From 490af521478771fc598515000142144a1d3a22fa Mon Sep 17 00:00:00 2001
From: Tom Deakin <tom.deakin@bristol.ac.uk>
Date: Wed, 3 Feb 2021 10:54:33 +0000
Subject: [PATCH] Add nstream to C++ STD version -- untested as compilers not
 ready

---
 STD20Stream.cpp | 14 ++++++++++++++
 STD20Stream.hpp |  1 +
 STDStream.cpp   | 11 +++++++++++
 STDStream.h     |  1 +
 4 files changed, 27 insertions(+)

diff --git a/STD20Stream.cpp b/STD20Stream.cpp
index 09f83d4..8290033 100644
--- a/STD20Stream.cpp
+++ b/STD20Stream.cpp
@@ -94,6 +94,20 @@ void STD20Stream<T>::triad()
   );
 }
 
+template <class T>
+void STD20Stream<T>::nstream()
+{
+  const T scalar = startScalar;
+
+  std::for_each_n(
+    std::execution::par_unseq,
+    std::views::iota(0).begin(), array_size,
+    [&] (int i) {
+      a[i] += b[i] + scalar * c[i];
+    }
+  );
+}
+
 template <class T>
 T STD20Stream<T>::dot()
 {
diff --git a/STD20Stream.hpp b/STD20Stream.hpp
index a8a3c4f..e5daa3c 100644
--- a/STD20Stream.hpp
+++ b/STD20Stream.hpp
@@ -33,6 +33,7 @@ class STD20Stream : public Stream<T>
     virtual void add() override;
     virtual void mul() override;
     virtual void triad() override;
+    virtual void nstream() override;
     virtual T dot() override;
 
     virtual void init_arrays(T initA, T initB, T initC) override;
diff --git a/STDStream.cpp b/STDStream.cpp
index cd966ae..30ad420 100644
--- a/STDStream.cpp
+++ b/STDStream.cpp
@@ -72,6 +72,17 @@ void STDStream<T>::triad()
   std::transform(exe_policy, b, b+array_size, c, a, [](T bi, T ci){ return bi+startScalar*ci; });
 }
 
+template <class T>
+void STDStream<T>::nstream()
+{
+  //  a[i] += b[i] + scalar * c[i];
+  //  Need to do in two stages with C++11 STL.
+  //  1: a[i] += b[i]
+  //  2: a[i] += scalar * c[i];
+  std::transform(exe_policy, a, a+array_size, b, a, [](T ai, T bi){ return ai + bi; });
+  std::transform(exe_policy, a, a+array_size, c, a, [](T ai, T ci){ return ai + startScalar*ci; });
+}
+
 template <class T>
 T STDStream<T>::dot()
 {
diff --git a/STDStream.h b/STDStream.h
index 538f857..9ff7800 100644
--- a/STDStream.h
+++ b/STDStream.h
@@ -31,6 +31,7 @@ class STDStream : public Stream<T>
     virtual void add() override;
     virtual void mul() override;
     virtual void triad() override;
+    virtual void nstream() override;
     virtual T dot() override;
 
     virtual void init_arrays(T initA, T initB, T initC) override;