[Haskell-cafe] In-place modification

[Hugh Perkins]

Hey, I just realized I can shave off another 30% in C# ;-)

So now the timings become:

Safe Haskell
=========

J:\dev\haskell>ghc -O2 -o primechaddai.exe PrimeChaddai.hs

J:\dev\haskell>primechaddai
number of primes: 664579
Elapsed time: 26.234

Unsafe Haskell
===========

J:\dev\haskell>ghc -fglasgow-exts -O2 -o PrimeDonald2.exe PrimeDonald2.hs

J:\dev\haskell>primedonald2
number of primes: 664579
Elapsed time: 0.7030000000000001

mono
====

J:\dev\test\testperf>erase primecs.exe & gmcs primecs.cs

J:\dev\test\testperf>mono primecs.exe
number of primes: 664579
elapsed time: 0,453

Microsoft.Net
==========

J:\dev\test\testperf>erase primecs.exe & csc /nologo primecs.cs

J:\dev\test\testperf>primecs
number of primes: 664579
elapsed time: 0,421875

Here's the fabulously complicated ;-) new C# algorithm:

    public int  CalculateNumberOfPrimes( int maxprime )
    {
    bool[]IsNotPrime = new bool[ maxprime ];
        int NumberOfPrimes = 1;

        int squarecutoff = (Int32)Math.Sqrt( maxprime ) + 1;
        for( int i = 3; i < maxprime; i+= 2 )
        {
            if( !IsNotPrime [i] )
            {
                NumberOfPrimes++;
                if( i < squarecutoff )
                {
                for( int j = ( i << 1 ); j < maxprime; j+= i )
                {
            if( !IsNotPrime [j] )
                        IsNotPrime [ j] = true;
                }
                }

            }
        }
        return NumberOfPrimes;
    }

(basically, we only cross off primes up to the square root of the size of
the grid.  I think this is a standard part of the standard Arostophenes grid
algorithm, so like I say the C# version is seriously unoptimized ;-) )
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