System.Xml.XmlReaderBinarySupport.ReadBase64 C# (CSharp) Méthode

		public int ReadBase64 (byte [] buffer, int offset, int length)
		{
			if (offset < 0)
				throw CreateArgumentOutOfRangeException ("offset", offset, "Offset must be non-negative integer.");
			else if (length < 0)
				throw CreateArgumentOutOfRangeException ("length", length, "Length must be non-negative integer.");
			else if (buffer.Length < offset + length)
				throw new ArgumentOutOfRangeException ("buffer length is smaller than the sum of offset and length.");

			if (reader.IsEmptyElement)
				return 0;
			if (length == 0)	// It does not raise an error.
				return 0;

			int bufIndex = offset;
			int bufLast = offset + length;

			if (base64CacheStartsAt >= 0) {
				for (int i = base64CacheStartsAt; i < 3; i++) {
					buffer [bufIndex++] = base64Cache [base64CacheStartsAt++];
					if (bufIndex == bufLast)
						return bufLast - offset;
				}
			}

			for (int i = 0; i < 3; i++)
				base64Cache [i] = 0;
			base64CacheStartsAt = -1;

			int max = (int) System.Math.Ceiling (4.0 / 3 * length);
			int additional = max % 4;
			if (additional > 0)
				max += 4 - additional;
			char [] chars = new char [max];
			int charsLength = getter != null ?
				getter (chars, 0, max) :
				ReadValueChunk (chars, 0, max);

			byte b = 0;
			byte work = 0;
			for (int i = 0; i < charsLength - 3; i++) {
				if ((i = SkipIgnorableBase64Chars (chars, charsLength, i)) == charsLength)
					break;
				b = (byte) (GetBase64Byte (chars [i]) << 2);
				if (bufIndex < bufLast)
					buffer [bufIndex] = b;
				else {
					if (base64CacheStartsAt < 0)
						base64CacheStartsAt = 0;
					base64Cache [0] = b;
				}
				// charsLength mod 4 might not equals to 0.
				if (++i == charsLength)
					break;
				if ((i = SkipIgnorableBase64Chars (chars, charsLength, i))  == charsLength)
					break;
				b = GetBase64Byte (chars [i]);
				work = (byte) (b >> 4);
				if (bufIndex < bufLast) {
					buffer [bufIndex] += work;
					bufIndex++;
				}
				else
					base64Cache [0] += work;

				work = (byte) ((b & 0xf) << 4);
				if (bufIndex < bufLast) {
					buffer [bufIndex] = work;
				}
				else {
					if (base64CacheStartsAt < 0)
						base64CacheStartsAt = 1;
					base64Cache [1] = work;
				}

				if (++i == charsLength)
					break;
				if ((i = SkipIgnorableBase64Chars (chars, charsLength, i)) == charsLength)
					break;
				b = GetBase64Byte (chars [i]);
				work = (byte) (b >> 2);
				if (bufIndex < bufLast) {
					buffer [bufIndex] += work;
					bufIndex++;
				}
				else
					base64Cache [1] += work;

				work = (byte) ((b & 3) << 6);
				if (bufIndex < bufLast)
					buffer [bufIndex] = work;
				else {
					if (base64CacheStartsAt < 0)
						base64CacheStartsAt = 2;
					base64Cache [2] = work;
				}
				if (++i == charsLength)
					break;
				if ((i = SkipIgnorableBase64Chars (chars, charsLength, i)) == charsLength)
					break;
				work = GetBase64Byte (chars [i]);
				if (bufIndex < bufLast) {
					buffer [bufIndex] += work;
					bufIndex++;
				}
				else
					base64Cache [2] += work;
			}
			int ret = System.Math.Min (bufLast - offset, bufIndex - offset);
			if (ret < length && charsLength > 0)
				return ret + ReadBase64 (buffer, offset + ret, length - ret);
			else
				return ret;
		}