1 files changed, 93 insertions, 0 deletions
diff --git a/src/mscorlib/shared/System/StringSpanHelpers.cs b/src/mscorlib/shared/System/StringSpanHelpers.cs
new file mode 100644
index 0000000000..bdfd965641
--- /dev/null
+++ b/src/mscorlib/shared/System/StringSpanHelpers.cs
@@ -0,0 +1,93 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Globalization;
+
+namespace System
+{
+    /// <summary>Helpers for string-like operations on spans of chars.</summary>
+    internal static class StringSpanHelpers
+    {
+        // TODO https://github.com/dotnet/corefx/issues/21395: Provide public, efficient implementations
+
+        public static bool Equals(this ReadOnlySpan<char> left, ReadOnlySpan<char> right, StringComparison comparisonType) =>
+            comparisonType == StringComparison.Ordinal ? Equals(left, right) :
+            comparisonType == StringComparison.OrdinalIgnoreCase ? EqualsOrdinalIgnoreCase(left, right) :
+            throw new ArgumentOutOfRangeException(nameof(comparisonType));
+
+        public static bool Equals(this ReadOnlySpan<char> left, string right) =>
+            Equals(left, right.AsReadOnlySpan());
+
+        public static bool Equals(this ReadOnlySpan<char> left, ReadOnlySpan<char> right)
+        {
+            if (left.Length != right.Length)
+            {
+                return false;
+            }
+
+            for (int i = 0; i < left.Length; i++)
+            {
+                if (left[i] != right[i])
+                {
+                    return false;
+                }
+            }
+            
+            return true;
+        }
+
+        private static bool EqualsOrdinalIgnoreCase(this ReadOnlySpan<char> left, ReadOnlySpan<char> right)
+        {
+            if (left.Length != right.Length)
+            {
+                return false;
+            }
+
+            for (int i = 0; i < left.Length; i++)
+            {
+                char x = left[i], y = right[i];
+                if (x != y &&
+                    TextInfo.ToUpperAsciiInvariant(x) != TextInfo.ToUpperAsciiInvariant(y))
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        public static ReadOnlySpan<char> Trim(this ReadOnlySpan<char> source)
+        {
+            int startIndex = 0, endIndex = source.Length - 1;
+
+            while (startIndex <= endIndex && char.IsWhiteSpace(source[startIndex]))
+            {
+                startIndex++;
+            }
+
+            while (endIndex >= startIndex && char.IsWhiteSpace(source[endIndex]))
+            {
+                endIndex--;
+            }
+
+            return source.Slice(startIndex, endIndex - startIndex + 1);
+        }
+
+        public static int IndexOf(this ReadOnlySpan<char> source, char value) =>
+            IndexOf(source, value, 0);
+
+        public static int IndexOf(this ReadOnlySpan<char> source, char value, int startIndex)
+        {
+            for (int i = startIndex; i < source.Length; i++)
+            {
+                if (source[i] == value)
+                {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+    }
+}