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/*
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 * LZW decoder
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 * Copyright (c) 2003 Fabrice Bellard
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 * Copyright (c) 2006 Konstantin Shishkov
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/**
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 * @file
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 * @brief LZW decoding routines
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 * @author Fabrice Bellard
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 * Modified for use in TIFF by Konstantin Shishkov
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 */
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#include "avcodec.h"
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#include "lzw.h"
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#define LZW_MAXBITS                 12
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#define LZW_SIZTABLE                (1<<LZW_MAXBITS)
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static const uint16_t mask[17] =
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{
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    0x0000, 0x0001, 0x0003, 0x0007,
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    0x000F, 0x001F, 0x003F, 0x007F,
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    0x00FF, 0x01FF, 0x03FF, 0x07FF,
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    0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF
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};
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struct LZWState {
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    const uint8_t *pbuf, *ebuf;
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    int bbits;
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    unsigned int bbuf;
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    int mode;                   ///< Decoder mode
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    int cursize;                ///< The current code size
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    int curmask;
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    int codesize;
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    int clear_code;
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    int end_code;
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    int newcodes;               ///< First available code
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    int top_slot;               ///< Highest code for current size
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    int extra_slot;
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    int slot;                   ///< Last read code
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    int fc, oc;
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    uint8_t *sp;
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    uint8_t stack[LZW_SIZTABLE];
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    uint8_t suffix[LZW_SIZTABLE];
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    uint16_t prefix[LZW_SIZTABLE];
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    int bs;                     ///< current buffer size for GIF
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};
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/* get one code from stream */
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static int lzw_get_code(struct LZWState * s)
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{
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    int c;
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    if(s->mode == FF_LZW_GIF) {
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        while (s->bbits < s->cursize) {
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            if (!s->bs) {
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                s->bs = *s->pbuf++;
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            }
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            s->bbuf |= (*s->pbuf++) << s->bbits;
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            s->bbits += 8;
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            s->bs--;
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        }
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        c = s->bbuf;
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        s->bbuf >>= s->cursize;
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    } else { // TIFF
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        while (s->bbits < s->cursize) {
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            s->bbuf = (s->bbuf << 8) | (*s->pbuf++);
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            s->bbits += 8;
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        }
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        c = s->bbuf >> (s->bbits - s->cursize);
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    }
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    s->bbits -= s->cursize;
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    return c & s->curmask;
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}
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const uint8_t* ff_lzw_cur_ptr(LZWState *p)
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{
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    return ((struct LZWState*)p)->pbuf;
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}
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void ff_lzw_decode_tail(LZWState *p)
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{
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    struct LZWState *s = (struct LZWState *)p;
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    if(s->mode == FF_LZW_GIF) {
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        while(s->pbuf < s->ebuf && s->bs>0){
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            s->pbuf += s->bs;
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            s->bs = *s->pbuf++;
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        }
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    }else
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        s->pbuf= s->ebuf;
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}
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av_cold void ff_lzw_decode_open(LZWState **p)
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{
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    *p = av_mallocz(sizeof(struct LZWState));
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}
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av_cold void ff_lzw_decode_close(LZWState **p)
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{
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    av_freep(p);
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}
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/**
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 * Initialize LZW decoder
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 * @param p LZW context
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 * @param csize initial code size in bits
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 * @param buf input data
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 * @param buf_size input data size
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 * @param mode decoder working mode - either GIF or TIFF
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 */
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int ff_lzw_decode_init(LZWState *p, int csize, const uint8_t *buf, int buf_size, int mode)
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{
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    struct LZWState *s = (struct LZWState *)p;
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    if(csize < 1 || csize >= LZW_MAXBITS)
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        return -1;
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    /* read buffer */
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    s->pbuf = buf;
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    s->ebuf = s->pbuf + buf_size;
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    s->bbuf = 0;
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    s->bbits = 0;
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    s->bs = 0;
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    /* decoder */
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    s->codesize = csize;
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    s->cursize = s->codesize + 1;
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    s->curmask = mask[s->cursize];
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    s->top_slot = 1 << s->cursize;
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    s->clear_code = 1 << s->codesize;
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    s->end_code = s->clear_code + 1;
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    s->slot = s->newcodes = s->clear_code + 2;
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    s->oc = s->fc = -1;
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    s->sp = s->stack;
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    s->mode = mode;
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    s->extra_slot = s->mode == FF_LZW_TIFF;
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    return 0;
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}
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/**
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 * Decode given number of bytes
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 * NOTE: the algorithm here is inspired from the LZW GIF decoder
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 *  written by Steven A. Bennett in 1987.
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 *
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 * @param p LZW context
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 * @param buf output buffer
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 * @param len number of bytes to decode
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 * @return number of bytes decoded
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 */
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int ff_lzw_decode(LZWState *p, uint8_t *buf, int len){
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    int l, c, code, oc, fc;
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    uint8_t *sp;
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    struct LZWState *s = (struct LZWState *)p;
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    if (s->end_code < 0)
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        return 0;
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    l = len;
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    sp = s->sp;
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    oc = s->oc;
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    fc = s->fc;
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    for (;;) {
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        while (sp > s->stack) {
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            *buf++ = *(--sp);
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            if ((--l) == 0)
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                goto the_end;
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        }
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        c = lzw_get_code(s);
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        if (c == s->end_code) {
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            break;
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        } else if (c == s->clear_code) {
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            s->cursize = s->codesize + 1;
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            s->curmask = mask[s->cursize];
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            s->slot = s->newcodes;
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            s->top_slot = 1 << s->cursize;
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            fc= oc= -1;
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        } else {
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            code = c;
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            if (code == s->slot && fc>=0) {
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                *sp++ = fc;
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                code = oc;
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            }else if(code >= s->slot)
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                break;
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            while (code >= s->newcodes) {
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                *sp++ = s->suffix[code];
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                code = s->prefix[code];
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            }
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            *sp++ = code;
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            if (s->slot < s->top_slot && oc>=0) {
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                s->suffix[s->slot] = code;
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                s->prefix[s->slot++] = oc;
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            }
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            fc = code;
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            oc = c;
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            if (s->slot >= s->top_slot - s->extra_slot) {
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                if (s->cursize < LZW_MAXBITS) {
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                    s->top_slot <<= 1;
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                    s->curmask = mask[++s->cursize];
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                }
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            }
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        }
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    }
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    s->end_code = -1;
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  the_end:
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    s->sp = sp;
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    s->oc = oc;
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    s->fc = fc;
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    return len - l;
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}