base64.ino

/************************************************************************************
* base64 related stuff
************************************************************************************/
static char encoding_table[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
    'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
    'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
    'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
    'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
    'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
    'w', 'x', 'y', 'z', '0', '1', '2', '3',
    '4', '5', '6', '7', '8', '9', '+', '/'
};


static int mod_table[] = { 0, 2, 1 };


char * base64_encode( const char *data, size_t input_length, size_t * output_length, char *encoded_data )
{

    int i, j;

    *output_length = 4 * ( ( input_length + 2 ) / 3 );

    for ( i = 0, j = 0; i < input_length; )
    {
        uint32_t octet_a = i < input_length ? ( unsigned char ) data[i++] : 0;
        uint32_t octet_b = i < input_length ? ( unsigned char ) data[i++] : 0;
        uint32_t octet_c = i < input_length ? ( unsigned char ) data[i++] : 0;

        uint32_t triple = ( octet_a << 0x10 ) + ( octet_b << 0x08 ) + octet_c;

        encoded_data[j++] = encoding_table[( triple >> 3 * 6 ) & 0x3F];
        encoded_data[j++] = encoding_table[( triple >> 2 * 6 ) & 0x3F];
        encoded_data[j++] = encoding_table[( triple >> 1 * 6 ) & 0x3F];
        encoded_data[j++] = encoding_table[( triple >> 0 * 6 ) & 0x3F];
    }

    for ( i = 0; i < mod_table[input_length % 3]; i++ )
        encoded_data[*output_length - 1 - i] = '=';

    return encoded_data;
}