Add methods to convert between hexadecimal strings and bytes

src/libraries/Common/src/System/HexConverter.cs

@@ -2,6 +2,7 @@
 // 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.Diagnostics;
 using System.Runtime.CompilerServices;
 
 namespace System
@@ -83,6 +84,16 @@ public static void ToCharsBuffer(byte value, Span<char> buffer, int startingInde
             buffer[startingIndex] = (char)(packedResult >> 8);
         }
 
+        public static void EncodeToUtf16(ReadOnlySpan<byte> bytes, Span<char> chars, Casing casing = Casing.Upper)
+        {
+            Debug.Assert(chars.Length >= bytes.Length * 2);
+
+            for (int pos = 0; pos < bytes.Length; ++pos)
+            {
+                ToCharsBuffer(bytes[pos], chars, pos * 2, casing);
+            }
+        }
+
 #if ALLOW_PARTIALLY_TRUSTED_CALLERS
         [System.Security.SecuritySafeCriticalAttribute]
 #endif
@@ -113,10 +124,7 @@ public static unsafe string ToString(ReadOnlySpan<byte> bytes, Casing casing = C
                 return string.Create(bytes.Length * 2, (Ptr: (IntPtr)bytesPtr, bytes.Length, casing), (chars, args) =>
                 {
                     var ros = new ReadOnlySpan<byte>((byte*)args.Ptr, args.Length);
-                    for (int pos = 0; pos < ros.Length; ++pos)
-                    {
-                        ToCharsBuffer(ros[pos], chars, pos * 2, args.casing);
-                    }
+                    EncodeToUtf16(ros, chars, args.casing);
                 });
             }
 #endif
@@ -149,5 +157,95 @@ public static char ToCharLower(int value)
 
             return (char)value;
         }
+
+        public static bool TryDecodeFromUtf16(ReadOnlySpan<char> chars, Span<byte> bytes)
+        {
+            return TryDecodeFromUtf16(chars, bytes, out _);
+        }
+
+        public static bool TryDecodeFromUtf16(ReadOnlySpan<char> chars, Span<byte> bytes, out int charsProcessed)
+        {
+            Debug.Assert(chars.Length % 2 == 0, "Un-even number of characters provided");
+            Debug.Assert(chars.Length / 2 == bytes.Length, "Target buffer not right-sized for provided characters");
+
+            int i = 0;
+            int j = 0;
+            int byteLo = 0;
+            int byteHi = 0;
+            while (j < bytes.Length)
+            {
+                byteLo = FromChar(chars[i + 1]);
+                byteHi = FromChar(chars[i]);
+
+                // byteHi hasn't been shifted to the high half yet, so the only way the bitwise or produces this pattern
+                // is if either byteHi or byteLo was not a hex character.
+                if ((byteLo | byteHi) == 0xFF)
+                    break;
+
+                bytes[j++] = (byte)((byteHi << 4) | byteLo);
+                i+=2;
+            }
+
+            if (byteLo == 0xFF)
+                i++;
+
+            charsProcessed = i;
+            return (byteLo | byteHi) != 0xFF;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int FromChar(int c)
+        {
+            ReadOnlySpan<byte> charToHexLookup = CharToHexLookup;
+            return c >= charToHexLookup.Length ? 0xFF : charToHexLookup[c];
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int FromUpperChar(int c)
+        {
+            ReadOnlySpan<byte> charToHexLookup = CharToHexLookup;
+            return c > 71 ? 0xFF : charToHexLookup[c];
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int FromLowerChar(int c)
+        {
+            if ('0' <= c && c <= '9')
+                return (byte)(c - '0');
+            if ('a' <= c && c <= 'f')
+                return (byte)(c - ('a' - 10));
+
+            return 0xFF;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsHexChar(int c)
+        {
+            return FromChar(c) != 0xFF;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsHexUpperChar(int c)
+        {
+            return (uint)(c - '0') <= 9 || (uint)(c - 'A') <= ('F' - 'A');
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsHexLowerChar(int c)
+        {
+            return (uint)(c - '0') <= 9 || (uint)(c - 'a') <= ('f' - 'a');
+        }
+
+        /// <summary>Map from an ASCII char to its hex value, e.g. arr['b'] == 11. 0xFF means it's not a hex digit.</summary>
+        private static ReadOnlySpan<byte> CharToHexLookup => new byte[]
+        {
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 15
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 31
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 47
+            0x0,  0x1,  0x2,  0x3,  0x4,  0x5,  0x6,  0x7,  0x8,  0x9,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 63
+            0xFF, 0xA,  0xB,  0xC,  0xD,  0xE,  0xF,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 79
+            0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 95
+            0xFF, 0xa,  0xb,  0xc,  0xd,  0xe,  0xf // 102
+        };
     }
 }

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

@@ -804,7 +804,7 @@ internal static bool TryConvertIdToContext(string id, out ActivityContext contex
             ReadOnlySpan<char> spanIdSpan  = id.AsSpan(36, 16);
 
             if (!ActivityTraceId.IsLowerCaseHexAndNotAllZeros(traceIdSpan) || !ActivityTraceId.IsLowerCaseHexAndNotAllZeros(spanIdSpan) ||
-                !ActivityTraceId.IsHexadecimalLowercaseChar(id[53]) || !ActivityTraceId.IsHexadecimalLowercaseChar(id[54]))
+                !HexConverter.IsHexLowerChar(id[53]) || !HexConverter.IsHexLowerChar(id[54]))
             {
                 return false;
             }
@@ -1136,7 +1136,7 @@ private void TrySetTraceFlagsFromParent()
                 }
                 else if (_parentId != null && IsW3CId(_parentId))
                 {
-                    if (ActivityTraceId.IsHexadecimalLowercaseChar(_parentId[53]) && ActivityTraceId.IsHexadecimalLowercaseChar(_parentId[54]))
+                    if (HexConverter.IsHexLowerChar(_parentId[53]) && HexConverter.IsHexLowerChar(_parentId[54]))
                     {
                         _w3CIdFlags = (byte)(ActivityTraceId.HexByteFromChars(_parentId[53], _parentId[54]) | ActivityTraceFlagsIsSet);
                     }
@@ -1408,15 +1408,14 @@ internal static void SetSpanFromHexChars(ReadOnlySpan<char> charData, Span<byte>
         }
         internal static byte HexByteFromChars(char char1, char char2)
         {
-            return (byte)(HexDigitToBinary(char1) * 16 + HexDigitToBinary(char2));
-        }
-        private static byte HexDigitToBinary(char c)
-        {
-            if ('0' <= c && c <= '9')
-                return (byte)(c - '0');
-            if ('a' <= c && c <= 'f')
-                return (byte)(c - ('a' - 10));
-            throw new ArgumentOutOfRangeException("idData");
+            int hi = HexConverter.FromLowerChar(char1);
+            int lo = HexConverter.FromLowerChar(char2);
+            if ((hi | lo) == 0xFF)
+            {
+                throw new ArgumentOutOfRangeException("idData");
+            }
+
+            return (byte)((hi << 4) | lo);
         }
 
         internal static bool IsLowerCaseHexAndNotAllZeros(ReadOnlySpan<char> idData)
@@ -1427,7 +1426,7 @@ internal static bool IsLowerCaseHexAndNotAllZeros(ReadOnlySpan<char> idData)
             for (; i < idData.Length; i++)
             {
                 char c = idData[i];
-                if (!IsHexadecimalLowercaseChar(c))
+                if (!HexConverter.IsHexLowerChar(c))
                 {
                     return false;
                 }
@@ -1440,13 +1439,6 @@ internal static bool IsLowerCaseHexAndNotAllZeros(ReadOnlySpan<char> idData)
 
             return isNonZero;
         }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal static bool IsHexadecimalLowercaseChar(char c)
-        {
-            // Between 0 - 9 or lowercased between a - f
-            return (uint)(c - '0') <= 9 || (uint)(c - 'a') <= ('f' - 'a');
-        }
     }
 
     /// <summary>

src/libraries/System.Net.Http/src/System/Net/Http/Headers/AltSvcHeaderParser.cs

@@ -307,20 +307,15 @@ private static bool TryReadUnknownPercentEncodedAlpnProtocolName(ReadOnlySpan<ch
         /// </summary>
         private static bool TryReadAlpnHexDigit(char ch, out int nibble)
         {
-            if ((uint)(ch - '0') <= '9' - '0') // ch >= '0' && ch <= '9'
+            int result = HexConverter.FromUpperChar(ch);
+            if (result == 0xFF)
             {
-                nibble = ch - '0';
-                return true;
-            }
-
-            if ((uint)(ch - 'A') <= 'F' - 'A') // ch >= 'A' && ch <= 'F'
-            {
-                nibble = ch - 'A' + 10;
-                return true;
+                nibble = 0;
+                return false;
             }
 
-            nibble = 0;
-            return false;
+            nibble = result;
+            return true;
         }
 
         private static bool TryReadQuotedAltAuthority(string value, int startIndex, out string? host, out int port, out int readLength)

src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/AuthenticationHelper.Digest.cs

@@ -237,17 +237,7 @@ private static string ComputeHash(string data, string algorithm)
                 bool hashComputed = hash.TryComputeHash(Encoding.UTF8.GetBytes(data), result, out int bytesWritten);
                 Debug.Assert(hashComputed && bytesWritten == result.Length);
 
-                StringBuilder sb = StringBuilderCache.Acquire(result.Length * 2);
-
-                Span<char> byteX2 = stackalloc char[2];
-                for (int i = 0; i < result.Length; i++)
-                {
-                    bool formatted = result[i].TryFormat(byteX2, out int charsWritten, "x2");
-                    Debug.Assert(formatted && charsWritten == 2);
-                    sb.Append(byteX2);
-                }
-
-                return StringBuilderCache.GetStringAndRelease(sb);
+                return HexConverter.ToString(result, HexConverter.Casing.Lower);
             }
         }
 

src/libraries/System.Net.HttpListener/src/System.Net.HttpListener.csproj

@@ -83,6 +83,8 @@
     <Compile Include="$(CommonPath)System\Net\WebSockets\WebSocketValidate.cs"
              Link="Common\System\Net\WebSockets\WebSocketValidate.cs" />
     <Compile Include="System\Net\Windows\CookieExtensions.cs" />
+    <Compile Include="$(CommonPath)System\HexConverter.cs"
+             Link="Common\System\HexConverter.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' == 'true' and '$(ForceManagedImplementation)' != 'true'">
     <Compile Include="System\Net\Windows\HttpListener.Windows.cs" />

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

@@ -438,12 +438,12 @@ private static string UrlDecodeStringFromStringInternal(string s, Encoding e)
                     {
                         if (s[pos + 1] == 'u' && pos < count - 5)
                         {
-                            int h1 = HexToInt(s[pos + 2]);
-                            int h2 = HexToInt(s[pos + 3]);
-                            int h3 = HexToInt(s[pos + 4]);
-                            int h4 = HexToInt(s[pos + 5]);
+                            int h1 = HexConverter.FromChar(s[pos + 2]);
+                            int h2 = HexConverter.FromChar(s[pos + 3]);
+                            int h3 = HexConverter.FromChar(s[pos + 4]);
+                            int h4 = HexConverter.FromChar(s[pos + 5]);
 
-                            if (h1 >= 0 && h2 >= 0 && h3 >= 0 && h4 >= 0)
+                            if ((h1 | h2 | h3 | h4) != 0xFF)
                             {   // valid 4 hex chars
                                 ch = (char)((h1 << 12) | (h2 << 8) | (h3 << 4) | h4);
                                 pos += 5;
@@ -455,10 +455,10 @@ private static string UrlDecodeStringFromStringInternal(string s, Encoding e)
                         }
                         else
                         {
-                            int h1 = HexToInt(s[pos + 1]);
-                            int h2 = HexToInt(s[pos + 2]);
+                            int h1 = HexConverter.FromChar(s[pos + 1]);
+                            int h2 = HexConverter.FromChar(s[pos + 2]);
 
-                            if (h1 >= 0 && h2 >= 0)
+                            if ((h1 | h2) != 0xFF)
                             {     // valid 2 hex chars
                                 byte b = (byte)((h1 << 4) | h2);
                                 pos += 2;
@@ -479,14 +479,6 @@ private static string UrlDecodeStringFromStringInternal(string s, Encoding e)
                 return helper.GetString();
             }
 
-            private static int HexToInt(char h)
-            {
-                return (h >= '0' && h <= '9') ? h - '0' :
-                (h >= 'a' && h <= 'f') ? h - 'a' + 10 :
-                (h >= 'A' && h <= 'F') ? h - 'A' + 10 :
-                -1;
-            }
-
             private class UrlDecoder
             {
                 private readonly int _bufferSize;

src/libraries/System.Net.NetworkInformation/src/System/Net/NetworkInformation/PhysicalAddress.cs

@@ -3,7 +3,6 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Diagnostics.CodeAnalysis;
-using System.Text;
 
 namespace System.Net.NetworkInformation
 {
@@ -92,7 +91,7 @@ public override bool Equals(object? comparand)
 
         public override string ToString()
         {
-            return HexConverter.ToString(_address.AsSpan(), HexConverter.Casing.Upper);
+            return Convert.ToHexString(_address ?? Array.Empty<byte>());
         }
 
         public byte[] GetAddressBytes()
@@ -185,20 +184,8 @@ public static bool TryParse(ReadOnlySpan<char> address, [NotNullWhen(true)] out
             for (int i = 0; i < address.Length; i++)
             {
                 int character = address[i];
-
-                if (character >= '0' && character <= '9')
-                {
-                    character -= '0';
-                }
-                else if (character >= 'A' && character <= 'F')
-                {
-                    character -= ('A' - 10);
-                }
-                else if (character >= 'a' && character <= 'f')
-                {
-                    character -= ('a' - 10);
-                }
-                else
+                int tmp;
+                if ((tmp = HexConverter.FromChar(character)) == 0xFF)
                 {
                     if (delimiter == character && validCount == validSegmentLength)
                     {
@@ -209,6 +196,8 @@ public static bool TryParse(ReadOnlySpan<char> address, [NotNullWhen(true)] out
                     return false;
                 }
 
+                character = tmp;
+
                 // we had too many characters after the last delimiter
                 if (validCount >= validSegmentLength)
                 {

src/libraries/System.Net.NetworkInformation/src/System/Net/NetworkInformation/StringParsingHelpers.Connections.cs

@@ -326,22 +326,13 @@ private static IPAddress ParseIPv6HexString(string hexAddress, bool isNetworkOrd
 
         private static byte HexToByte(char val)
         {
-            if (val <= '9' && val >= '0')
-            {
-                return (byte)(val - '0');
-            }
-            else if (val >= 'a' && val <= 'f')
-            {
-                return (byte)((val - 'a') + 10);
-            }
-            else if (val >= 'A' && val <= 'F')
-            {
-                return (byte)((val - 'A') + 10);
-            }
-            else
+            byte result = (byte)HexConverter.FromChar(val);
+            if (result == 0xFF)
             {
                 throw ExceptionHelper.CreateForParseFailure();
             }
+
+            return result;
         }
     }
 }

src/libraries/System.Net.NetworkInformation/tests/FunctionalTests/System.Net.NetworkInformation.Functional.Tests.csproj

@@ -51,6 +51,8 @@
              Link="Common\System\IO\StringParser.cs" />
     <Compile Include="$(CommonPath)System\IO\RowConfigReader.cs"
              Link="Common\System\IO\RowConfigReader.cs" />
+    <Compile Include="$(CommonPath)System\HexConverter.cs"
+             Link="Common\System\HexConverter.cs" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="LoggingTest.cs" />

src/libraries/System.Private.CoreLib/src/Resources/Strings.resx

@@ -2224,6 +2224,12 @@
   <data name="Format_NoFormatSpecifier" xml:space="preserve">
     <value>No format specifiers were provided.</value>
   </data>
+  <data name="Format_BadHexChar" xml:space="preserve">
+    <value>The input is not a valid hex string as it contains a non-hex character.</value>
+  </data>
+  <data name="Format_BadHexLength" xml:space="preserve">
+    <value>The input is not a valid hex string as its length is not a multiple of 2.</value>
+  </data>
   <data name="Format_BadQuote" xml:space="preserve">
     <value>Cannot find a matching quote character for the character '{0}'.</value>
   </data>