1 files changed, 48 insertions, 0 deletions
diff --git a/src/mscorlib/src/System/Text/StringBuilder.CoreCLR.cs b/src/mscorlib/src/System/Text/StringBuilder.CoreCLR.cs
new file mode 100644
index 0000000000..db3895f161
--- /dev/null
+++ b/src/mscorlib/src/System/Text/StringBuilder.CoreCLR.cs
@@ -0,0 +1,48 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// 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.Runtime.CompilerServices;
+
+namespace System.Text
+{
+    public partial class StringBuilder
+    {
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        internal unsafe extern void ReplaceBufferInternal(char* newBuffer, int newLength);
+
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        internal unsafe extern void ReplaceBufferAnsiInternal(sbyte* newBuffer, int newLength);
+
+        // Copies the source StringBuilder to the destination IntPtr memory allocated with len bytes.
+        internal unsafe void InternalCopy(IntPtr dest, int len)
+        {
+            if (len == 0)
+                return;
+
+            bool isLastChunk = true;
+            byte* dstPtr = (byte*)dest.ToPointer();
+            StringBuilder currentSrc = FindChunkForByte(len);
+
+            do
+            {
+                int chunkOffsetInBytes = currentSrc.m_ChunkOffset * sizeof(char);
+                int chunkLengthInBytes = currentSrc.m_ChunkLength * sizeof(char);
+                fixed (char* charPtr = &currentSrc.m_ChunkChars[0])
+                {
+                    byte* srcPtr = (byte*)charPtr;
+                    if (isLastChunk)
+                    {
+                        isLastChunk = false;
+                        Buffer.Memcpy(dstPtr + chunkOffsetInBytes, srcPtr, len - chunkOffsetInBytes);
+                    }
+                    else
+                    {
+                        Buffer.Memcpy(dstPtr + chunkOffsetInBytes, srcPtr, chunkLengthInBytes);
+                    }
+                }
+                currentSrc = currentSrc.m_ChunkPrevious;
+            } while (currentSrc != null);
+        }
+    }
+}