Hi,
Here is the code that tries to compute factorial based on Numerical Recipes using Inline::C.

My question is, how can I improve my code below so that it can handle large number? Does Inline::C support malloc for typdef?

I've tried "Math::Pari qw(:int)" but of no avail. So I thought malloc should be the better way to go. 
#!/usr/bin/perl -w
use strict;
use Inline qw(C);
use Data::Dumper;

my $n = factrl(1000); 
print "$n\n";


__END__

 __C__

/* Here I attempt to increase the size of variable 
   with malloc such that it can handle BIG number 
   But is there anything wrong with it? */

typedef (malloc(2*sizeof(long double))) Big_Double;
Big_Double factrl;

/* Code below is to compute factorial */

double factrl(int n)
{
  double gammln(double xx);
  void nerror(char error_text[]);
  static int ntop=4;
  static double a[33]={1.0,1.0,2.0,6.0,24.0};
  int j;

  if (n<0) nerror("Negative factorial in routine factrl");
  if (n>32) return exp(gammln(n+1.0));
  
  while (ntop<n){
    j = ntop++;
    a[ntop]=a[j]*ntop;
  }
  
  return a[n];

}

double gammln(double xx)
{
  double x,y, tmp,ser;
  static double cof[6] = {76.18009172947146, -86.50532032941677,
                          24.01409824083091, -1.231739572450155,
                          0.12086509738661e-2, -0.5395239384953e-5};
  int j;

  y = x = xx;
  tmp= x+5.5;
  tmp -= (x+0.5)*log(tmp);
  ser=1.000000000190015;
  
  for (j=0;j<=5;j++) ser += cof[j]/++y;
  return -tmp+log(2.5066282746310005*ser/x);
}

[download]
Regards,
Edward

Update: I've also tried "use Math::GMP qw(:constant);" also can't handle big N.

In reply to Malloc with Inline::C by monkfan

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