Shell Programming and Scripting

$ cat mysrc/base64dec.c

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

static int i, o ;
static int ostate = 0 ;

static void p_putchar( int c ){
//fprintf(stderr,"p_putchar(%d=%c)\n",c,c);
  if ( EOF == putchar( c )){
    if ( ferror( stdout )){
      perror( "base64dec: stdout" );
      exit( 1 );
     }

    exit( 0 );
   }
 }

static void newbits( int b ){
//fprintf(stderr,"newbits(%d), ostate %d, o %d, i %d=%c\n",b,ostate,o,i,i);
  switch ( ostate ){
   case 0:
    o = b ;
    ostate = 6 ;
    return ;
   case 6:
    p_putchar( ( o << 2 ) | ( b >> 4 ) );
    o = b & 15 ;
    ostate = 4 ;
    return ;
   case 4:
    p_putchar( ( o << 4 ) | ( b >> 2 ));
    o = b & 3 ;
    ostate = 2 ;
    return ;
   default:
    p_putchar( ( o << 6 ) | b );
    ostate = 0 ;
    return ;
   }
 }

int main( int argc, char **argv ){

  int v = 0 ;

  if ( argc > 1
    && !strcmp( argv[1], "-v" )){
      v = 1 ;
   }

  while ( EOF != ( i = getchar())){
    if ( i > 'z' ){
      continue ;
     }

    if ( i < '+' ){
      continue ;
     }

    if ( i > 'Z' ){
      if ( i >= 'a' ){
        newbits( i - 'a' + 26 );
       }
      continue ;
     }

    if ( i >= 'A' ){
      newbits( i - 'A' );
      continue ;
     }   

    if ( i > '9' ){
      continue ;
     }   

    if ( i >= '0' ){
      newbits( i - '0' + 52 );
      continue ;
     }   

    if ( i == '/' ){
      newbits( 63 );
      continue ;
     }   

    if ( i == '+' ){
      newbits( 62 );
     }   
   } /* end while getchar */

  if ( ferror( stdin )){
    perror( "base64dec: stdin" );
    exit( 1 );
   }

  if ( ostate && v ){
    fprintf( stderr,
"\nbase64dec: Warning: %d bits =%d left at EOF.\n",
      ostate, o );
    exit( 2 );
   }

  exit( 0 );
 }