btoa.c

des算法实现源码

/* 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).
 */
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#if defined(__msdos) || defined(__MSDOS__)
#include <fcntl.h>	/* for setmode O_BINARY */
#endif

#define reg register

#define MAXPERLINE 78

#if defined(__msdos) || defined(__MSDOS__)
typedef  long s32;
#else
typedef  int s32;
#endif

s32 Ceor = 0;
s32 Csum = 0;
s32 Crot = 0;

s32 ccount = 0;
s32 bcount = 0;
s32 word;

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

void charout(c) 
  int c;
{

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

void wordout(word) 
  reg s32 word;
{
  if (word == 0) {
    charout('z');
  } else {
    reg int tmp = 0;
    
    if(word < 0) {	/* Because some don't support unsigned long */
      tmp = 32;
      word = word - ((s32)85 * 85 * 85 * 85 * 32);
    }
    if(word < 0) {
      tmp = 64;
      word = word - ((s32)85 * 85 * 85 * 85 * 32);
    }
    charout(EN((word / ((long)85 * 85 * 85 * 85)) + tmp));
    word %= ((s32)85 * 85 * 85 * 85);
    charout(EN(word / ((long)85 * 85 * 85)));
    word %= ((s32)85 * 85 * 85);
    charout(EN(word / (85 * 85)));
    word %= (85 * 85);
    charout(EN(word / 85));
    word %= 85;
    charout(EN(word));
  }
}


void 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;
  }
}

int main(argc,argv) 
  int argc;
  char **argv;
{
  reg c;
  reg s32 n;

  if (argc != 1) {
    fprintf(stderr,"bad args to %s\n", argv[0]);
    exit(2);
  }
#if defined(__msdos) || defined(__MSDOS__)
  setmode(0, O_BINARY);
#endif
  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);
}