[OTLP] Refactor ProtobufSerializer.WriteReservedLength() to improve performance (#6367)

Directory.Packages.props

@@ -83,7 +83,7 @@
       These packages are referenced as "PrivateAssets" or used in tests/examples.
   -->
   <ItemGroup>
-    <PackageVersion Include="BenchmarkDotNet" Version="[0.13.12,0.14)" />
+    <PackageVersion Include="BenchmarkDotNet" Version="0.15.2" />
     <PackageVersion Include="CommandLineParser" Version="[2.9.1,3.0)" />
     <PackageVersion Include="GitHubActionsTestLogger" Version="2.4.1" />
     <PackageVersion Include="Grpc.AspNetCore" Version="[2.59.0,3.0)" />

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ExportClient/Grpc/GrpcStatusDeserializer.cs

@@ -201,8 +201,8 @@ internal static class GrpcStatusDeserializer
                 throw new EndOfStreamException();
             }
 
-            result |= (long)(b & 0x7F) << shift;
+            result |= (long)(b & 0b_0111_1111) << shift;
-            if ((b & 0x80) == 0)
+            if ((b & 0b_1000_0000) == 0)
             {
                 return result;
             }

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/Serializer/ProtobufSerializer.cs

@@ -18,6 +18,8 @@ internal static class ProtobufSerializer
     private const ulong ULong128 = 0x80;
     private const int Fixed32Size = 4;
     private const int Fixed64Size = 8;
+    private const int MaskBitsLow = 0b_0111_1111;
+    private const int MaskBitHigh = 0b_1000_0000;
 
     private static readonly Encoding Utf8Encoding = Encoding.UTF8;
 
@@ -42,63 +44,11 @@ internal static class ProtobufSerializer
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     internal static void WriteReservedLength(byte[] buffer, int writePosition, int length)
     {
-        int byteLength = 0;
+        var slice = buffer.AsSpan(writePosition, 4);
-        int? firstByte = null;
+        slice[0] = (byte)((length & MaskBitsLow) | MaskBitHigh);
-        int? secondByte = null;
+        slice[1] = (byte)(((length >> 7) & MaskBitsLow) | MaskBitHigh);
-        int? thirdByte = null;
+        slice[2] = (byte)(((length >> 14) & MaskBitsLow) | MaskBitHigh);
-        int? fourthByte = null;
+        slice[3] = (byte)((length >> 21) & MaskBitsLow);
-
-        do
-        {
-            switch (byteLength)
-            {
-                case 0:
-                    firstByte = length & 0x7F;
-                    break;
-                case 1:
-                    secondByte = length & 0x7F;
-                    break;
-                case 2:
-                    thirdByte = length & 0x7F;
-                    break;
-                case 3:
-                    fourthByte = length & 0x7F;
-                    break;
-            }
-
-            length >>= 7;
-            byteLength++;
-        }
-        while (length > 0);
-
-        if (fourthByte.HasValue)
-        {
-            buffer[writePosition++] = (byte)(firstByte!.Value | 0x80);
-            buffer[writePosition++] = (byte)(secondByte!.Value | 0x80);
-            buffer[writePosition++] = (byte)(thirdByte!.Value | 0x80);
-            buffer[writePosition++] = (byte)fourthByte!.Value;
-        }
-        else if (thirdByte.HasValue)
-        {
-            buffer[writePosition++] = (byte)(firstByte!.Value | 0x80);
-            buffer[writePosition++] = (byte)(secondByte!.Value | 0x80);
-            buffer[writePosition++] = (byte)(thirdByte!.Value | 0x80);
-            buffer[writePosition++] = 0;
-        }
-        else if (secondByte.HasValue)
-        {
-            buffer[writePosition++] = (byte)(firstByte!.Value | 0x80);
-            buffer[writePosition++] = (byte)(secondByte!.Value | 0x80);
-            buffer[writePosition++] = 0x80;
-            buffer[writePosition++] = 0;
-        }
-        else
-        {
-            buffer[writePosition++] = (byte)(firstByte!.Value | 0x80);
-            buffer[writePosition++] = 0x80;
-            buffer[writePosition++] = 0x80;
-            buffer[writePosition++] = 0;
-        }
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -171,7 +121,7 @@ internal static class ProtobufSerializer
     {
         while (value >= UInt128)
         {
-            buffer[writePosition++] = (byte)(0x80 | (value & 0x7F));
+            buffer[writePosition++] = (byte)(MaskBitHigh | (value & MaskBitsLow));
             value >>= 7;
         }
 
@@ -184,7 +134,7 @@ internal static class ProtobufSerializer
     {
         while (value >= ULong128)
         {
-            buffer[writePosition++] = (byte)(0x80 | (value & 0x7F));
+            buffer[writePosition++] = (byte)(MaskBitHigh | (value & MaskBitsLow));
             value >>= 7;
         }