Path: news.uiowa.edu!chi-news.cic.net!nntp.coast.net!news2.acs.oakland.edu!newshub.gmr.com!hobbes.tad.eds.com!maverick.tad.eds.com!news-admin@tad.eds.com
From: Erick Wagner <wagnere@netcom.com>
Newsgroups: comp.sys.apple2.comm
Subject: Re: BASE64 Compression
Date: 26 Feb 1996 19:13:41 GMT
Organization: PRC
Lines: 167
Message-ID: <4gt0p5$p2p@maverick.tad.eds.com>
References: <billg-0902960738520001@betty-p04.netinfo.com.au> <bd70339@pro-nsdapple.cts.com> <4ft19a$15j@maverick.tad.eds.com> <4gqrg1$g2q@madeline.INS.CWRU.Edu>
NNTP-Posting-Host: 148.94.8.235
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 1.22 (Windows; I; 16bit)

gj380@cleveland.Freenet.Edu (Adalbert Goertz) wrote:
>
>it would be nice if someone would write a base64 decompressor.

I'm not sure who the original author was but here's some base64
source I snagged off the 'net (after using one of the search engines).

I've used it a couple of times on the PC and it seems work okay, but
I never come across base64-encoded data very often to say that this
program works as it should...

The only changes I've made to this source has been in the way of
comments (especially usage notes).

Good luck

Erick

/*
  BASE64.C

  PURPOSE
  
    Decode BASE64 encoded data

  NOTES

    This program expects to receive a BASE-64 encoded data stream
    via "stdin" and sends the decoded data stream to "stdout"

      pgm < inputfile > outputfile

    After using this program and depending on specific OS requirements,
    you may need to rename the file with the proper file extension, 
    set the proper file type (and auxiliary file type if applicable),
    or perform additional manipulations before the new file will be
    recognized in the target environment.
*/

#include <stdio.h>
  /* getchar(), putchar() */
#include <stdlib.h>
  /* exit() */

static unsigned char b64_bin[256]; /* => 0..63, pad=64, inv=65, else ign 
*/


/*
  -------------
  init_b64bin()
  -------------

  setup B64 (ascii) => binary table
*/
static void init_b64bin(void)
  {
  int i,j;

  for(i = 0; i <= 32; i++) b64_bin[i] = 66;       /* ignore controls */
  for(i = 33; i < 127; i++) b64_bin[i] = 65;      /* printable => inv */
  for(i = 127; i <= 160; i++) b64_bin[i] = 66;    /* ignore controls */
  for(i = 161; i < 256; i++) b64_bin[i] = 65;     /* printable => inv */

  j = 0;
  for(i = 'A'; i <= 'Z'; i++, j++) b64_bin[i] = j;
  for(i = 'a'; i <= 'z'; i++, j++) b64_bin[i] = j;
  for(i = '0'; i <= '9'; i++, j++) b64_bin[i] = j;
  b64_bin['+'] = j++;
  b64_bin['/'] = j++;

  b64_bin['='] = 64;
  }


/*
  ------------
  GNC_b64bin()
  ------------

  get next 6-bit group, or pad
*/
static int GNC_b64bin(unsigned int *ip)
  {
  int c;

  do
    {
    c = getchar();
    if (c == EOF) return EOF;
    *ip = b64_bin[c & 0xFF];
    } while(*ip > 65);

  return 0;
  }


/*
  -----------
  do_decode()
  -----------

  decode => stdout
*/
static void do_decode(void)
  {
  int /*logical*/ done;
  unsigned int v6;
  unsigned int v24;               /* room for >= 24 bits */

  #define ERROR exit(2)

  done = 0;

  while(GNC_b64bin(&v6) != EOF)
    {
    if(done) ERROR;         /* bytes following pad */

    if(v6 > 63) ERROR;
    v24 = v6;
    if(GNC_b64bin(&v6) == EOF) ERROR;
    if(v6 > 63) ERROR;
    v24 = (v24 << 6) | v6;

    putchar((v24 >> (2*6-8)) & 0xFF);

    if(GNC_b64bin(&v6) == EOF) ERROR;
    if(v6 > 64) ERROR;      /* invalid */
    if(v6 == 64)
      {                  /* pad after 1 char */
      done = 1;
      if(GNC_b64bin(&v6) == EOF) ERROR;
      if(v6 != 64) ERROR;
      }
    else
      {
      v24 = (v24 << 6) | v6;

      putchar((v24 >> (3*6-16)) & 0xFF);

      if(GNC_b64bin(&v6) == EOF) ERROR;
      if(v6 > 64) ERROR;      /* invalid */

      if(v6 == 64)
        {          /* pad after 2 char */
        done = 1;
        }
      else
        {
        putchar(((v24 << 6) | v6) & 0xFF);
        }
      }
    }

  exit(0);
  }


int main(int argc, char **argv)
  {
  init_b64bin();
  do_decode();

  return 0;
  }