New API, and bug fix

Author: migueldeicaza

NStack/unicode/Rune.ColumnWidth.cs

@@ -94,7 +94,7 @@ public static int ColumnWidth (Rune rune)
 			if (irune >= 0x7f && irune <= 0xa0)
 				return 0;
 			/* binary search in table of non-spacing characters */
-			if (bisearch (irune, combining, combining.GetLength (0)) != 0)
+			if (bisearch (irune, combining, combining.GetLength (0)-1) != 0)
 				return 0;
 			/* if we arrive here, ucs is not a combining or C0/C1 control character */
 			return 1 +

NStack/unicode/Rune.extensions.cs

@@ -272,6 +272,21 @@ public static bool Valid (ustring str)
 			return InvalidIndex (str) == -1;
 		}
 
-
+		/// <summary>
+		/// Given one byte from a utf8 string, return the number of expected bytes that make up the sequence.
+		/// </summary>
+		/// <returns>The number of UTF8 bytes expected given the first prefix.</returns>
+		/// <param name="firstByte">Is the first byte of a UTF8 sequence.</param>
+		public static int ExpectedSizeFromFirstByte (byte firstByte)
+		{
+			var x = first [firstByte];
+
+			// Invalid runes, just return 1 for byte, and let higher level pass to print
+			if (x == xx)
+				return -1;
+			if (x == a1)
+				return 1;
+			return x & 0xf;
+		}
 	}
 }