LZWDecode;
            }
            return (0);
#endif/* !LZW_COMPAT */
      } else {
            sp->lzw_maxcode = MAXCODE(BITS_MIN)-1;
            sp->dec_decode = LZWDecode;
      }
      sp->lzw_nbits = BITS_MIN;
      sp->lzw_nextbits = 0;
      sp->lzw_nextdata = 0;

      sp->dec_restart = 0;
      sp->dec_nbitsmask = MAXCODE(BITS_MIN);
#ifdef LZW_CHECKEOS
      sp->dec_bitsleft = tif->tif_rawcc << 3;
#endif
      sp->dec_free_entp = sp->dec_codetab + CODE_FIRST;
      /*
       * Zero entries that are not yet filled in.  We do
       * this to guard against bogus input data that causes
       * us to index into undefined entries.  If you can
       * come up with a way to safely bounds-check input codes
       * while decoding then you can remove this operation.
       */
      _TIFFmemset(sp->dec_free_entp, 0, (CSIZE-CODE_FIRST)*sizeof (code_t));
      sp->dec_oldcodep = &sp->dec_codetab[-1];
      sp->dec_maxcodep = &sp->dec_codetab[sp->dec_nbitsmask-1];
      return (1);
}

/*
 * Decode a "hunk of data".
 */
#define     GetNextCode(sp, bp, code) {                     \
      nextdata = (nextdata<<8) | *(bp)++;             \
      nextbits += 8;                                  \
      if (nextbits < nbits) {                         \
            nextdata = (nextdata<<8) | *(bp)++;       \
            nextbits += 8;                            \
      }                                         \
      code = (hcode_t)((nextdata >> (nextbits-nbits)) & nbitsmask);     \
      nextbits -= nbits;                              \
}

static void
codeLoop(TIFF* tif)
{
      TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
          "LZWDecode: Bogus encoding, loop in the code table; scanline %d",
          tif->tif_row);
}

static int
LZWDecode(TIFF* tif, tidata_t op0, tsize_t occ0, tsample_t s)
{
      LZWCodecState *sp = DecoderState(tif);
      char *op = (char*) op0;
      long occ = (long) occ0;
      char *tp;
      unsigned char *bp;
      hcode_t code;
      int len;
      long nbits, nextbits, nextdata, nbitsmask;
      code_t *codep, *free_entp, *maxcodep, *oldcodep;

      (void) s;
      assert(sp != NULL);
      /*
       * Restart interrupted output operation.
       */
      if (sp->dec_restart) {
            long residue;

            codep = sp->dec_codep;
            residue = codep->length - sp->dec_restart;
            if (residue > occ) {
                  /*
                   * Residue from previous decode is sufficient
                   * to satisfy decode request.  Skip to the
                   * start of the decoded string, place decoded
                   * values in the output buffer, and return.
                   */
                  sp->dec_restart += occ;
                  do {
                        codep = codep->next;
                  } while (--residue > occ && codep);
                  if (codep) {
                        tp = op + occ;
                        do {
                              *--tp = codep->value;
                              codep = codep->next;
                        } while (--occ && codep);
                  }
                  return (1);
            }
            /*
             * Residue satisfies only part of the decode request.
             */
            op += residue, occ -= residue;
            tp = op;
            do {
                  int t;
                  --tp;
                  t = codep->value;
                  codep = codep->next;
                  *tp = t;
            } while (--residue && codep);
            sp->dec_restart = 0;
      }

      bp = (unsigned char *)tif->tif_rawcp;
      nbits = sp->lzw_nbits;
      nextdata = sp->lzw_nextdata;
      nextbits = sp->lzw_nextbits;
      nbitsmask = sp->dec_nbitsmask;
      oldcodep = sp->dec_oldcodep;
      free_entp = sp->dec_free_entp;
      maxcodep = sp->dec_maxcodep;

      while (occ > 0) {
            NextCode(tif, sp, bp, code, GetNextCode);
            if (code == CODE_EOI)
                  break;
            if (code == CODE_CLEAR) {
                  free_entp = sp->dec_codetab + CODE_FIRST;
                  nbits = BITS_MIN;
                  nbitsmask = MAXCODE(BITS_MIN);
                  maxcodep = sp->dec_codetab + nbitsmask-1;
                  NextCode(tif, sp, bp, code, GetNextCode);
                  if (code == CODE_EOI)
                        break;
                  *op++ = (char)code, occ--;
                  oldcodep = sp->dec_codetab + code;
                  continue;
            }
            codep = sp->dec_codetab + code;

            /*
             * Add the new entry to the code table.
             */
            if (free_entp < &sp->dec_codetab[0] ||
                  free_entp >= &sp->dec_codetab[CSIZE]) {
                  TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                  "LZWDecode: Corrupted LZW table at scanline %d",
                  tif->tif_row);
                  return (0);
            }

            free_entp->next = oldcodep;
            if (free_entp->next < &sp->dec_codetab[0] ||
                  free_entp->next >= &sp->dec_codetab[CSIZE]) {
                  TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                  "LZWDecode: Corrupted LZW table at scanline %d",
                  tif->tif_row);
                  return (0);
            }
            free_entp->firstchar = free_entp->next->firstchar;
            free_entp->length = free_entp->next->length+1;
            free_entp->value = (codep < free_entp) ?
                codep->firstchar : free_entp->firstchar;
            if (++free_entp > maxcodep) {
                  if (++nbits > BITS_MAX)       /* should not happen */
                        nbits = BITS_MAX;
                  nbitsmask = MAXCODE(nbits);
                  maxcodep = sp->dec_codetab + nbitsmask-1;
            }
            oldcodep = codep;
            if (code >= 256) {
                  /*
                   * Code maps to a string, copy string
                   * value to output (written in reverse).
                   */
                  if(codep->length == 0) {
                        TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                      "LZWDecode: Wrong length of decoded string: "
                      "data probably corrupted at scanline %d",
                      tif->tif_row);      
                      return (0);
                  }
                  if (codep->length > occ) {
                        /*
                         * String is too long for decode buffer,
                         * locate portion that will fit, copy to
                         * the decode buffer, and setup restart
                         * logic for the next decoding call.
                         */
                        sp->dec_codep = codep;
                        do {
                              codep = codep->next;
                        } while (codep && codep->length > occ);
                        if (codep) {
                              sp->dec_restart = occ;
                              tp = op + occ;
                              do  {
                                    *--tp = codep->value;
                                    codep = codep->next;
                              }  while (--occ && codep);
                              if (codep)
                                    codeLoop(tif);
                        }
                        break;
                  }
                  len = codep->length;
                  tp = op + len;
                  do {
                        int t;
                        --tp;
                        t = codep->value;
                        codep = codep->next;
                        *tp = t;
                  } while (codep && tp > op);
                  if (codep) {
                      codeLoop(tif);
                      break;
                  }
                  op += len, occ -= len;
            } else
                  *op++ = (char)code, occ--;
      }

      tif->tif_rawcp = (tidata_t) bp;
      sp->lzw_nbits = (unsigned short) nbits;
      sp->lzw_nextdata = nextdata;
      sp->lzw_nextbits = nextbits;
      sp->dec_nbitsmask = nbitsmask;
      sp->dec_oldcodep = oldcodep;
      sp->dec_free_entp = free_entp;
      sp->dec_maxcodep = maxcodep;

      if (occ > 0) {
            TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
            "LZWDecode: Not enough data at scanline %d (short %d bytes)",
                tif->tif_row, occ);
            return (0);
      }
      return (1);
}

#ifdef LZW_COMPAT
/*
 * Decode a "hunk of data" for old images.
 */
#define     GetNextCodeCompat(sp, bp, code) {               \
      nextdata |= (unsigned long) *(bp)++ << nextbits;      \
      nextbits += 8;                                  \
      if (nextbits < nbits) {                         \
            nextdata |= (unsigned long) *(bp)++ << nextbits;\
            nextbits += 8;                            \
      }                                         \
      code = (hcode_t)(nextdata & nbitsmask);               \
      nextdata >>= nbits;                             \
      nextbits -= nbits;                              \
}

static int
LZWDecodeCompat(TIFF* tif, tidata_t op0, tsize_t occ0, tsample_t s)
{
      LZWCodecState *sp = DecoderState(tif);
      char *op = (char*) op0;
      long occ = (long) occ0;
      char *tp;
      unsigned char *bp;
      int code, nbits;
      long nextbits, nextdata, nbitsmask;
      code_t *codep, *free_entp, *maxcodep, *oldcodep;

      (void) s;
      assert(sp != NULL);
      /*
       * Restart interrupted output operation.
       */
      if (sp->dec_restart) {
            long residue;

            codep = sp->dec_codep;
            residue = codep->length - sp->dec_restart;
            if (residue > occ) {
                  /*
                   * Residue from previous decode is sufficient
                   * to satisfy decode request.  Skip to the
                   * start of the decoded string, place decoded
                   * values in the output buffer, and return.
                   */
                  sp->dec_restart += occ;
                  do {
                        codep = codep->next;
                  } while (--residue > occ);
                  tp = op + occ;
                  do {
                        *--tp = codep->value;
                        codep = codep->next;
                  } while (--occ);
                  return (1);
            }
            /*
             * Residue satisfies only part of the decode request.
             */
            op += residue, occ -= residue;
            tp = op;
            do {
                  *--tp = codep->value;
                  codep = codep->next;
            } while (--residue);
            sp->dec_restart = 0;
      }

      bp = (unsigned char *)tif->tif_rawcp;
      nbits = sp->lzw_nbits;
      nextdata = sp->lzw_nextdata;
      nextbits = sp->lzw_nextbits;
      nbitsmask = sp->dec_nbitsmask;
      oldcodep = sp->dec_oldcodep;
      free_entp = sp->dec_free_entp;
      maxcodep = sp->dec_maxcodep;

      while (occ > 0) {
            NextCode(tif, sp, bp, code, GetNextCodeCompat);
            if (code == CODE_EOI)
                  break;
            if (code == CODE_CLEAR) {
                  free_entp = sp->dec_codetab + CODE_FIRST;
                  nbits = BITS_MIN;
                  nbitsmask = MAXCODE(BITS_MIN);
                  maxcodep = sp->dec_codetab + nbitsmask;
                  NextCode(tif, sp, bp, code, GetNextCodeCompat);
                  if (code == CODE_EOI)
                        break;
                  *op++ = code, occ--;
                  oldcodep = sp->dec_codetab + code;
                  continue;
            }
            codep = sp->dec_codetab + code;

            /*
             * Add the new entry to the code table.
             */
            if (free_entp < &sp->dec_codetab[0] ||
                  free_entp >= &sp->dec_codetab[CSIZE]) {
                  TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                  "LZWDecodeCompat: Corrupted LZW table at scanline %d",
                  tif->tif_row);
                  return (0);
            }

            free_entp->next = oldcodep;
            if (free_entp->next < &sp->dec_codetab[0] ||
                  free_entp->next >= &sp->dec_codetab[CSIZE]) {
                  TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                  "LZWDecodeCompat: Corrupted LZW table at scanline %d",
                  tif->tif_row);
                  return (0);
            }
            free_entp->firstchar = free_entp->next->firstchar;
            free_entp->length = free_entp->next->length+1;
            free_entp->value = (codep < free_entp) ?
                codep->firstchar : free_entp->firstchar;
            if (++free_entp > maxcodep) {
                  if (++nbits > BITS_MAX)       /* should not happen */
                        nbits = BITS_MAX;
                  nbitsmask = MAXCODE(nbits);
                  maxcodep = sp->dec_codetab + nbitsmask;
            }
            oldcodep = codep;
            if (code >= 256) {
                  /*
                   * Code maps to a string, copy string
                   * value to output (written in reverse).
                   */
                  if(codep->length == 0) {
                        TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
                      "LZWDecodeCompat: Wrong length of decoded "
                      "string: data probably corrupted at scanline %d",
                      tif->tif_row);      
                      return (0);
                  }
                  if (codep->length > occ) {
                        /*
                         * String is too long for decode buffer,
                         * locate portion that will fit, copy to
                         * the decode buffer, and setup restart
                         * logic for the next decoding call.
                         */
                        sp->dec_codep = codep;
                        do {
                              codep = codep->next;
                        } while (codep->length > occ);
                        sp->dec_restart = occ;
                        tp = op + occ;
                        do  {
                              *--tp = codep->value;
                              codep = codep->next;
                        }  while (--occ);
                        break;
                  }
                  op += codep->length, occ -= codep->length;
                  tp = op;
                  do {
                        *--tp = codep->value;
                  } while( (codep = codep->next) != NULL);
            } else
                  *op++ = code, occ--;
      }

      tif->tif_rawcp = (tidata_t) bp;
      sp->lzw_nbits = nbits;
      sp->lzw_nextdata = nextdata;
      sp->lzw_nextbits = nextbits;
      sp->dec_nbitsmask = nbitsmask;
      sp->dec_oldcodep = oldcodep;
      sp->dec_free_entp = free_entp;
      sp->dec_maxcodep = maxcodep;

      if (occ > 0) {
            TIFFErrorExt(tif->tif_clientdata, tif->tif_name,
          "LZWDecodeCompat: Not enough data at scanline %d (short %d bytes)",
                tif->tif_row, occ);
            return (0);
      }
      return (1);
}
#endif /* LZW_COMPAT */

/*
 * LZW Encoding.
 */

static int
LZWSetupEncode(TIFF* tif)
{
      LZWCodecState* sp = EncoderState(tif);
      static const char module[] = "LZWSetupEncode";

      assert(sp != NULL);
      sp->enc_hashtab = (hash_t*) _TIFFmalloc(HSIZE*sizeof (hash_t));
      if (sp->enc_hashtab == NULL) {
            TIFFErrorExt(tif->tif_clientdata, module, "No space for LZW hash table");
            return (0);
      }
      return (1);
}

/*
 * Reset encoding state at the start of a strip.
 */
static int
LZWPreEncode(TIFF* tif, tsample_t s)
{
      LZWCodecState *sp = EncoderState(tif);

      (void) s;
      assert(sp != NULL);
      sp->lzw_nbits = BITS_MIN;
      sp->lzw_maxcode = MAXCODE(BITS_MIN);
      sp->lzw_free_ent = CODE_FIRST;
      sp->lzw_nextbits = 0;
      sp->lzw_nextdata = 0;
      sp->enc_checkpoint = CHECK_GAP;
      sp->enc_ratio = 0;
      sp->enc_incount = 0;
      sp->enc_outcount = 0;
      /*
       * The 4 here insures there is space for 2 max-sized
       * codes in LZWEncode and LZWPostDecode.
       */
      sp->enc_rawlimit = tif->tif_rawdata + tif->tif_rawdatasize-1 - 4;
      cl_hash(sp);            /* clear hash table */
      sp->enc_oldcode = (hcode_t) -1;     /* generates CODE_CLEAR in LZWEncode */
      return (1);
}

#define     CALCRATIO(sp, rat) {                            \
      if (incount > 0x007fffff) { /* NB: shift will overflow */\
            rat = outcount >> 8;                      \
            rat = (rat == 0 ? 0x7fffffff : incount/rat);    \
      } else                                          \
            rat = (incount<<8) / outcount;                  \
}
#define     PutNextCode(op, c) {                            \
      nextdata = (nextdata << nbits) | c;             \
      nextbits += nbits;                              \
      *op++ = (unsigned char)(nextdata >> (nextbits-8));          \
      nextbits -= 8;                                  \
      if (nextbits >= 8) {                            \
            *op++ = (unsigned char)(nextdata >> (nextbits-8));    \
            nextbits -= 8;                            \
      }                                         \
      outcount += nbits;                              \
}

/*
 * Encode a chunk of pixels.
 *
 * Uses an open addressing double hashing (no chaining) on the 
 * prefix code/next character combination.  We do a variant of
 * Knuth's algorithm D (vol. 3, sec. 6.4) along with G. Knott's
 * relatively-prime secondary probe.  Here, the modular division
 * first probe is gives way to a faster exclusive-or manipulation. 
 * Also do block compression with an adaptive reset, whereby the
 * code table is cleared when the compression ratio decreases,
 * but after the table fills.  The variable-length output codes
 * are re-sized at this point, and a CODE_CLEAR is generated
 * for the decoder. 
 */
static int
LZWEncode(TIFF* tif, tidata_t bp, tsize_t cc, tsample_t s)
{
      register LZWCodecState *sp = EncoderState(tif);
      register long fcode;
      register hash_t *hp;
      register int h, c;
      hcode_t ent;
      long disp;
      long incount, outcount, checkpoint;
      long nextdata, nextbits;
      int free_ent, maxcode, nbits;
      tidata_t op, limit;

      (void) s;
      if (sp == NULL)
            return (0);
      /*
       * Load local state.
       */
      incount = sp->enc_incount;
      outcount = sp->enc_outcount;
      checkpoint = sp->enc_checkpoint;
      nextdata = sp->lzw_nextdata;
      nextbits = sp->lzw_nextbits;
      free_ent = sp->lzw_free_ent;
      maxcode = sp->lzw_maxcode;
      nbits = sp->lzw_nbits;
      op = tif->tif_rawcp;
      limit = sp->enc_rawlimit;
      ent = sp->enc_oldcode;

      if (ent == (hcode_t) -1 && cc > 0) {
            /*
             * NB: This is safe because it can only happen
             *     at the start of a strip where we know there
             *     is space in the data buffer.
             */
            PutNextCode(op, CODE_CLEAR);
            ent = *bp++; cc--; incount++;
      }
      while (cc > 0) {
            c = *bp++; cc--; incount++;
            fcode = ((long)c << BITS_MAX) + ent;
            h = (c << HSHIFT) ^ ent;      /* xor hashing */
#ifdef _WINDOWS
            /*
             * Check hash index for an overflow.
             */
            if (h >= HSIZE)
                  h -= HSIZE;
#endif
            hp = &sp->enc_hashtab[h];
            if (hp->hash == fcode) {
                  ent = hp->code;
                  continue;
            }
            if (hp->hash >= 0) {
                  /*
                   * Primary hash failed, check secondary hash.
                   */
                  disp = HSIZE - h;
                  if (h == 0)
                        disp = 1;
                  do {
                        /*
                         * Avoid pointer arithmetic 'cuz of
                         * wraparound problems with segments.
                         */
                        if ((h -= disp) < 0)
                              h += HSIZE;
                        hp = &sp->enc_hashtab[h];
                        if (hp->hash == fcode) {
                              ent = hp->code;
                              goto hit;
                        }
                  } while (hp->hash >= 0);
            }
            /*
             * New entry, emit code and add to table.
             */
            /*
             * Verify there is space in the buffer for the code
             * and any potential Clear code that might be emitted
             * below.  The value of limit is setup so that there
             * are at least 4 bytes free--room for 2 codes.
             */
            if (op > limit) {
                  tif->tif_rawcc = (tsize_t)(op - tif->tif_rawdata);
                  TIFFFlushData1(tif);
                  op = tif->tif_rawdata;
            }
            PutNextCode(op, ent);
            ent = c;
            hp->code = free_ent++;
            hp->hash = fcode;
            if (free_ent == CODE_MAX-1) {
                  /* table is full, emit clear code and reset */
                  cl_hash(sp);
                  sp->enc_ratio = 0;
                  incount = 0;
                  outcount = 0;
                  free_ent = CODE_FIRST;
                  PutNextCode(op, CODE_CLEAR);
                  nbits = BITS_MIN;
                  maxcode = MAXCODE(BITS_MIN);
            } else {
                  /*
                   * If the next entry is going to be too big for
                   * the code size, then increase it, if possible.
                   */
                  if (free_ent > maxcode) {
                        nbits++;
                        assert(nbits <= BITS_MAX);
                        maxcode = (int) MAXCODE(nbits);
                  } else if (incount >= checkpoint) {
                        long rat;
                        /*
                         * Check compression ratio and, if things seem
                         * to be slipping, clear the hash table and
                         * reset state.  The compression ratio is a
                         * 24+8-bit fractional number.
                         */
                        checkpoint = incount+CHECK_GAP;
                        CALCRATIO(sp, rat);
                        if (rat <= sp->enc_ratio) {
                              cl_hash(sp);
                              sp->enc_ratio = 0;
                              incount = 0;
                              outcount = 0;
                              free_ent = CODE_FIRST;
                              PutNextCode(op, CODE_CLEAR);
                              nbits = BITS_MIN;
                              maxcode = MAXCODE(BITS_MIN);
                        } else
                              sp->enc_ratio = rat;
                  }
            }
      hit:
            ;
      }

      /*
       * Restore global state.
       */
      sp->enc_incount = incount;
      sp->enc_outcount = outcount;
      sp->enc_checkpoint = checkpoint;
      sp->enc_oldcode = ent;
      sp->lzw_nextdata = nextdata;
      sp->lzw_nextbits = nextbits;
      sp->lzw_free_ent = free_ent;
      sp->lzw_maxcode = maxcode;
      sp->lzw_nbits = nbits;
      tif->tif_rawcp = op;
      return (1);
}

/*
 * Finish off an encoded strip by flushing the last
 * string and tacking on an End Of Information code.
 */
static int
LZWPostEncode(TIFF* tif)
{
      register LZWCodecState *sp = EncoderState(tif);
      tidata_t op = tif->tif_rawcp;
      long nextbits = sp->lzw_nextbits;
      long nextdata = sp->lzw_nextdata;
      long outcount = sp->enc_outcount;
      int nbits = sp->lzw_nbits;

      if (op > sp->enc_rawlimit) {
            tif->tif_rawcc = (tsize_t)(op - tif->tif_rawdata);
            TIFFFlushData1(tif);
            op = tif->tif_rawdata;
      }
      if (sp->enc_oldcode != (hcode_t) -1) {
            PutNextCode(op, sp->enc_oldcode);
            sp->enc_oldcode = (hcode_t) -1;
      }
      PutNextCode(op, CODE_EOI);
      if (nextbits > 0) 
            *op++ = (unsigned char)(nextdata << (8-nextbits));
      tif->tif_rawcc = (tsize_t)(op - tif->tif_rawdata);
      return (1);
}

/*
 * Reset encoding hash table.
 */
static void
cl_hash(LZWCodecState* sp)
{
      register hash_t *hp = &sp->enc_hashtab[HSIZE-1];
      register long i = HSIZE-8;

      do {
            i -= 8;
            hp[-7].hash = -1;
            hp[-6].hash = -1;
            hp[-5].hash = -1;
            hp[-4].hash = -1;
            hp[-3].hash = -1;
            hp[-2].hash = -1;
            hp[-1].hash = -1;
            hp[ 0].hash = -1;
            hp -= 8;
      } while (i >= 0);
      for (i += 8; i > 0; i--, hp--)
            hp->hash = -1;
}

static void
LZWCleanup(TIFF* tif)
{
      (void)TIFFPredictorCleanup(tif);

      assert(tif->tif_data != 0);

      if (DecoderState(tif)->dec_codetab)
            _TIFFfree(DecoderState(tif)->dec_codetab);

      if (EncoderState(tif)->enc_hashtab)
            _TIFFfree(EncoderState(tif)->enc_hashtab);

      _TIFFfree(tif->tif_data);
      tif->tif_data = NULL;

      _TIFFSetDefaultCompressionState(tif);
}

int
TIFFInitLZW(TIFF* tif, int scheme)
{
      assert(scheme == COMPRESSION_LZW);
      /*
       * Allocate state block so tag methods have storage to record values.
       */
      tif->tif_data = (tidata_t) _TIFFmalloc(sizeof (LZWCodecState));
      if (tif->tif_data == NULL)
            goto bad;
      DecoderState(tif)->dec_codetab = NULL;
      DecoderState(tif)->dec_decode = NULL;
      EncoderState(tif)->enc_hashtab = NULL;
        LZWState(tif)->rw_mode = tif->tif_mode;

      /*
       * Install codec methods.
       */
      tif->tif_setupdecode = LZWSetupDecode;
      tif->tif_predecode = LZWPreDecode;
      tif->tif_decoderow = LZWDecode;
      tif->tif_decodestrip = LZWDecode;
      tif->tif_decodetile = LZWDecode;
      tif->tif_setupencode = LZWSetupEncode;
      tif->tif_preencode = LZWPreEncode;
      tif->tif_postencode = LZWPostEncode;
      tif->tif_encoderow = LZWEncode;
      tif->tif_encodestrip = LZWEncode;
      tif->tif_encodetile = LZWEncode;
      tif->tif_cleanup = LZWCleanup;
      /*
       * Setup predictor setup.
       */
      (void) TIFFPredictorInit(tif);
      return (1);
bad:
      TIFFErrorExt(tif->tif_clientdata, "TIFFInitLZW", 
                 "No space for LZW state block");
      return (0);
}

/*
 * Copyright (c) 1985, 1986 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * James A. Woods, derived from original work by Spencer Thomas
 * and Joseph Orost.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#endif /* LZW_SUPPORT */

/* vim: set ts=8 sts=8 sw=8 noet: */

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