Replace some single-char strings with chars (#81831)

* Replace some single-char strings with chars

Also a few other minor improvements noticed along the way.

* Update src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessManager.Windows.cs

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/ThunkedApis.cs

@@ -210,7 +210,7 @@ private static void SplitTypeName(string fullname, out string name, out string n
             Debug.Assert(fullname != null);
 
             // Get namespace
-            int nsDelimiter = fullname.LastIndexOf(".", StringComparison.Ordinal);
+            int nsDelimiter = fullname.LastIndexOf('.');
             if (nsDelimiter != -1)
             {
                 ns = fullname.Substring(0, nsDelimiter);

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/MethodInfos/RuntimeMethodHelpers.cs

@@ -78,7 +78,7 @@ internal static string ComputeParametersString(RuntimeParameterInfo[] parameters
                 // Legacy: Why use "ByRef" for by ref parameters? What language is this?
                 // VB uses "ByRef" but it should precede (not follow) the parameter name.
                 // Why don't we just use "&"?
-                if (parameterTypeString.EndsWith("&"))
+                if (parameterTypeString.EndsWith('&'))
                 {
                     sb.Append(parameterTypeString, 0, parameterTypeString.Length - 1);
                     sb.Append(" ByRef");

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.GetMember.cs

@@ -29,7 +29,7 @@ public sealed override MemberInfo[] GetMember(string name, MemberTypes type, Bin
 
         private MemberInfo[] GetMemberImpl(string optionalNameOrPrefix, MemberTypes type, BindingFlags bindingAttr)
         {
-            bool prefixSearch = optionalNameOrPrefix != null && optionalNameOrPrefix.EndsWith("*", StringComparison.Ordinal);
+            bool prefixSearch = optionalNameOrPrefix != null && optionalNameOrPrefix.EndsWith('*');
             string? optionalName = prefixSearch ? null : optionalNameOrPrefix;
 
             Func<MemberInfo, bool>? predicate = null;

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/LocalAppContextSwitches.cs

@@ -18,21 +18,11 @@ private static bool InitializeDefaultActivityIdFormat()
                 string? switchValue = Environment.GetEnvironmentVariable("DOTNET_SYSTEM_DIAGNOSTICS_DEFAULTACTIVITYIDFORMATISHIERARCHIAL");
                 if (switchValue != null)
                 {
-                    defaultActivityIdFormatIsHierarchial = IsTrueStringIgnoreCase(switchValue) || switchValue.Equals("1");
+                    defaultActivityIdFormatIsHierarchial = switchValue.Equals("true", StringComparison.OrdinalIgnoreCase) || switchValue.Equals("1");
                 }
             }
 
             return defaultActivityIdFormatIsHierarchial;
         }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static bool IsTrueStringIgnoreCase(string value)
-        {
-            return value.Length == 4 &&
-                    (value[0] == 't' || value[0] == 'T') &&
-                    (value[1] == 'r' || value[1] == 'R') &&
-                    (value[2] == 'u' || value[2] == 'U') &&
-                    (value[3] == 'e' || value[3] == 'E');
-        }
     }
 }

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessManager.Windows.cs

@@ -527,7 +527,7 @@ private static ProcessInfo[] GetProcessInfos(PerformanceCounterLib library, int
                                 // at the end.  If instanceName ends in ".", ".e", or ".ex" we remove it.
                                 if (instanceName.Length == 15)
                                 {
-                                    if (instanceName.EndsWith(".", StringComparison.Ordinal))
+                                    if (instanceName.EndsWith("."))
                                     {
                                         instanceName = instanceName.Slice(0, 14);
                                     }

src/libraries/System.Drawing.Common/src/System/Drawing/FontConverter.cs

@@ -38,7 +38,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, [NotNullWhen(
                     ValueStringBuilder sb = default;
                     sb.Append(font.Name);
                     sb.Append(culture.TextInfo.ListSeparator[0]);
-                    sb.Append(" ");
+                    sb.Append(' ');
                     sb.Append(font.Size.ToString(culture.NumberFormat));
 
                     switch (font.Unit)

src/libraries/System.Net.HttpListener/src/System/Net/ServiceNameStore.cs

@@ -270,8 +270,8 @@ public static string[] BuildServiceNames(string uriPrefix)
         {
             string hostname = ExtractHostname(uriPrefix, true)!;
 
-            if (string.Equals(hostname, "*", StringComparison.OrdinalIgnoreCase) ||
-                string.Equals(hostname, "+", StringComparison.OrdinalIgnoreCase) ||
+            if (hostname == "*" ||
+                hostname == "+" ||
                 IPAddress.TryParse(hostname, out _))
             {
                 // for a wildcard, register the machine name.  If the caller doesn't have DNS permission

src/libraries/System.Net.HttpListener/src/System/Net/Windows/HttpListener.Windows.cs

@@ -1579,8 +1579,8 @@ private static void SendError(HttpListenerSession session, ulong requestId, Http
                 httpResponse.pReason = (sbyte*)pReason;
                 httpResponse.ReasonLength = (ushort)byteReason.Length;
 
-                byte[] byteContentLength = Encoding.Default.GetBytes("0");
-                fixed (byte* pContentLength = &byteContentLength[0])
+                ReadOnlySpan<byte> byteContentLength = "0"u8;
+                fixed (byte* pContentLength = byteContentLength)
                 {
                     (&httpResponse.Headers.KnownHeaders)[(int)HttpResponseHeader.ContentLength].pRawValue = (sbyte*)pContentLength;
                     (&httpResponse.Headers.KnownHeaders)[(int)HttpResponseHeader.ContentLength].RawValueLength = (ushort)byteContentLength.Length;

src/libraries/System.Private.CoreLib/src/System/AppContextConfigHelper.cs

@@ -88,7 +88,7 @@ internal static short GetInt16Config(string configName, short defaultValue, bool
                         {
                             result = Convert.ToInt16(str, 16);
                         }
-                        else if (str.StartsWith("0"))
+                        else if (str.StartsWith('0'))
                         {
                             result = Convert.ToInt16(str, 8);
                         }

src/libraries/System.Private.CoreLib/src/System/Runtime/Loader/LibraryNameVariation.Windows.cs

@@ -16,7 +16,7 @@ internal static IEnumerable<LibraryNameVariation> DetermineLibraryNameVariations
             yield return new LibraryNameVariation(string.Empty, string.Empty);
 
             if (isRelativePath
-                && !libName.EndsWith(".", StringComparison.OrdinalIgnoreCase)
+                && !libName.EndsWith('.')
                 && !libName.EndsWith(".dll", StringComparison.OrdinalIgnoreCase)
                 && !libName.EndsWith(".exe", StringComparison.OrdinalIgnoreCase))
             {

src/libraries/System.Speech/src/Internal/SrgsParser/XmlParser.cs

@@ -361,7 +361,7 @@ private void ParseGrammar(XmlReader reader, IGrammar grammar)
                                 catch (ArgumentException)
                                 {
                                     // Unknown Culture info, fall back to the base culture.
-                                    int pos = reader.Value.IndexOf("-", StringComparison.Ordinal);
+                                    int pos = reader.Value.IndexOf('-');
                                     if (pos > 0)
                                     {
                                         grammar.Culture = _langId = new CultureInfo(reader.Value.Substring(0, pos));
@@ -1767,7 +1767,7 @@ private static void SetRepeatValues(string repeat, out int minRepeat, out int ma
             minRepeat = maxRepeat = 1;
             if (!string.IsNullOrEmpty(repeat))
             {
-                int sep = repeat.IndexOf("-", StringComparison.Ordinal);
+                int sep = repeat.IndexOf('-');
 
                 if (sep < 0)
                 {

src/libraries/System.Speech/src/Internal/Synthesis/SSmlParser.cs

@@ -128,7 +128,7 @@ private static void ProcessSpeakElement(XmlReader reader, ISsmlParser engine, ob
                             {
                                 innerException = e;
                                 // Unknown Culture info, fall back to the base culture.
-                                int pos = reader.Value.IndexOf("-", StringComparison.Ordinal);
+                                int pos = reader.Value.IndexOf('-');
                                 if (pos > 0)
                                 {
                                     try

src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs

@@ -162,7 +162,7 @@ private static void SplitName(string? fullname, out string? name, out string? ns
                 return;
 
             // Get namespace
-            int nsDelimiter = fullname.LastIndexOf(".", StringComparison.Ordinal);
+            int nsDelimiter = fullname.LastIndexOf('.');
             if (nsDelimiter != -1)
             {
                 ns = fullname.Substring(0, nsDelimiter);
@@ -236,7 +236,7 @@ private static void FilterHelper(
                     listType = MemberListType.CaseSensitive;
                 }
 
-                if (allowPrefixLookup && name.EndsWith("*", StringComparison.Ordinal))
+                if (allowPrefixLookup && name.EndsWith('*'))
                 {
                     // We set prefixLookup to true if name ends with a "*".
                     // We will also set listType to All so that all members are included in