Address perf+correctness of StrLen and StrChr

.vscode/launch.json

@@ -10,7 +10,7 @@
             "request": "launch",
             "preLaunchTask": "build",
             // If you have changed target frameworks, make sure to update the program path.
-            "program": "${workspaceFolder}/Cesium.Compiler/bin/Debug/net6.0/Cesium.Compiler.dll",
+            "program": "${workspaceFolder}/Cesium.Compiler/bin/Debug/net7.0/Cesium.Compiler.dll",
             "args": [],
             "cwd": "${workspaceFolder}/Cesium.Compiler",
             // For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
@@ -23,4 +23,4 @@
             "request": "attach"
         }
     ]
-}
+}

Cesium.Compiler/Compilation.cs

@@ -141,7 +141,7 @@ private static void SaveAssembly(
         {
             var runtimeConfigFilePath = Path.ChangeExtension(outputFilePath, "runtimeconfig.json");
             Console.WriteLine($"Generating a .NET 6 runtime config at {runtimeConfigFilePath}.");
-            File.WriteAllText(runtimeConfigFilePath, RuntimeConfig.EmitNet6());
+            File.WriteAllText(runtimeConfigFilePath, RuntimeConfig.EmitNet7());
         }
     }
 }

Cesium.Compiler/RuntimeConfig.cs

@@ -2,19 +2,6 @@ namespace Cesium.Compiler;
 
 internal static class RuntimeConfig
 {
-    public static string EmitNet6() => """
-    {
-      "runtimeOptions": {
-        "tfm": "net6.0",
-        "rollForward": "Major",
-        "framework": {
-          "name": "Microsoft.NETCore.App",
-          "version": "6.0.0"
-        }
-      }
-    }
-    """.ReplaceLineEndings("\n");
-
     public static string EmitNet7() => """
     {
       "runtimeOptions": {

Cesium.Runtime.Tests/Cesium.Runtime.Tests.csproj

@@ -2,7 +2,7 @@
 
     <PropertyGroup>
         <TargetFrameworks>net7.0</TargetFrameworks>
-        <TargetFrameworks Condition=" $([MSBuild]::IsOsPlatform('Windows')) ">$(TargetFrameworks);net48</TargetFrameworks>
+        <!-- <TargetFrameworks Condition=" $([MSBuild]::IsOsPlatform('Windows')) ">$(TargetFrameworks);net48</TargetFrameworks> -->
         <ImplicitUsings>enable</ImplicitUsings>
         <IsPackable>false</IsPackable>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

Cesium.Runtime.Tests/StringFunctionTests.cs

@@ -0,0 +1,75 @@
+using System.Text;
+
+namespace Cesium.Runtime.Tests;
+
+public unsafe class StringFunctionTests
+{
+    [Theory]
+    [InlineData("Hello\0", 5)]
+    [InlineData("Goodbye\0", 7)]
+    [InlineData("Hello\0Goodbye\0", 5)]
+    [InlineData("                  \0", 18)]
+    public void StrLen(string input, int expected)
+    {
+        // TODO: If you are rich enough to procure a 2-4+ GB RAM runner,
+        // please update this test to exercise the path where the string
+        // length exceeds int.MaxLength of bytes.
+        var bytes = Encoding.UTF8.GetBytes(input);
+        fixed (byte* str = bytes)
+        {
+            var actual = StringFunctions.StrLen(str);
+
+            Assert.Equal((nuint)expected, actual);
+        }
+    }
+
+    [Fact]
+    public void StrLen_Null()
+    {
+        var actual = StringFunctions.StrLen(null);
+
+        Assert.Equal((nuint)0, actual);
+    }
+
+    [Theory]
+    [InlineData("Hello\n", 5)]
+    [InlineData("Goodbye\n", 7)]
+    [InlineData("Hello\nGoodbye\n", 5)]
+    [InlineData("                  \n", 18)]
+    public void StrChr(string input, int expectedOffset)
+    {
+        var needle = '\n';
+        var bytes = Encoding.UTF8.GetBytes(input);
+        fixed (byte* str = bytes)
+        {
+            var ptr = StringFunctions.StrChr(str, '\n');
+
+            Assert.Equal((byte)needle, *ptr);
+            Assert.Equal(expectedOffset, (int)(ptr - str));
+        }
+    }
+
+    [Theory]
+    [InlineData("Hello\0")]
+    [InlineData("Goodbye\0")]
+    [InlineData("Hello Goodbye\0")]
+    [InlineData("                  \0")]
+    public void StrChr_NotFound(string input)
+    {
+        var bytes = Encoding.UTF8.GetBytes(input);
+        fixed (byte* str = bytes)
+        {
+            var actual = StringFunctions.StrChr(str, '\n');
+
+            Assert.True(actual is null);
+        }
+    }
+
+    [Fact]
+    public void StrChr_Null()
+    {
+        var actual = StringFunctions.StrChr(null, '\0');
+
+        Assert.True(actual is null);
+    }
+}

Cesium.Runtime/Cesium.Runtime.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
+    <TargetFramework>net7.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>

Cesium.Runtime/StringFunctions.cs

@@ -1,9 +1,7 @@
-#if NETSTANDARD
-using System.Text;
-#else
-using System.Collections.Specialized;
-using System.Runtime.InteropServices;
-#endif
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.Arm;
 
 namespace Cesium.Runtime;
 
@@ -14,50 +12,57 @@ public static unsafe class StringFunctions
 {
     public static nuint StrLen(byte* str)
     {
-#if NETSTANDARD
-        if (str == null)
+        if (str != null)
         {
-            return 0;
-        }
+            var start = str;
+            while ((nuint)str % 16 != 0)
+            {
+                if (*str is 0)
+                {
+                    goto Done;
+                }
+                str++;
+            }
 
-        Encoding encoding = Encoding.UTF8;
-        int byteLength = 0;
-        byte* search = str;
-        while (*search != '\0')
-        {
-            byteLength++;
-            search++;
+            while (true)
+            {
+                var eqmask = Vector128.Equals(
+                    Vector128.LoadAligned(str),
+                    Vector128<byte>.Zero);
+                if (eqmask == Vector128<byte>.Zero)
+                {
+                    str += Vector128<byte>.Count;
+                    continue;
+                }
+
+                str += IndexOfMatch(eqmask);
+                break;
+            }
+        Done:
+            return (nuint)str - (nuint)start;
         }
 
-        int stringLength = encoding.GetCharCount(str, byteLength);
-        return (uint)stringLength;
-#else
-        return (uint)(Marshal.PtrToStringUTF8((nint)str)?.Length ?? 0);
-#endif
+        return 0;
     }
     public static byte* StrCpy(byte* dest, byte* src)
     {
-        if (dest == null)
+        if (dest != null)
         {
-            return null;
-        }
+            var result = dest;
+            if (src != null)
+            {
+                // SIMD scan into SIMD copy (traversing the data twice)
+                // is much faster than a single scalar check+copy loop.
+                var length = StrLen(src);
+                Buffer.MemoryCopy(src, dest, length, length);
+                dest += length;
+            }
 
-        var result = dest;
-        if (src == null)
-        {
+            *dest = 0;
             return dest;
         }
 
-        byte* search = src;
-        while (*search != '\0')
-        {
-            *dest = *search;
-            search++;
-            dest++;
-        }
-
-        *dest = 0;
-        return result;
+        return null;
     }
     public static byte* StrNCpy(byte* dest, byte* src, nuint count)
     {
@@ -186,21 +191,50 @@ public static int StrNCmp(byte* lhs, byte* rhs, nuint count)
     }
     public static byte* StrChr(byte* str, int ch)
     {
-        if (str == null)
+        if (str != null)
         {
-            return null;
-        }
+            byte c = (byte)ch;
 
-        while (*str != 0)
-        {
-            if (*str == ch)
+            while ((nuint)str % 16 != 0)
             {
-                return str;
+                var curr = *str;
+                if (curr == c)
+                {
+                    goto Done;
+                }
+                else if (curr == 0)
+                {
+                    goto NotFound;
+                }
+                str++;
             }
 
-            str++;
+            var element = Vector128.Create(c);
+            var nullByte = Vector128<byte>.Zero;
+            while (true)
+            {
+                var chars = Vector128.LoadAligned(str);
+                var eqmask = Vector128.Equals(chars, element) |
+                             Vector128.Equals(chars, nullByte);
+                if (eqmask == Vector128<byte>.Zero)
+                {
+                    str += Vector128<byte>.Count;
+                    continue;
+                }
+
+                str += IndexOfMatch(eqmask);
+                if (*str == 0)
+                {
+                    goto NotFound;
+                }
+                break;
+            }
+
+        Done:
+            return str;
         }
 
+    NotFound:
         return null;
     }
 
@@ -215,7 +249,6 @@ public static int StrCmp(byte* lhs, byte* rhs)
             if (*lhs > *rhs) return 1;
         }
 
-
         if (*lhs < *rhs) return -1;
         if (*lhs > *rhs) return 1;
         return 0;
@@ -253,4 +286,20 @@ public static int MemCmp(void* lhs, void* rhs, nuint count)
 
         return 0;
     }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    static uint IndexOfMatch(Vector128<byte> eqmask)
+    {
+        if (AdvSimd.Arm64.IsSupported)
+        {
+            var res = AdvSimd
+                .ShiftRightLogicalNarrowingLower(eqmask.AsUInt16(), 4)
+                .AsUInt64()
+                .ToScalar();
+            return (uint)BitOperations.TrailingZeroCount(res) >> 2;
+        }
+
+        return (uint)BitOperations.TrailingZeroCount(
+            eqmask.ExtractMostSignificantBits());
+    }
 }

Cesium.Test.Framework/CSharpCompilationUtil.cs

@@ -11,7 +11,7 @@ public static class CSharpCompilationUtil
     public static readonly TargetRuntimeDescriptor DefaultRuntime = TargetRuntimeDescriptor.Net60;
     private const string _configuration = "Debug";
     private const string _targetRuntime = "net7.0";
-    private const string _cesiumRuntimeLibTargetRuntime = "net6.0";
+    private const string _cesiumRuntimeLibTargetRuntime = "net7.0";
     private const string _projectName = "TestProject";
 
     /// <summary>Semaphore that controls the amount of simultaneously running tests.</summary>