How can I get Inline::C to deal with big number?

Hi,

I have the following code that uses Inline::C to compute factorial.
The problem is that whenever I use large N (>30) it began to return "INF".

I thougtht my C implementation already cater large number by using "float"?
Additionally I have already added Math::Pari as an attempt to solve
the problem, but again no avail.

Can anybody suggest what's the way to deal with this?

Here is my complete code:


#----------Beginning of my code ---------------

#!/usr/bin/perl -w
use Inline C;
use strict;
use Data::Dumper;
use Math::Pari qw/ :int/;

my $n = factrl(30);  # it fails if I try factrl(40)
print "$n\n"


__END__
__C__

#include <stdio.h>


float factrl(int n)
{
float gammln(float xx);
void nerror(char error_text[]);
static int ntop=4;
static float 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];

}

float gammln(float 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);
}


#-----End of My Code--------------


--
Edward WIJAYA
Singapore

On Sat, 26 Mar 2005 12:22:18 +0800, ewijaya@singnet.com.sg (Edward
Wijaya) wrote:

>Hi,
>
>I have the following code that uses Inline::C to compute factorial.
>The problem is that whenever I use large N (>30) it began to return "INF".
>
>I thougtht my C implementation already cater large number by using "float"?
>Additionally I have already added Math::Pari as an attempt to solve
>the problem, but again no avail.
>
>Can anybody suggest what's the way to deal with this?
>
>Here is my complete code:

Change every occurence of the word "float" , in your script,
to "double".




--
I'm not really a human, but I play one on earth.
http://zentara.net/japh.html

Hi Zentara,
Thanks for the reply.

On Sat, 26 Mar 2005 21:35:17 +0800, zentara <zentara@highstream.net> wrote:


> Change every occurence of the word "float" , in your script,
> to "double".

It worked, but still limited. It overflowed when N>500.
Most of the value of N, I use are around 1000-2000.

Any other possibility?


--
Edward WIJAYA
Singapore

On 26 Mar, Edward Wijaya wrote:
 
>
> It worked, but still limited. It overflowed when N>500.
> Most of the value of N, I use are around 1000-2000.
>
> Any other possibility?

Try "long double" instead, which gives you 10 Bytes and
the format char %Lf.

Hi Steven,

On Sat, 26 Mar 2005 22:08:44 +0800, Steven Schubiger
<steven@accognoscere.org> wrote:

> Try "long double" instead, which gives you 10 Bytes and
> the format char %Lf.
>

Still wont' do. It still return 'inf' for N>500


--
Edward WIJAYA
Singapore

On 26 Mar, Edward Wijaya wrote:
 

> Still wont' do. It still return 'inf' for N>500

What does printf("%i\n", sizeof(long double)); tell you?
The byte sizes of variable types can vary from platform to platform.

> On 26 Mar, Edward Wijaya wrote:
 

> Still wont' do. It still return 'inf' for N>500

Another solution would be, dynamically allocating memory:

long double var;
var = (long double *) malloc(2*sizeof(long double));

On 26 Mar, Edward Wijaya wrote:
 
>
> It gives:
> 12

Fine, it was even 2 Bytes bigger than excepted.

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

var should measure 24 bytes in size, which should suffice;
if not, increment the factor accordingly.

On Sat, 26 Mar 2005 22:31:52 +0800, Steven Schubiger
<steven@accognoscere.org> wrote:


> typedef (malloc(2*sizeof(long double))) Big_Double;
> Big_Double var;
>

Sorry my C is barely Novice.
Where can I put this snippet in my C subroutine?

like this:
[snip code]

__END__
__C__


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

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);
}


--
Edward WIJAYA
Singapore

On 26 Mar, Edward Wijaya wrote:

> Sorry my C is barely Novice.
> Where can I put this snippet in my C subroutine?

It's fine, as it is. Typedefs most often reside in header files,
although, they can be used in the main file without suffer.

If you ever should get bored, read the Perl Sources.