follow example for creating 'dot' function

Author: kevinushey

examples/boost-simd-dot.cpp

@@ -0,0 +1,65 @@
+// [[Rcpp::depends(RcppParallel)]]
+#include <RcppParallel.h>
+#include <Rcpp.h>
+using namespace Rcpp;
+
+// http://nt2.metascale.fr/doc/html/tutorials/processing_data_the_simd_way.html
+#include <boost/simd/memory/allocator.hpp>
+#include <boost/simd/sdk/simd/pack.hpp>
+#include <boost/simd/include/functions/sum.hpp>
+#include <boost/simd/include/functions/load.hpp>
+#include <boost/simd/include/functions/plus.hpp>
+#include <boost/simd/include/functions/multiplies.hpp>
+
+template <typename Value>
+Value simd_dot(Value* first1, Value* last1, Value* first2)
+{
+   using boost::simd::sum;
+   using boost::simd::pack;
+   using boost::simd::load;
+   
+   typedef pack<Value> type;
+   type tmp;
+   
+   // Let's consider that (last1-first1) is divisible by the size of the pack.
+   while (first1 != last1)
+   {
+      // Load current values from the datasets
+      pack<Value> x1 = load<type>(first1);
+      pack<Value> x2 = load<type>(first2);
+      
+      // Computation
+      tmp = tmp + x1 * x2;
+      
+      // Advance to the next SIMD vector
+      first1 += type::static_size;
+      first2 += type::static_size;
+   }
+   
+   return sum(tmp);
+}
+
+// [[Rcpp::export]]
+double dot(NumericVector lhs, NumericVector rhs)
+{
+   // construct simd vectors
+   typedef std::vector< double, boost::simd::allocator<double> > vector_t;
+   vector_t a(lhs.begin(), lhs.end());
+   vector_t b(rhs.begin(), rhs.end());
+   
+   // call dot function
+   double result = simd_dot(
+      &a[0],
+      &a[0] + a.size(),
+      &b[0]
+   );
+   
+   return result;
+}
+
+/*** R
+lhs <- rnorm(10)
+rhs <- rnorm(10)
+result <- dot(lhs, rhs)
+all.equal(result, sum(lhs * rhs))
+*/

examples/boost-simd-hello-world.cpp

@@ -24,3 +24,7 @@ void HelloWorld()
 
    Rcout << res << std::endl;
 }
+
+/*** R
+HelloWorld()
+*/