ConvolveBenchmarks/convolve4_cpp.cpp

An even more efficient version of the basic convolution example from Section 5.10.1 of 'Writing R Extensions', now rewritten for Rcpp and using Rcpp::NumericVector as well as direct pointer operations for better performance.

// -*- mode: C++; c-indent-level: 4; c-basic-offset: 4; tab-width: 8 -*-

// This is a rewrite of the 'Writing R Extensions' section 5.10.1 example

#include <Rcpp.h>

RcppExport SEXP convolve4cpp(SEXP a, SEXP b) {
    Rcpp::NumericVector xa(a);
    Rcpp::NumericVector xb(b);
    int n_xa = xa.size() ;
    int n_xb = xb.size() ;
    int nab = n_xa + n_xb - 1;
    Rcpp::NumericVector xab(nab,0.0);
    
    double* pa = xa.begin() ;
    double* pb = xb.begin() ;
    double* pab = xab.begin() ;
    int i,j=0; 
    for (i = 0; i < n_xa; i++)
        for (j = 0; j < n_xb; j++) 
            pab[i + j] += pa[i] * pb[j];

    return xab ;
}

#include "loopmacro.h"
LOOPMACRO_CPP(convolve4cpp)