huff.cpp

压缩算法的C语言源程序

/*
   huff.cpp
   Huffman coding examples
*/
#include <stdio.h>
#include <compress.h>

int main(int argc,char *argv[])
{
   STREAM *in, *out;
   int compress;

   if(argc != 4) {
      // display usage
printusage:
      fprintf(stderr,"USAGE: HUFF [-c|d] <infile> <outfile>\n");
      fprintf(stderr,"Where -c is compress, -d is decompress\n");
      return 1;
   }

   // test flag if it is -c or -d
   if(argv[1][0] == '-') {
      if(argv[1][1] == 'c') compress = 1;
      else if(argv[1][1] == 'd') compress = 0;
      else goto printusage;
   } else goto printusage;

   in = stream_open(argv[2],"rb"); // open input file
   if(!in) {
      fprintf(stderr,"Can't open file `%s'.\n",argv[2]);
      return 1;
   }
   out = stream_open(argv[3],"wb"); // open input file
   if(!in) {
      stream_close(in);
      fprintf(stderr,"Can't open file `%s'.\n",argv[3]);
      return 1;
   }

   HuffTable tab[257]; // make a table of 257 entries since there are 256
                       // characters in a byte + 1 EOF code
   int i, ch;
   if(compress) { // if compressing
      for(i = 0; i < 257; i++) { // initialize the huffman table
         tab[i].code = i;
         tab[i].len = 0;
      }

      // build a table of frequency counts
      while((ch = stream_getc(in)) != EOF) tab[ch].len++;
      tab[256].len = 1; // EOF code has a count of 1
      CalculateMinimumRedundancy(tab,257); // calculate minimum bits to encode
      BuildHuffTable(tab,257); // Generate the huff codes

      WriteHuffmanHeader(out,tab,257,0); // write huffman header
      stream_seek(in,0L,SEEK_SET); // rewind stream
      while((ch = stream_getc(in)) != EOF)
         WriteHuffmanCode(out,tab[ch]); // Write huffman code

      WriteHuffmanCode(out,tab[256]); // always write EOF code
      stream_flush_write_bufferr(out); // flush output buffer
   } else { // if decomrpession
      // read the huffman header, we assume that the header is always 257 entries
      // so we pass NULL to the nLit parameter
      ReadHuffmanHeader(in,tab,NULL,NULL,NULL);

      HuffLookup *lookup;  // lookup table for decompress

      lookup = BuildHuffmanLookupTable(tab,257); // generate lookup table
      if(!lookup) {
         fprintf(stderr,"Out of memory.\n");
         stream_close(in);
         stream_close(out);
         return 1;
      }

      ch = 0;
      for(;;) {
         ch = FetchHuffmanCode(in,lookup); // fetch code
         if(ch == 256 || stream_eof(in)) break;
         stream_putc(ch,out);  // output code
      }
   }

   stream_close(in);
   stream_close(out);

   return 0;
}