btoa.c

和Unix的compress/uncompress兼容的压缩/解压算法16位程序

/* btoa: version 4.0
 * stream filter to change 8 bit bytes into printable ascii
 * computes the number of bytes, and three kinds of simple checksums
 * incoming bytes are collected into 32-bit words, then printed in base 85
 *  exp(85,5) > exp(2,32)
 * the ASCII characters used are between '!' and 'u'
 * 'z' encodes 32-bit zero; 'x' is used to mark the end of encoded data.
 *
 *  Paul Rutter		Joe Orost
 *  philabs!per		petsd!joe
 *
 *  WARNING: this version is not compatible with the original as sent out
 *  on the net.  The original encoded from ' ' to 't'; which cause problems
 *  with some mailers (stripping off trailing blanks).
 */
/* DjG - Don Gloistein
 *  Made some changes to compile with msdos/16 bit compilers. Some compilers
 *  do not make the same assumptions on promoting an integer to long constant.
 *  Msdos computers support a text and binary mode file open. Stdin/stdout are
 *  defaulted to text streams. Included SETMODE for those systems. If compiled
 *  without any defines, it will default to the stock unix version.
 */

#include <stdio.h>

#ifdef MSC
#include <fcntl.h>
#include <io.h>
#define SETMODE(x) setmode(fileno((x)),O_BINARY)
#endif

#ifdef MWC_ATARI
#define SETMODE(x) ((x)->_ff &= ~(_FASCII))
#endif
/* following take care of unix systems */
#ifndef SETMODE
#define SETMODE(x)
#endif

#define reg register

#define MAXPERLINE 78

long int Ceor = 0L;
long int Csum = 0L;
long int Crot = 0L;

long int ccount = 0L;
int bcount = 0;
long int word = 0L;

#define EN(c)	(int) ((c) + '!')

encode(c)
  reg c;
{
  Ceor ^= c;
  Csum += c;
  Csum += 1;
  if ((Crot & 0x80000000)) {
    Crot <<= 1;
    Crot += 1;
  } else {
    Crot <<= 1;
  }
  Crot += c;

  word <<= 8;
  word |= c;
  if (bcount == 3) {
    wordout(word);
    bcount = 0;
  } else {
    bcount += 1;
  }
}

wordout(word)
  reg long int word;
{
  if (word == 0) {
    charout('z');
  } else {
    reg int tmp = 0;

    if(word < 0L) {  /* Because some don't support unsigned long */
      tmp = 32;
      word = word - (85L * 85L * 85L * 85L * 32L);
    }
    if(word < 0L) {
      tmp = 64;
      word = word - (85L * 85L * 85L * 85L * 32L);
    }
    charout(EN((word / (85L * 85L * 85L * 85L)) + tmp));
    word %= (85L * 85L * 85L * 85L);
    charout(EN(word / (85L * 85L * 85L)));
    word %= (85L * 85L * 85L);
    charout(EN(word / (85L * 85L)));
    word %= (85L * 85L);
    charout(EN(word / 85L));
    word %= 85L;
    charout(EN(word));
  }
}

charout(c) {
  putchar(c);
  ccount += 1;
  if (ccount == MAXPERLINE) {
    putchar('\n');
    ccount = 0;
  }
}

main(argc,argv)
  char **argv;
{
  reg c;
  reg long int n;

  if (argc != 1) {
    fprintf(stderr,"bad args to %s\n", argv[0]);
    exit(2);
  }
  SETMODE(stdin);
  SETMODE(stdout);
  printf("xbtoa Begin\n");
  n = 0;
  while ((c = getchar()) != EOF) {
    encode(c);
    n += 1;
  }
  while (bcount != 0) {
    encode(0);
  }
  /* n is written twice as crude cross check*/
  printf("\nxbtoa End N %ld %lx E %lx S %lx R %lx\n", n, n, Ceor, Csum, Crot);
  exit(0);
}