Optimize remainder

protocolbuffers · Dec 16, 2020 · 21f9dd5 · 21f9dd5
1 parent 83bfa4c
commit 21f9dd5
Showing 1 changed file with 11 additions and 7 deletions.
diff --git a/csharp/src/Google.Protobuf/WritingPrimitives.cs b/csharp/src/Google.Protobuf/WritingPrimitives.cs
@@ -179,8 +179,6 @@ public static void WriteString(ref Span<byte> buffer, ref WriterInternalState st
             {
                 if (length == value.Length) // Must be all ASCII...
                 {
-                    int currentIndex = 0;
-
                     // If 64bit, and value has at least 4 chars, process 4 chars at a time.
                     if (IntPtr.Size == 8 && value.Length >= 4)
                     {
@@ -190,6 +188,7 @@ public static void WriteString(ref Span<byte> buffer, ref WriterInternalState st
                         // Process 4 chars at a time until there are less than 4 remaining.
                         // We already know all characters are ASCII so there is no need to validate the source.
                         int lastIndexWhereCanReadFourChars = value.Length - 4;
+                        int currentIndex = 0;
                         do
                         {
                             NarrowFourUtf16CharsToAsciiAndWriteToBuffer(
@@ -198,14 +197,19 @@ public static void WriteString(ref Span<byte> buffer, ref WriterInternalState st
 
                         } while ((currentIndex += 4) <= lastIndexWhereCanReadFourChars);
 
-                        // Any chars remaining are processed in for loop below.
+                        // Process remainder.
+                        for (; currentIndex < length; currentIndex++)
+                        {
+                            Unsafe.AddByteOffset(ref destinationBytes, (IntPtr)currentIndex) = Unsafe.AddByteOffset(ref sourceBytes, (IntPtr)(currentIndex * 2));
+                        }
                     }
-
-                    for (int i = currentIndex; i < length; i++)
+                    else
                     {
-                        buffer[state.position + i] = (byte)value[i];
+                        for (int i = 0; i < length; i++)
+                        {
+                            buffer[state.position + i] = (byte)value[i];
+                        }
                     }
-
                     state.position += length;
                 }
                 else