Tensor.Creation: Perf-opted when creating tensor from NDArray of string

src/TensorFlowNET.Core/Tensors/Tensor.Creation.cs

@@ -21,6 +21,7 @@ using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
+using NumSharp.Backends;
 using NumSharp.Backends.Unmanaged;
 using static Tensorflow.c_api;
 
@@ -477,7 +478,7 @@ namespace Tensorflow
 
             IntPtr tensor = c_api.TF_TensorData(handle);
             Marshal.WriteInt64(tensor, 0);
-            fixed (byte* src = &buffer[0])
+            fixed (byte* src = buffer)
                 c_api.TF_StringEncode(src, (UIntPtr)buffer.Length, (sbyte*)(tensor + sizeof(Int64)), size, status);
             _handle = handle;
             status.Check(true);
@@ -486,24 +487,45 @@ namespace Tensorflow
         public unsafe Tensor(NDArray nd, TF_DataType? tensorDType = null)
         {
             // todo: handle nd of type "String" here too
-            if (tensorDType == TF_DataType.TF_STRING && nd.dtype.Name == "Byte")
+            if (tensorDType == TF_DataType.TF_STRING && nd.typecode == NPTypeCode.Byte)
             {
-                var buffer = nd.ToArray<byte>();
-                var size = c_api.TF_StringEncodedSize((UIntPtr)buffer.Length);
-                var handle = TF_AllocateTensor(TF_DataType.TF_STRING, IntPtr.Zero, 0, (UIntPtr)((ulong)size + 8));
-
-                IntPtr tensor = c_api.TF_TensorData(handle);
-                Marshal.WriteInt64(tensor, 0);
+                if (nd.Unsafe.Storage.Shape.IsContiguous)
+                {
+                    var bytesLength = (UIntPtr)nd.size;
+                    var size = c_api.TF_StringEncodedSize(bytesLength);
+                    var handle = TF_AllocateTensor(TF_DataType.TF_STRING, IntPtr.Zero, 0, (UIntPtr) ((ulong) size + 8));
+
+                    IntPtr tensor = c_api.TF_TensorData(handle);
+                    Marshal.WriteInt64(tensor, 0);
+
+                    var status = new Status();
+                    c_api.TF_StringEncode((byte*) nd.Unsafe.Address, bytesLength, (sbyte*) (tensor + sizeof(Int64)), size, status);
+
+                    status.Check(true);
+                    _handle = handle;
+                    IsMemoryOwner = false;
+                } 
+                else
+                {
+                    var buffer = nd.ToArray<byte>();
+                    var size = c_api.TF_StringEncodedSize((UIntPtr) buffer.Length);
+                    var handle = TF_AllocateTensor(TF_DataType.TF_STRING, IntPtr.Zero, 0, (UIntPtr) ((ulong) size + 8));
+
+                    IntPtr tensor = c_api.TF_TensorData(handle);
+                    Marshal.WriteInt64(tensor, 0);
+
+                    var status = new Status();
+                    fixed (byte* src = buffer)
+                        c_api.TF_StringEncode(src, (UIntPtr) buffer.Length, (sbyte*) (tensor + sizeof(Int64)), size, status);
+
+                    status.Check(true);
+                    _handle = handle;
+                    IsMemoryOwner = false;
+                }
 
-                var status = new Status();
-                fixed (byte* src = &buffer[0])
-                    c_api.TF_StringEncode(src, (UIntPtr)buffer.Length, (sbyte*)(tensor + sizeof(Int64)), size, status);
-
-                status.Check(true);
-                _handle=handle;
-                IsMemoryOwner = false;
                 return;
             }
+
             _handle = CreateTensorFromNDArray(nd, tensorDType);
             IsMemoryOwner = true;
         }