C vs Rcpp for monte carlo pi approximation
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Rcpp_code <- " | |
#include <Rcpp.h> | |
// [[Rcpp::export]] | |
double mcsim_rcpp(const int n){ | |
int i, r = 0; | |
double u, v; | |
Rcpp::RNGScope scope; | |
for (i=0; i<n; i++){ | |
u = R::runif(0, 1); | |
v = R::runif(0, 1); | |
if (u*u + v*v <= 1) | |
r++; | |
} | |
return (double) 4.*r/n; | |
} | |
" | |
C_code <- " | |
#include <R.h> | |
#include <Rinternals.h> | |
// [[Rcpp::export]] | |
SEXP mcsim_c(SEXP n_){ | |
SEXP ret; | |
int i, r = 0; | |
const int n = INTEGER(n_)[0]; | |
double u, v; | |
GetRNGstate(); | |
for (i=0; i<n; i++){ | |
u = unif_rand(); | |
v = unif_rand(); | |
if (u*u + v*v <= 1) | |
r++; | |
} | |
PutRNGstate(); | |
PROTECT(ret = allocVector(REALSXP, 1)); | |
REAL(ret)[0] = (double) 4.*r/n; | |
UNPROTECT(1); | |
return ret; | |
} | |
" | |
library(Rcpp) | |
sourceCpp(code=Rcpp_code) | |
sourceCpp(code=C_code) | |
mcsim_c(100L) | |
mcsim_rcpp(100L) | |
mcsim_rcpp(100) | |
mcsim_c(100) ### uh-oh |
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