static void decodeblock( unsigned char *in, unsigned char *out )
{
    out[ 0 ] = (unsigned char ) (in[0] << 2 | in[1] >> 4);
    out[ 1 ] = (unsigned char ) (in[1] << 4 | in[2] >> 2);
    out[ 2 ] = (unsigned char ) (((in[2] << 6) & 0xc0) | in[3]);
}
static int decode( FILE *infile, FILE *outfile )
{
    int retcode = 0;
    unsigned char in[4];
    unsigned char out[3];
    int v;
    int i, len;

    *in = (unsigned char) 0;
    *out = (unsigned char) 0;
    while( feof( infile ) == 0 ) {
        for( len = 0, i = 0; i < 4 && feof( infile ) == 0; i++ ) {
            v = 0;
            while( feof( infile ) == 0 && v == 0 ) {
                v = getc( infile );
                if( feof( infile ) == 0 ) {
                    v = ((v < 43 || v > 122) ? 0 : (int) cd64[ v - 43 ]);
                    if( v != 0 ) {
                        v = ((v == (int)'$') ? 0 : v - 61);
                    }
                }
            }
            if( feof( infile ) == 0 ) {
                len++;
                if( v != 0 ) {
                    in[ i ] = (unsigned char) (v - 1);
                }
            }
            else {
                in[i] = (unsigned char) 0;
            }
        }
        if( len > 0 ) {
            decodeblock( in, out );
            for( i = 0; i < len - 1; i++ ) {
                if( putc( (int) out[i], outfile ) == EOF ){
                    if( ferror( outfile ) != 0 )      {
                        perror( b64_message( B64_FILE_IO_ERROR ) );
                        retcode = B64_FILE_IO_ERROR;
                    }
                    break;
                }
            }
        }
    }
    return( retcode );
}

#include <SdFat.h>
#include <SdFatUtil.h>
#include <stdio.h>
#include <stdlib.h>
#include <SPI.h>
SdFat SD;

File myFile;

#define B64_DEF_LINE_SIZE   72
#define B64_MIN_LINE_SIZE    4

#define THIS_OPT(ac, av) ((char)(ac > 1 ? av[1][0] == '-' ? av[1][1] : 0 : 0))

char name[] = "a.jpg";
const boolean debugPrint = true;    // print details of process over serial?

SdFat sd;
SdFile file;
const uint8_t chipSelect = 8;          // pin that the SD is connected to (d8 for SparkFun MicroSD shield)


/*
** Translation Table as described in RFC1113
*/
static const char cb64[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/*
** Translation Table to decode (created by author)
*/
static const char cd64[]="|$$$}rstuvwxyz{$$$$$$$>?@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[\]^_`abcdefghijklmnopq";

/*
** returnable errors
**
** Error codes returned to the operating system.
**
*/
#define B64_SYNTAX_ERROR        1
#define B64_FILE_ERROR          2
#define B64_FILE_IO_ERROR       3
#define B64_ERROR_OUT_CLOSE     4
#define B64_LINE_SIZE_TO_MIN    5
#define B64_SYNTAX_TOOMANYARGS  6

/*
** b64_message
**
** Gather text messages in one place.
**
*/
#define B64_MAX_MESSAGES 7
static char *b64_msgs[ B64_MAX_MESSAGES ] = {
            "b64:000:Invalid Message Code.",
            "b64:001:Syntax Error -- check help (-h) for usage.",
            "b64:002:File Error Opening/Creating Files.",
            "b64:003:File I/O Error -- Note: output file not removed.",
            "b64:004:Error on output file close.",
            "b64:005:linesize set to minimum.",
            "b64:006:Syntax: Too many arguments."
};

#define b64_message( ec ) ((ec > 0 && ec < B64_MAX_MESSAGES ) ? b64_msgs[ ec ] : b64_msgs[ 0 ])

/*
** encodeblock
**
** encode 3 8-bit binary bytes as 4 '6-bit' characters
*/
static void encodeblock( unsigned char *in, unsigned char *out, int len )
{
    out[0] = (unsigned char) cb64[ (int)(in[0] >> 2) ];
    out[1] = (unsigned char) cb64[ (int)(((in[0] & 0x03) << 4) | ((in[1] & 0xf0) >> 4)) ];
    out[2] = (unsigned char) (len > 1 ? cb64[ (int)(((in[1] & 0x0f) << 2) | ((in[2] & 0xc0) >> 6)) ] : '=');
    out[3] = (unsigned char) (len > 2 ? cb64[ (int)(in[2] & 0x3f) ] : '=');
}


/*
** decodeblock
**
** decode 4 '6-bit' characters into 3 8-bit binary bytes
*/
static void decodeblock( unsigned char *in, unsigned char *out )
{
    out[ 0 ] = (unsigned char ) (in[0] << 2 | in[1] >> 4);
    out[ 1 ] = (unsigned char ) (in[1] << 4 | in[2] >> 2);
    out[ 2 ] = (unsigned char ) (((in[2] << 6) & 0xc0) | in[3]);
}

/*
** decode
**
** decode a base64 encoded stream discarding padding, line breaks and noise
*/
static int decode()
{
  int retcode = 0;
  unsigned char in[4];
  unsigned char out[3];
  int v;
  int i, len;

  *in = (unsigned char) 0;
  *out = (unsigned char) 0;
  while( myFile.available() ) {
        for( len = 0, i = 0; i < 4 && myFile.available(); i++ ) {
            v = 0;
            while( myFile.available() && v == 0 ) {
                v =myFile.read();
                if( myFile.available() ) {
                 v = ((v < 43 || v > 122) ? 0 : (int) cd64[ v - 43 ]);
          if( v != 0 ) {
            v = ((v == (int)'$') ? 0 : v - 61);
          }
                }
            }
            if(myFile.available() ) {
                len++;
                if( v != 0 ) {
                    in[ i ] = (unsigned char) (v - 1);
                }
            }
            else {
                in[i] = (unsigned char) 0;
            }
        }
        if( len > 0 ) {
            decodeblock( in, out );
            for( i = 0; i < len - 1; i++ ) {
                if( file.write((int)out[i])){
                  break;
        }
            }
        }
  }
}

void setup()
{
  myFile = SD.open("a.b64");
  // SD setup
  Serial.begin(9600);
  if (!sd.begin(SS, SD_SCK_MHZ(50))) {
    sd.initErrorHalt();
  }
  file.open(name, O_CREAT | O_EXCL | O_WRITE);
  decode();
  file.close();
}
void loop()
{

}