base64 인코딩 / 디코딩

/*------ Base64 Encoding Table ------*/
static const char MimeBase64[] = {
	'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', '+', '/'
};
/*------ Base64 Decoding Table ------*/
static int DecodeMimeBase64[256] = {
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 00-0F */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 10-1F */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,  /* 20-2F */
	52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,  /* 30-3F */
	-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,  /* 40-4F */
	15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,  /* 50-5F */
	-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,  /* 60-6F */
	41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,  /* 70-7F */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 80-8F */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* 90-9F */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* A0-AF */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* B0-BF */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* C0-CF */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* D0-DF */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  /* E0-EF */
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1   /* F0-FF */
};

int base64_decode( char *text, unsigned char *dst, int numBytes )
{
	const char* cp;
	int space_idx = 0, phase;
	int d, prev_d = 0;
	unsigned char c;
	space_idx = 0;
	phase = 0;
	for( cp = text; *cp != '\0'; ++cp ) {
		d = DecodeMimeBase64[(int)*cp];
		if( d != -1 ) {
			switch( phase ) {
			case 0:
				++phase;
				break;
			case 1:
				c = ((prev_d << 2) | ((d & 0x30) >> 4));
				if( space_idx < numBytes )
					dst[space_idx++] = c;
				++phase;
				break;
			case 2:
				c = (((prev_d & 0xf) << 4) | ((d & 0x3c) >> 2));
				if( space_idx < numBytes )
					dst[space_idx++] = c;
				++phase;
				break;
			case 3:
				c = (((prev_d & 0x03) << 6) | d);
				if( space_idx < numBytes )
					dst[space_idx++] = c;
				phase = 0;
				break;
			}
			prev_d = d;
		}
	}
	return space_idx;
}

int base64_encode( char *text, int numBytes, char **encodedText )
{
	unsigned char input[3] = { 0, 0, 0 };
	unsigned char output[4] = { 0, 0, 0, 0 };
	int   index, i, j, size;
	char *p, *plen;
	plen = text + numBytes - 1;
	size = (4 * (numBytes / 3)) + (numBytes % 3 ? 4 : 0) + 1;
	(*encodedText) = (char*)malloc( size );
	j = 0;
	for( i = 0, p = text; p <= plen; i++, p++ ) {
		index = i % 3;
		input[index] = *p;
		if( index == 2 || p == plen ) {
			output[0] = ((input[0] & 0xFC) >> 2);
			output[1] = ((input[0] & 0x3) << 4) | ((input[1] & 0xF0) >> 4);
			output[2] = ((input[1] & 0xF) << 2) | ((input[2] & 0xC0) >> 6);
			output[3] = (input[2] & 0x3F);
			(*encodedText)[j++] = MimeBase64[output[0]];
			(*encodedText)[j++] = MimeBase64[output[1]];
			(*encodedText)[j++] = index == 0 ? '=' : MimeBase64[output[2]];
			(*encodedText)[j++] = index <  2 ? '=' : MimeBase64[output[3]];
			input[0] = input[1] = input[2] = 0;
		}
	}
	(*encodedText)[j] = '\0';
	return size;
}