factorial problems

[kaasknak]

I am currently busy on a script that is supposed to be used for calculating the factorials of given numbers this is the current script.

$faculteit = faculteit(26)
msgbox (0, "", $faculteit)

Func faculteit($nummer)
Local $n = 1

For $i = 1 to $nummer
$n = $n*$i
Next

If $n = 0 Then
SetError ( 1 )
Return 1
Else
Return $n
EndIf
EndFunc

The problem is this works fine until it goes up to 26! then the numbers start going all wrong.

Anybody know what's causing this problem?

Thanks for your time

[Melba23]

kaasknak,

At a guess you have reached the upper limit for integers.

There is a BigNum UDF somewhere on the forum which might be helpful.

M23

[trancexx]

You can also do:

Local $n = 1.0

... and then do calculation.

[kaasknak]

The last option worked.

Thanks

[jchd]

What is the upper bound of the integers you're going to need factorial?

Which accuracy do your application need?

[Mat]

Are you sure you get to 26! without problems? Log_2(26!) is 89, which is far larger than the largest AutoIt integers. The highest you should be able to do is 20!.

[jchd]

Indeed!

In[1]:={20!, 2⁶³ - 1, 2⁶⁴ - 1, 26!}

Out[1]={

2432902008176640000 ; 20!

9223372036854775807 ; max signed int64

18446744073709551615 ; max unsigned int64

403291461126605635584000000 ; 26!

}