[Haskell-cafe] In-place modification

[Jon Harrop]

On Sunday 15 July 2007 11:19:29 Hugh Perkins wrote:
> Not only does mono come close to the Microsoft .Net time, both mono and
> Microsoft .Net are faster than g++ ;-) and whack Haskell.

This should tell you that your C++ is not very good. This is several times 
faster, for example:

#include <iostream>
#include <ctime>
#include <vector>

using namespace std;

int CalculateNumberOfPrimes(int maxprime)
{
  vector<bool> NotPrime(maxprime+1);
  
  int NumberOfPrimes = 0;
  
  for (int i = 2; i <= maxprime; i++ )
    if (!NotPrime[i])
      {
	++NumberOfPrimes;
	for (int j = 2*i; j <= maxprime; j += i)
	  if (!NotPrime[j]) NotPrime[j] = true;
      }
  
  return NumberOfPrimes;
}

For some reason you were using C-style allocation rather than the C++ STL to 
implement a bit vector. The STL implementation is optimized.

-- 
Dr Jon D Harrop, Flying Frog Consultancy Ltd.
The OCaml Journal
http://www.ffconsultancy.com/products/ocaml_journal/?e