🚀 go-pugleaf

Randal L. Schwartz (merlyn@stonehenge.com) wrote:
: >>>>> "Tim" == Tim Hollebeek <tim@franck> writes:

: Tim> An important point, though, is that all 'reasonably' written C programs
: Tim> will run within a factor of 2 or so of 'about as fast as you can get,
: Tim> while for some problems, Perl won't be able to break through about a
: Tim> factor of 7 or so, even if you are a Perl expert.

: I just want to point out to everyone that you are simply making that
: figure up based on what you think Perl is doing internally.

: Tom Christiansen has had a long-standing bet that someone can't give
: him a program in C that he can't make run no more than "e" times
: slower (about 2.8 for you non-math-geeks) in Perl.  So far, no one's
: done it.

	I find that exceptionally hard to beleive.  What is this bet 
exactly?  Do I get any money for "winning" it?  For example, I have 
some programs that are heavily math-intensive, ( matrix multiplies,
number cracking, image manipulation ) which I have written in C, 
which I would be shocked as all get-out to see run nearly as fast in 
PERL.

: That's also been my experience as well.  Perl is *not* slow.  In fact,
: a Perl-written egrep is *faster* than most vendor's egrep, for
: example.

	Sure, as long as you are writing grep, it's great.  That's
because you're then spending 99% of your time in some C code that's
already been way optimized.

: So, if you have a number of "7-times-slower" programs, post'em, and I
: bet we can easily boost their speed by two or three times.

	Okay.  It's a bit long, but this finds amicable number pairs
using the dumb old-try-every-number method.  I'd be shocked to see a
2.8 factor, and be even mildly surprised to even see 7 times as fast
C->Perl.

#include <iostream.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

typedef unsigned int Int;
char *Table;

unsigned int SumOfFactors( Int Num )
{
    Int Res = 1;
    Int SNum = Int( floor( sqrt( (double) Num ) ) );
    memset( Table , 0 , SNum );
    for( Int i = 2 ; i < SNum ; ++ i )
    {
      if ( Table[ i ] == 0 )
      {
        int divresult = Num / i;
        int Remainder = Num - ( divresult * i ) ;
        if ( Remainder == 0 )
	{
	  Res += i;
	  Res += divresult;
	}
        else
        {
          int temp = i;
          while( temp < SNum )
          {
            Table[ temp ] = 1;
            temp += i;
          }
        }
      }
    }
    return Res;
}

main( int argc , char *argv[] )
{
    Table = new char[ 1000000 ];

    for( Int i = 1 ; i < 1000000000 ; ++i )
    {
        if ( ( i % 100000 ) == 0 )
        {
            cout << "Reached " << i << endl;
        }
        Int r1 = SumOfFactors( i );
        if ( r1 == i )
            cout << "Perfect " << i << endl;
        else
        {
            Int r2 = SumOfFactors( r1 );
            if ( r2 == i )
                cout << "Amicable : " << r1 << " " << r2 << endl;
        }
    }
}
        


--
------------------------------------------------------------------------------
David Hanley,                 |______     Computer Science graduate student.  
dhanley@lac.ecs.uic.edu       |\ ___/__  Martial Artist. Biker. Chess Freak   
www_lac.eecs.uic.edu/~dhanley/| \\ /  / Libertarian.  Atheist.  Bisexual.     
My employer barely KNOWS me.  |  \/BI/ Aspiring novelist.Joyce Kafka Neitzchie
-----------------------------------\/-----------------------------------------
Member:Hermetic order of the Golden Dawn.