http://www.perlmonks.org?node_id=442521

monkfan has asked for the wisdom of the Perl Monks concerning the following question:

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); }
Regards,
Edward

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