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[wxWidgets.git] / src / tiff / libtiff / tif_lzw.c

/* $Id$ */

/*
 * 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: */