/*
  * 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"
 
 #define LZW_MAXBITS                 12
 #define LZW_SIZTABLE                (1<<LZW_MAXBITS)
 
 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;

 }
 

 const uint8_t* ff_lzw_cur_ptr(LZWState *p)

 {
     return ((struct LZWState*)p)->pbuf;
 }
 
 void ff_lzw_decode_tail(LZWState *p)
 {
     struct LZWState *s = (struct LZWState *)p;

 
     if(s->mode == FF_LZW_GIF) {
         while(s->pbuf < s->ebuf && s->bs>0){
             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;
         }

         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;
 }