Fix handling of '\0' in Ascii.Trim (#105350)

dotnet · Jul 23, 2024 · f68d8e1 · f68d8e1
1 parent 1a79a65
commit f68d8e1
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Showing 2 changed files with 19 additions and 5 deletions.
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Trimming.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Trimming.cs
@@ -40,8 +40,11 @@ public static partial class Ascii
         private static Range TrimHelper<T>(ReadOnlySpan<T> value, TrimType trimType)
             where T : unmanaged, IBinaryInteger<T>
         {
+            // A bitmap with a bit set for each ASCII whitespace character. The set bit is at the
+            // index of the character minus 1, since we're using a 32-bit value and space would otherwise
+            // be at index 32; with -1, it's at index 31.
             const uint TrimMask =
-                (1u << (0x09 - 1))
+                  (1u << (0x09 - 1))
                 | (1u << (0x0A - 1))
                 | (1u << (0x0B - 1))
                 | (1u << (0x0C - 1))
@@ -53,8 +56,8 @@ private static Range TrimHelper<T>(ReadOnlySpan<T> value, TrimType trimType)
             {
                 for (; start < value.Length; start++)
                 {
-                    uint elementValue = uint.CreateTruncating(value[start]);
-                    if ((elementValue > 0x20) || ((TrimMask & (1u << ((int)elementValue - 1))) == 0))
+                    uint elementValueM1 = uint.CreateTruncating(value[start]) - 1;
+                    if ((elementValueM1 > 0x1F) || ((TrimMask & (1u << ((int)elementValueM1))) == 0))
                     {
                         break;
                     }
@@ -66,8 +69,8 @@ private static Range TrimHelper<T>(ReadOnlySpan<T> value, TrimType trimType)
             {
                 for (; start <= end; end--)
                 {
-                    uint elementValue = uint.CreateTruncating(value[end]);
-                    if ((elementValue > 0x20) || ((TrimMask & (1u << ((int)elementValue - 1))) == 0))
+                    uint elementValueM1 = uint.CreateTruncating(value[end]) - 1;
+                    if ((elementValueM1 > 0x1F) || ((TrimMask & (1u << ((int)elementValueM1))) == 0))
                     {
                         break;
                     }

diff --git a/src/libraries/System.Runtime/tests/System.Text.Encoding.Tests/Ascii/TrimTests.cs b/src/libraries/System.Runtime/tests/System.Text.Encoding.Tests/Ascii/TrimTests.cs
@@ -22,6 +22,7 @@ public static void EmptyInput()
         [InlineData("1")]
         [InlineData("abc")]
         [InlineData("a\tb c\rd\ne")]
+        [InlineData("\0abcde\0")]
         public static void NothingToTrimNonEmptyInput(string text)
         {
             ReadOnlySpan<byte> bytes = Encoding.ASCII.GetBytes(text);
@@ -113,5 +114,15 @@ public static void StartingAndEndingWithWhitespace(string text, int leadingWhite
             Assert.Equal(0..(text.Length - trailingWhitespaceCount), Ascii.TrimEnd(bytes));
             Assert.Equal(0..(text.Length - trailingWhitespaceCount), Ascii.TrimEnd(text));
         }
+
+        [Fact]
+        public static void OnlyAsciiWhitespaceCharactersAreTrimmed()
+        {
+            for (int i = 0; i <= char.MaxValue; i++)
+            {
+                bool trimmed = Ascii.Trim(((char)i).ToString()).Equals(1..1);
+                Assert.True(((char)i is '\t' or '\n' or '\v' or '\f' or '\r' or ' ') == trimmed, $"Failed at {i}");
+            }
+        }
     }
 }