Segfault games with factorials
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'.
Interestingly, if I redirect stdout to a file it will usually
manage to get to 47612.
To satisfy my own curiosity about what's happening, are there any
resources I can use to analyse the core dump?
Thanks.
Re: Segfault games with factorials
On Thu, Jul 24, 2014 at 01:14:40PM +, 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
--
Ignorance is bliss... until you suffer the consequences!
Re: Segfault games with factorials
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 +, 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?
Re: Segfault games with factorials
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 +, 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.
Re: Segfault games with factorials
On Thursday, 24 July 2014 at 14:59:16 UTC, Darren wrote: It does seem that's the case. Which is odd, as I thought that DMD and LDC did TCO. Not in this case obviously. DMD doesn't do it with the :? operator: https://issues.dlang.org/show_bug.cgi?id=3713
