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comp_text.c

/*
 * Copyright (C) 2001, 2002, and 2003  Roy Keene
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 *      email: dact@rkeene.org
 */


#include "dact.h"
#include "comp_text.h"
#include "buffer.h"
#include <stdio.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif


/*
      mode        - DACT_MODE_COMPR or DACT_MODE_DECMP
                      Determine whether to compress or decompress.
      prev_block  - Previous (uncompressed) block.
      curr_block  - The data to be compressed.
      out_block   - Where to put data after compression.
      blk_size    - Size of prev_block and curr_block.
*/

#if defined(USE_MODULES) && defined(AS_MODULE)
#include "module.h"
uint32_t DC_NUM=3;
uint32_t DC_TYPE=DACT_MOD_TYPE_COMP;
void *DC_ALGO=comp_text_algo;
char *DC_NAME="Text Compression (MOD)";
#endif

int comp_text_algo(int mode, unsigned char *prev_block, unsigned char *curr_block, char *out_block, int blk_size, int bufsize) {
      switch(mode) {
            case DACT_MODE_COMPR:
                  return(comp_text_compress(prev_block, curr_block, out_block, blk_size, bufsize));
                  break; /* Heh */
            case DACT_MODE_DECMP:
                  return(comp_text_decompress(prev_block, curr_block, out_block, blk_size, bufsize));
                  break;
            default:
                  printf("Unsupported mode: %i\n", mode);
                  return(-1);
      }
}

int comp_text_compress(unsigned char *prev_block, unsigned char *curr_block, char *out_block, int blk_size, int bufsize) {
      unsigned char low_byte=255, high_byte=0;
      unsigned char byte_buf;
      unsigned int range;
      int i,x=0,y;


      bit_buffer_purge();

      for (i=0;i<blk_size;i++) {
            if (((unsigned char) curr_block[i])<low_byte) low_byte=curr_block[i];
            if (((unsigned char) curr_block[i])>high_byte) high_byte=curr_block[i];
      }

      range=(unsigned int) (high_byte-low_byte);

      out_block[x++]=low_byte;
      out_block[x++]=high_byte;

      if (range==0)
            return(2);

      for (y=1;y<=8;y++)
            if ((range>>y)==0) break;
      if (y==8) return(-1);

      for (i=0;i<blk_size;i++) {
            byte_buf=(unsigned char) (curr_block[i]-low_byte);
/*
            if ((byte_buf>>y)==1) {
                  return(-1);
            }
*/
            bit_buffer_write(byte_buf,y);

            while (bit_buffer_size()>=8) {
                  out_block[x++]=bit_buffer_read(8);
            }
      }
/*          Remove any less-than-one-byte data */
      if ((i=bit_buffer_size())!=0) {
            out_block[x++]=(bit_buffer_read(i)<<(8-i));
      }

      return(x);
}

int comp_text_decompress(unsigned char *prev_block, unsigned char *curr_block, char *out_block, int blk_size, int bufsize) {
      unsigned char high_byte, low_byte;
      unsigned int range;
      int i=0,x=0,y;
      
      low_byte=curr_block[x++];
      high_byte=curr_block[x++];
      range=(unsigned int) (high_byte-low_byte);

      if (range==0) {
            memset(out_block, low_byte, bufsize);
            return(bufsize);
      }
        for (y=1;y<=8;y++)
                if ((range>>y)==0) break;

      bit_buffer_purge();

      while (1) {
            if (bit_buffer_size()<y) bit_buffer_write((unsigned char) curr_block[x++],8);
            out_block[i++]=(bit_buffer_read(y)+low_byte);
            if ((x==blk_size) && (bit_buffer_size()<y)) break;
            if (i>=(bufsize)) break;
      }

      return(i);
}

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