/*
 * base64 [-e|-d]
 *
 * -e specifies encoding, -d decoding.
 */

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>

extern const char *__progname;

static char encoding[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static void encode(void)
{
 unsigned long int buf;
 int c;
 int n;
 int ol;

 n = 0;
 ol = 0;
 while (1)
  { c = getchar();
    if (c == EOF) break;
    buf = (buf << 8) | c;
    n ++;
    if (n > 2)
     { for (n=18;n>=0;n-=6) putchar(encoding[(buf>>n)&0x3f]);
       ol += 4;
       if (ol > 60)
	{ putchar('\n');
	  ol = 0;
	}
       n = 0;
     }
  }
 switch (n)
  { case 0:
       break;
    case 1:
       putchar(encoding[(buf>>2)&0x3f]);
       putchar(encoding[(buf<<4)&0x30]);
       printf("==");
       ol += 4;
       break;
    case 2:
       putchar(encoding[(buf>>10)&0x3f]);
       putchar(encoding[(buf>>4)&0x3f]);
       putchar(encoding[(buf<<2)&0x3c]);
       putchar('=');
       ol += 4;
       break;
  }
 if (ol > 0) putchar('\n');
}

static void decode(void)
{
 unsigned long int buf;
 int n;
 int c;
 char *ep;

 n = 0;
 while (1)
  { c = getchar();
    if (c == EOF)
     { if (n) fprintf(stderr,"%s: warning: unexpected EOF\n",__progname);
       break;
     }
    if (c == '=')
     { switch (n)
	{ case 0:
	     break;
	  case 1:
	     fprintf(stderr,"%s: warning: invalid encoding: = at invalid place\n",__progname);
	     break;
	  case 2:
	     putchar((buf>>4)&0xff);
	     break;
	  case 3:
	     putchar((buf>>10)&0xff);
	     putchar((buf>>2)&0xff);
	     break;
	}
       break;
     }
    ep = index(&encoding[0],c);
    if (! ep) continue;
    buf = (buf << 6) | (ep - &encoding[0]);
    n ++;
    if (n > 3)
     { putchar((buf>>16)&0xff);
       putchar((buf>>8)&0xff);
       putchar(buf&0xff);
       n = 0;
     }
  }
}

int main(int, char **);
int main(int ac, char **av)
{
 if (0)
  {
usage:;
    fprintf(stderr,"Usage: %s [-e|-d]\n",__progname);
    exit(1);
  }
 if (ac != 2) goto usage;
      if (!strcmp(av[1],"-e")) encode();
 else if (!strcmp(av[1],"-d")) decode();
 else goto usage;
 exit(0);
}