https://opensource.apple.com/source/QuickTimeStreamingServer/QuickTimeStreamingServer-452/CommonUtilitiesLib/base64.c

BASE64 DECODE - APPLE.c

	static const unsigned char pr2six[ 256 ] =
	{
		/* ASCII table */
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
		52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
		64,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
		15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
		64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
		41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
		64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
	};

	int base64_decode( char* bufplain , const char* bufcoded ) {
		int nbytesdecoded;
		register const unsigned char* bufin;
		register unsigned char* bufout;
		register int nprbytes;

		bufin = ( const unsigned char* )bufcoded;
		while ( pr2six[ *( bufin++ ) ] <= 63 );
		nprbytes = ( bufin - ( const unsigned char* )bufcoded ) - 1;
		nbytesdecoded = ( ( nprbytes + 3 ) / 4 ) * 3;

		bufout = ( unsigned char* )bufplain;
		bufin = ( const unsigned char* )bufcoded;

		while ( nprbytes > 4 ) {
			*( bufout++ ) =
				( unsigned char )( pr2six[ *bufin ] << 2 | pr2six[ bufin[ 1 ] ] >> 4 );
			*( bufout++ ) =
				( unsigned char )( pr2six[ bufin[ 1 ] ] << 4 | pr2six[ bufin[ 2 ] ] >> 2 );
			*( bufout++ ) =
				( unsigned char )( pr2six[ bufin[ 2 ] ] << 6 | pr2six[ bufin[ 3 ] ] );
			bufin += 4;
			nprbytes -= 4;
		}

		/* Note: (nprbytes == 1) would be an error, so just ingore that case */
		if ( nprbytes > 1 ) {
			*( bufout++ ) =
				( unsigned char )( pr2six[ *bufin ] << 2 | pr2six[ bufin[ 1 ] ] >> 4 );
		}
		if ( nprbytes > 2 ) {
			*( bufout++ ) =
				( unsigned char )( pr2six[ bufin[ 1 ] ] << 4 | pr2six[ bufin[ 2 ] ] >> 2 );
		}
		if ( nprbytes > 3 ) {
			*( bufout++ ) =
				( unsigned char )( pr2six[ bufin[ 2 ] ] << 6 | pr2six[ bufin[ 3 ] ] );
		}

		*( bufout++ ) = '\0';
		nbytesdecoded -= ( 4 - nprbytes ) & 3;
		return nbytesdecoded;
	}