## vendredi 27 juin 2014

### Ocaml Optimization Techniques

I am new to Ocaml (with some prior knowledge in Haskell). And I want to persuade myself to adopt Ocaml. Therefore I tried to compare the performance between C and Ocaml. I wrote the following naïve Monte Carlo Pi-finder:

## C Version

``#include <stdio.h>#include <stdlib.h>int main(int argc, const char * argv[]) {    const int N = 10000000;    const int M = 10000000;    int count = 0;    for (int i = 0; i < N; i++) {        double x = (double)(random() % (2 * M + 1) - M) / (double)(M);        double y = (double)(random() % (2 * M + 1) - M) / (double)(M);        if (x * x + y * y <= 1) {            count++;        }    }    double pi_approx = 4.0 * (double)(count) / (double)(N);    printf("pi .= %f", pi_approx);    return 0;}``

## Ocaml Version

``let findPi m n =     let rec countPi count = function         | 0 -> count        | n ->            let x = float_of_int (Random.int (2 * m + 1) - m) /. (float_of_int m) in            let y = float_of_int (Random.int (2 * m + 1) - m) /. (float_of_int m) in            if x *. x +. y *. y <= 1. then                countPi (count + 1) (n - 1)            else                countPi count (n - 1) in    4.0 *. (float_of_int (countPi 0 n)) /. (float_of_int n);;let n = 10000000 inlet m = 10000000 inlet pi_approx = findPi m n inPrintf.printf "pi .= %f" pi_approx``

I compiled the C with Clang (Apple LLVM version 5.1) and the Ocaml with OCamlopt v4.01.0.

The running time of C is 0.105s. The Ocaml one is 0.945s, which is 9 times slower. My target is to reduce the running time of Ocaml by 3 times, so that the program can finish within 0.315s.

As I am so new to Ocaml, I want to learn some Ocaml optimization techniques. Please leave me some suggestions! (Tail-resursion is already applied)