IVGCVSW-3694 Add ArgMinMax implementation for Ref

 * Add ArgMinMax implementation
 * Add utility function to get number of elements between axis
 * Add utility function to get unsigned axis
 * Unit tests for ArgMinMax function

Signed-off-by: Narumol Prangnawarat <narumol.prangnawarat@arm.com>
Change-Id: I7bc3d610dda9526190187eb87394a8ed7a4b5cdd
diff --git a/src/backends/reference/workloads/ArgMinMax.hpp b/src/backends/reference/workloads/ArgMinMax.hpp
new file mode 100644
index 0000000..5a9c6a8
--- /dev/null
+++ b/src/backends/reference/workloads/ArgMinMax.hpp
@@ -0,0 +1,20 @@
+//
+// Copyright © 2019 Arm Ltd. All rights reserved.
+// SPDX-License-Identifier: MIT
+//
+
+#pragma once
+
+#include "armnn/Tensor.hpp"
+#include "armnn/Descriptors.hpp"
+
+#include "Decoders.hpp"
+
+namespace armnn
+{
+
+void ArgMinMax(Decoder<float>& in, int32_t* out, const TensorInfo& inputTensorInfo,
+               const TensorInfo& outputTensorInfo, ArgMinMaxFunction function, int axis);
+
+} //namespace armnn
+