From 46f88fc454e78484ebdf9d58990d0489c1103cf4 Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <rmlarsen@google.com>
Date: Tue, 11 Sep 2018 10:08:10 -0700
Subject: Use numerically stable tree reduction in TensorReduction.

---
 .../Eigen/CXX11/src/Tensor/TensorFunctors.h        | 68 ++++++++++------------
 1 file changed, 30 insertions(+), 38 deletions(-)

(limited to 'unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h')

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h b/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h
index cd666c173..9fd276075 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorFunctors.h
@@ -58,16 +58,15 @@ template<typename Reducer, typename Device>
 struct reducer_traits {
   enum {
     Cost = 1,
-    PacketAccess = false
+    PacketAccess = false,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
 // Standard reduction functors
 template <typename T> struct SumReducer
 {
-  static const bool PacketAccess = packet_traits<T>::HasAdd;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(const T t, T* accum) const {
     internal::scalar_sum_op<T> sum_op;
     *accum = sum_op(*accum, t);
@@ -103,16 +102,14 @@ template <typename T, typename Device>
 struct reducer_traits<SumReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::AddCost,
-    PacketAccess = PacketType<T, Device>::HasAdd
+    PacketAccess = PacketType<T, Device>::HasAdd,
+    IsStateful = false,
+    IsExactlyAssociative = NumTraits<T>::IsInteger
   };
 };
 
-
 template <typename T> struct MeanReducer
 {
-  static const bool PacketAccess = packet_traits<T>::HasAdd && packet_traits<T>::HasDiv && !NumTraits<T>::IsInteger;
-  static const bool IsStateful = true;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE
   MeanReducer() : scalarCount_(0), packetCount_(0) { }
 
@@ -161,7 +158,9 @@ template <typename T, typename Device>
 struct reducer_traits<MeanReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::AddCost,
-    PacketAccess = PacketType<T, Device>::HasAdd
+    PacketAccess = PacketType<T, Device>::HasAdd && !NumTraits<T>::IsInteger,
+    IsStateful = true,
+    IsExactlyAssociative = NumTraits<T>::IsInteger
   };
 };
 
@@ -194,9 +193,6 @@ struct MinMaxBottomValue<T, false, false> {
 
 template <typename T> struct MaxReducer
 {
-  static const bool PacketAccess = packet_traits<T>::HasMax;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(const T t, T* accum) const {
     if (t > *accum) { *accum = t; }
   }
@@ -228,16 +224,15 @@ template <typename T, typename Device>
 struct reducer_traits<MaxReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::AddCost,
-    PacketAccess = PacketType<T, Device>::HasMax
+    PacketAccess = PacketType<T, Device>::HasMax,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
 
 template <typename T> struct MinReducer
 {
-  static const bool PacketAccess = packet_traits<T>::HasMin;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(const T t, T* accum) const {
     if (t < *accum) { *accum = t; }
   }
@@ -269,16 +264,15 @@ template <typename T, typename Device>
 struct reducer_traits<MinReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::AddCost,
-    PacketAccess = PacketType<T, Device>::HasMin
+    PacketAccess = PacketType<T, Device>::HasMin,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
 
 template <typename T> struct ProdReducer
 {
-  static const bool PacketAccess = packet_traits<T>::HasMul;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(const T t, T* accum) const {
     internal::scalar_product_op<T> prod_op;
     (*accum) = prod_op(*accum, t);
@@ -314,16 +308,15 @@ template <typename T, typename Device>
 struct reducer_traits<ProdReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::MulCost,
-    PacketAccess = PacketType<T, Device>::HasMul
+    PacketAccess = PacketType<T, Device>::HasMul,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
 
 struct AndReducer
 {
-  static const bool PacketAccess = false;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(bool t, bool* accum) const {
     *accum = *accum && t;
   }
@@ -339,15 +332,14 @@ template <typename Device>
 struct reducer_traits<AndReducer, Device> {
   enum {
     Cost = 1,
-    PacketAccess = false
+    PacketAccess = false,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
 
 struct OrReducer {
-  static const bool PacketAccess = false;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(bool t, bool* accum) const {
     *accum = *accum || t;
   }
@@ -363,7 +355,9 @@ template <typename Device>
 struct reducer_traits<OrReducer, Device> {
   enum {
     Cost = 1,
-    PacketAccess = false
+    PacketAccess = false,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
@@ -371,9 +365,6 @@ struct reducer_traits<OrReducer, Device> {
 // Argmin/Argmax reducers
 template <typename T> struct ArgMaxTupleReducer
 {
-  static const bool PacketAccess = false;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(const T t, T* accum) const {
     if (t.second > accum->second) { *accum = t; }
   }
@@ -389,16 +380,15 @@ template <typename T, typename Device>
 struct reducer_traits<ArgMaxTupleReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::AddCost,
-    PacketAccess = false
+    PacketAccess = false,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
 
 template <typename T> struct ArgMinTupleReducer
 {
-  static const bool PacketAccess = false;
-  static const bool IsStateful = false;
-
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE void reduce(const T& t, T* accum) const {
     if (t.second < accum->second) { *accum = t; }
   }
@@ -414,7 +404,9 @@ template <typename T, typename Device>
 struct reducer_traits<ArgMinTupleReducer<T>, Device> {
   enum {
     Cost = NumTraits<T>::AddCost,
-    PacketAccess = false
+    PacketAccess = false,
+    IsStateful = false,
+    IsExactlyAssociative = true
   };
 };
 
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