From 47690d6a7bb410ef5f268d0bea8a7bbc3ed89474 Mon Sep 17 00:00:00 2001
From: liaogang <liaogang@baidu.com>
Date: Tue, 1 Aug 2017 15:50:21 +0800
Subject: [PATCH] ENH: Add EigenScalar

---
 paddle/framework/eigen.h       | 16 ++++++++++++++++
 paddle/framework/eigen_test.cc | 11 +++++++++++
 paddle/operators/type_alias.h  |  4 ++++
 3 files changed, 31 insertions(+)

diff --git a/paddle/framework/eigen.h b/paddle/framework/eigen.h
index 5f3358c69..a4667cc51 100644
--- a/paddle/framework/eigen.h
+++ b/paddle/framework/eigen.h
@@ -80,5 +80,21 @@ struct EigenVector : public EigenTensor<T, 1, MajorType, IndexType> {
   }
 };
 
+template <typename T, int MajorType = Eigen::RowMajor,
+          typename IndexType = Eigen::DenseIndex>
+struct EigenScalar {
+  // Scalar tensor (implemented as a rank-0 tensor) of scalar type T.
+  using Type = Eigen::TensorMap<
+      Eigen::TensorFixedSize<T, Eigen::Sizes<>, MajorType, IndexType>>;
+  using ConstType = Eigen::TensorMap<
+      Eigen::TensorFixedSize<const T, Eigen::Sizes<>, MajorType, IndexType>>;
+
+  static Type From(Tensor& tensor) { return Type(tensor.data<T>()); }
+
+  static ConstType From(const Tensor& tensor) {
+    return ConstType(tensor.data<T>());
+  }
+};
+
 }  // namespace framework
 }  // namespace paddle
diff --git a/paddle/framework/eigen_test.cc b/paddle/framework/eigen_test.cc
index a9fa728e4..dc1957691 100644
--- a/paddle/framework/eigen_test.cc
+++ b/paddle/framework/eigen_test.cc
@@ -46,6 +46,17 @@ TEST(Eigen, Tensor) {
   }
 }
 
+TEST(Eigen, ScalarFrom) {
+  Tensor t;
+  int* p = t.mutable_data<int>(make_ddim({1}), platform::CPUPlace());
+  *p = static_cast<int>(100);
+
+  EigenScalar<int>::Type es = EigenScalar<int>::From(t);
+
+  ASSERT_EQ(0, es.dimension(0));
+  ASSERT_EQ(100, es(0));
+}
+
 TEST(Eigen, VectorFrom) {
   Tensor t;
   float* p = t.mutable_data<float>(make_ddim({6}), platform::CPUPlace());
diff --git a/paddle/operators/type_alias.h b/paddle/operators/type_alias.h
index b712e457f..275c0c1ac 100644
--- a/paddle/operators/type_alias.h
+++ b/paddle/operators/type_alias.h
@@ -23,6 +23,10 @@ namespace operators {
 
 using OpKernel = framework::OpKernel;
 using KernelContext = framework::KernelContext;
+template <typename T,
+          int MajorType = Eigen::RowMajor,
+          typename IndexType = Eigen::DenseIndex>
+using EigenScalar = framework::EigenScalar<T, MajorType, IndexType>;
 template <typename T,
           int MajorType = Eigen::RowMajor,
           typename IndexType = Eigen::DenseIndex>
-- 
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