On 7/14/07, Henk-Jan van Tuyl <[EMAIL PROTECTED]> wrote:
There was some discussion about prime number generators earlier this year:
http://www.haskell.org/pipermail/haskell-cafe/2007-February/022347.html
http://www.haskell.org/pipermail/haskell-cafe/2007-February/022699.html
Ok, so using the following code:
module Main
where
import IO
import Char
import GHC.Float
import List
import Control.Monad
import System.Time
import System.Locale
sieve :: [Int] -> [Int]
sieve [] = []
sieve (p : xs) = p : sieve [x | x <- xs, x `mod` p > 0]
calculateNumberOfPrimes :: Int -> Int
calculateNumberOfPrimes max = 1 + length( sieve [ 3,5.. (max -1) ] )
gettime :: IO ClockTime
gettime = getClockTime
main = do starttime <- gettime
let numberOfPrimes = (calculateNumberOfPrimes 200000)
putStrLn( "number of primes: " ++ show( numberOfPrimes ) )
endtime <- gettime
let timediff = diffClockTimes endtime starttime
let secondsfloat = realToFrac( tdSec timediff ) +
realToFrac(tdPicosec timediff) / 1000000000000
putStrLn( show(secondsfloat) )
return ()
With "200000" as the upper limit on the sieve, this gives:
O:\dev\haskell>ghc -fglasgow-exts -O2 -o prime.exe Prime.hs
O:\dev\haskell>prime
number of primes: 17984
8.734
For comparison, on the same machine, in C# this gives:
O:\dev\test\testperf>csc /nologo primecs.cs
O:\dev\test\testperf>primecs
number of primes: 17984
elapsed time: 0,015625
That's over 500 times faster ;-)
Here's the code in C#
using System;
class Primes
{
public int CalculateNumberOfPrimes( int maxprime )
{
bool[]IsNotPrime = new bool[ maxprime ];
int NumberOfPrimes = 1;
for( int i = 3; i < maxprime; i+= 2 )
{
if( !IsNotPrime [i] )
{
NumberOfPrimes++;
for( int j = ( i << 1 ); j < maxprime; j+= i )
{
if( !IsNotPrime [j] )
IsNotPrime [ j] = true;
}
}
}
return NumberOfPrimes;
}
}
class EntryPoint
{
public static void Main()
{
System.DateTime start = System.DateTime.Now;
int NumberOfPrimes = new Primes().CalculateNumberOfPrimes( 200000 );
System.DateTime finish = System.DateTime.Now;
double time = finish.Subtract( start ).TotalMilliseconds;;
Console.WriteLine( "number of primes: " + NumberOfPrimes );
Console.WriteLine( "elapsed time: " + ( time / 1000 ) );
}
}
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