Optimized rune methods for length edge cases and ascii-only strings

Author: pl752

src/FirebirdSql.Data.FirebirdClient/Common/Extensions.cs

@@ -105,11 +105,18 @@ public static Encoding GetANSIEncoding()
 
 	public static int CountRunes(this ReadOnlySpan<char> text)
 	{
-		var count = 0;
-		var i = 0;
-		while(i < text.Length)
+		var length = text.Length;
+		if(length == 0)
+			return 0;
+
+		var i = text.IndexOfAnyInRange('\uD800', '\uDBFF');
+		if(i < 0)
+			return length;
+
+		var count = i;
+		while(i < length)
 		{
-			if(char.IsHighSurrogate(text[i]) && i + 1 < text.Length && char.IsLowSurrogate(text[i + 1]))
+			if(char.IsHighSurrogate(text[i]) && i + 1 < length && char.IsLowSurrogate(text[i + 1]))
 			{
 				i += 2;
 			}
@@ -124,24 +131,30 @@ public static int CountRunes(this ReadOnlySpan<char> text)
 
 	public static ReadOnlySpan<char> TruncateStringToRuneCount(this ReadOnlySpan<char> text, int maxRuneCount)
 	{
-		var count = 0;
-		var i = 0;
-		while(i < text.Length && count < maxRuneCount)
+		if(maxRuneCount <= 0 || text.IsEmpty)
+			return ReadOnlySpan<char>.Empty;
+
+		var length = text.Length;
+		if(maxRuneCount >= length)
+			return text;
+
+		var prefix = text[..maxRuneCount];
+		var i = prefix.IndexOfAnyInRange('\uD800', '\uDBFF');
+		if(i < 0)
+			return prefix;
+
+		var remaining = maxRuneCount - i;
+		while(i < length && remaining > 0)
 		{
-			var nextI = i;
-			if(char.IsHighSurrogate(text[i]) && i + 1 < text.Length && char.IsLowSurrogate(text[i + 1]))
+			if(char.IsHighSurrogate(text[i]) && i + 1 < length && char.IsLowSurrogate(text[i + 1]))
 			{
-				nextI += 2;
+				i += 2;
 			}
 			else
 			{
-				nextI++;
-			}
-			count++;
-			if(count <= maxRuneCount)
-			{
-				i = nextI;
+				i++;
 			}
+			remaining--;
 		}
 		return text[..i];
 	}