Segfault games with factorials

[John Colvin via Digitalmars-d-learn]

On Thursday, 24 July 2014 at 14:59:16 UTC, Darren wrote:
> On Thursday, 24 July 2014 at 14:39:12 UTC, H. S. Teoh via 
> Digitalmars-d-learn wrote:
>> On Thu, Jul 24, 2014 at 01:14:40PM +0000, Darren via 
>> Digitalmars-d-learn wrote:
>>> I have the following code in fac.d (modified from the 
>>> factorial
>>> examples on RosettaCode):
>>> 
>>> #!/usr/bin/rdmd
>>> import std.bigint;
>>> 
>>> pure BigInt factorial(BigInt n) {
>>>    static pure BigInt inner(BigInt n, BigInt acc) {
>>>    	return n == 0 ? acc : inner(n - 1, acc * n);
>>>    }
>>>    return inner(n, BigInt("1"));
>>> }
>>> 
>>> void main(string[] args) {
>>> 	import std.stdio;
>>> 	BigInt input = args[1];
>>> 	writeln(factorial(input));
>>> 	return;
>>> }
>>> 
>>> It (more or less consistently) on my machine will calculate 
>>> 'fac
>>> 47610', and (more or less consistently) will core dump with a 
>>> segfault
>>> on 'fac 47611'.
>> [...]
>>
>> You're probably running out of stack space because of your 
>> recursive
>> function. Write it as a loop instead, and you should be able 
>> to go
>> farther:
>>
>> 	pure BigInt factorial(BigInt n) {
>> 		auto result = BigInt(1);
>> 		while (n > 1)
>> 			result *= n;
>> 		return result;
>> 	}
>>
>>
>> T
>
> It does seem that's the case. Which is odd, as I thought that 
> DMD and LDC did TCO. Not in this case obviously.
>
> PS. This was a slightly silly program, but in the general case, 
> is there a way to use a core dump to diagnose a stack overflow?

A debugger should be able to tell you why the segfault occurred.