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/*

 * LZW decoder

 * Copyright (c) 2003 Fabrice Bellard

 * Copyright (c) 2006 Konstantin Shishkov

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * FFmpeg is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file

 * @brief LZW decoding routines

 * @author Fabrice Bellard

 * @author modified for use in TIFF by Konstantin Shishkov

 */

#include "avcodec.h"

#include "lzw.h"

#include "libavutil/mem.h"

#define LZW_MAXBITS                 12

#define LZW_SIZTABLE                (1<

static const uint16_t mask[17] =

{

    0x0000, 0x0001, 0x0003, 0x0007,

    0x000F, 0x001F, 0x003F, 0x007F,

    0x00FF, 0x01FF, 0x03FF, 0x07FF,

    0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF

};

struct LZWState {

    const uint8_t *pbuf, *ebuf;

    int bbits;

    unsigned int bbuf;

    int mode;                   ///< Decoder mode

    int cursize;                ///< The current code size

    int curmask;

    int codesize;

    int clear_code;

    int end_code;

    int newcodes;               ///< First available code

    int top_slot;               ///< Highest code for current size

    int extra_slot;

    int slot;                   ///< Last read code

    int fc, oc;

    uint8_t *sp;

    uint8_t stack[LZW_SIZTABLE];

    uint8_t suffix[LZW_SIZTABLE];

    uint16_t prefix[LZW_SIZTABLE];

    int bs;                     ///< current buffer size for GIF

};

/* get one code from stream */

static int lzw_get_code(struct LZWState * s)

{

    int c;

    if(s->mode == FF_LZW_GIF) {

        while (s->bbits < s->cursize) {

            if (!s->bs) {

                s->bs = *s->pbuf++;

            }

            s->bbuf |= (*s->pbuf++) << s->bbits;

            s->bbits += 8;

            s->bs--;

        }

        c = s->bbuf;

        s->bbuf >>= s->cursize;

    } else { // TIFF

        while (s->bbits < s->cursize) {

            s->bbuf = (s->bbuf << 8) | (*s->pbuf++);

            s->bbits += 8;

        }

        c = s->bbuf >> (s->bbits - s->cursize);

    }

    s->bbits -= s->cursize;

    return c & s->curmask;

}

void ff_lzw_decode_tail(LZWState *p)

{

    struct LZWState *s = (struct LZWState *)p;

    if(s->mode == FF_LZW_GIF) {

        while (s->bs > 0) {

            if (s->bs >= s->ebuf - s->pbuf) {

                s->pbuf = s->ebuf;

                break;

            } else {

                s->pbuf += s->bs;

                s->bs = *s->pbuf++;

            }

        }

    }else

        s->pbuf= s->ebuf;

}

av_cold void ff_lzw_decode_open(LZWState **p)

{

    *p = av_mallocz(sizeof(struct LZWState));

}

av_cold void ff_lzw_decode_close(LZWState **p)

{

    av_freep(p);

}

/**

 * Initialize LZW decoder

 * @param p LZW context

 * @param csize initial code size in bits

 * @param buf input data

 * @param buf_size input data size

 * @param mode decoder working mode - either GIF or TIFF

 */

int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)

{

    struct LZWState *s = (struct LZWState *)p;

    if(csize < 1 || csize >= LZW_MAXBITS)

        return -1;

    /* read buffer */

    s->pbuf = buf;

    s->ebuf = s->pbuf + buf_size;

    s->bbuf = 0;

    s->bbits = 0;

    s->bs = 0;

    /* decoder */

    s->codesize = csize;

    s->cursize = s->codesize + 1;

    s->curmask = mask[s->cursize];

    s->top_slot = 1 << s->cursize;

    s->clear_code = 1 << s->codesize;

    s->end_code = s->clear_code + 1;

    s->slot = s->newcodes = s->clear_code + 2;

    s->oc = s->fc = -1;

    s->sp = s->stack;

    s->mode = mode;

    s->extra_slot = s->mode == FF_LZW_TIFF;

    return 0;

}

/**

 * Decode given number of bytes

 * NOTE: the algorithm here is inspired from the LZW GIF decoder

 *  written by Steven A. Bennett in 1987.

 *

 * @param p LZW context

 * @param buf output buffer

 * @param len number of bytes to decode

 * @return number of bytes decoded

 */

int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){

    int l, c, code, oc, fc;

    uint8_t *sp;

    struct LZWState *s = (struct LZWState *)p;

    if (s->end_code < 0)

        return 0;

    l = len;

    sp = s->sp;

    oc = s->oc;

    fc = s->fc;

    for (;;) {

        while (sp > s->stack) {

            *buf++ = *(--sp);

            if ((--l) == 0)

                goto the_end;

        }

        if (s->ebuf < s->pbuf) {

            av_log(NULL, AV_LOG_ERROR, "lzw overread\n");

            goto the_end;

        }

        c = lzw_get_code(s);

        if (c == s->end_code) {

            break;

        } else if (c == s->clear_code) {

            s->cursize = s->codesize + 1;

            s->curmask = mask[s->cursize];

            s->slot = s->newcodes;

            s->top_slot = 1 << s->cursize;

            fc= oc= -1;

        } else {

            code = c;

            if (code == s->slot && fc>=0) {

                *sp++ = fc;

                code = oc;

            }else if(code >= s->slot)

                break;

            while (code >= s->newcodes) {

                *sp++ = s->suffix[code];

                code = s->prefix[code];

            }

            *sp++ = code;

            if (s->slot < s->top_slot && oc>=0) {

                s->suffix[s->slot] = code;

                s->prefix[s->slot++] = oc;

            }

            fc = code;

            oc = c;

            if (s->slot >= s->top_slot - s->extra_slot) {

                if (s->cursize < LZW_MAXBITS) {

                    s->top_slot <<= 1;

                    s->curmask = mask[++s->cursize];

                }

            }

        }

    }

    s->end_code = -1;

  the_end:

    s->sp = sp;

    s->oc = oc;

    s->fc = fc;

    return len - l;

}