Merge PR icsharpcode#301: Revert ArraySegment simplification to speed up CRC32 calculation

Author: decipherer

src/ICSharpCode.SharpZipLib/Checksum/BZip2Crc.cs

@@ -177,10 +177,11 @@ public void Update(byte[] buffer)
 		/// </param>
 		public void Update(ArraySegment<byte> segment)
 		{
-			foreach (byte b in segment)
-			{
-				Update(b);
-			}
+			var count = segment.Count;
+			var offset = segment.Offset;
+
+			while (--count >= 0)
+				Update(segment.Array[offset++]);
 		}
 	}
 }

src/ICSharpCode.SharpZipLib/Checksum/Crc32.cs

@@ -166,10 +166,11 @@ public void Update(byte[] buffer)
 		/// </param>
 		public void Update(ArraySegment<byte> segment)
 		{
-			foreach (byte b in segment)
-			{
-				Update(b);
-			}
+			var count = segment.Count;
+			var offset = segment.Offset;
+
+			while (--count >= 0)
+				Update(segment.Array[offset++]);
 		}
 	}
 }