add 'for_each' helper algorithm

Author: kevinushey

examples/boost-simd-for-each.cpp

@@ -0,0 +1,38 @@
+// [[Rcpp::depends(RcppParallel)]]
+#define RCPP_PARALLEL_USE_SIMD
+#include <RcppParallel.h>
+#include <Rcpp.h>
+using namespace Rcpp;
+
+// Product of squared deviations
+class Accumulator
+{
+public:
+   
+   Accumulator() : result_(1.0) {}
+   
+   template <typename T>
+   void operator()(const T& data)
+   {
+      result_ *= boost::simd::prod(data);
+   }
+   
+   operator double() const {
+      return result_;
+   }
+   
+private:
+   double result_;
+};
+
+// [[Rcpp::export]]
+double vectorProd(NumericVector x) {
+   auto accumulator = Accumulator();
+   boost::simd::for_each(x.begin(), x.end(), accumulator);
+   return accumulator;
+}
+
+/*** R
+x <- 1:16
+vectorProd(x)
+*/

inst/include/RcppParallel/SIMD.h

@@ -38,5 +38,6 @@
 #include <RcppParallel/simd/adaptors.h>
 
 #include <RcppParallel/simd/map_reduce.h>
+#include <RcppParallel/simd/for_each.h>
 
 #endif /* RCPP_PARALLEL_SIMD_H */

inst/include/RcppParallel/simd/for_each.h

@@ -0,0 +1,28 @@
+#ifndef RCPP_PARALLEL_SIMD_FOR_EACH_H
+#define RCPP_PARALLEL_SIMD_FOR_EACH_H
+
+namespace boost {
+namespace simd {
+
+template <typename T, typename F>
+void for_each(const T* it, const T* end, F& f)
+{
+   typedef boost::simd::pack<T> vT;
+   static const std::size_t N = vT::static_size;
+   const T* aligned_begin = std::min(boost::simd::align_on(it, N * sizeof(T)), end);
+   const T* aligned_end   = aligned_begin + (end - aligned_begin) / N * N;
+   
+   for (; it != aligned_begin; ++it)
+      f(*it);
+   
+   for (; it != aligned_end; it += N)
+      f(boost::simd::aligned_load<vT>(it));
+   
+   for (; it != end; ++it)
+      f(*it);
+}
+
+} // namespace simd
+} // namespace boost
+
+#endif /* RCPP_PARALLEL_SIMD_FOR_EACH_H */