R devel - Dec 2000 - nmath bug (PR#762)

Hi,
	I've been playing with the standalone math library (R.1.1.1,
Redhat 7 i386), and have detected a problem with rpois.


Basically, the rejection step in rpois can result in an infinite loop.
The simplest thing I can come up with that reproduces the problem is
the following.


#include <stdio.h>
#include <math.h>
#include <time.h>

#define MATHLIB_STANDALONE
#include "Mathlib.h"

int main() {
  double d;

  set_seed(976259805U,2968367341U);

  for(long k=0; k<10; k++) {
    for(long k=0; k<10000; k++) d = rpois(4500);
    for(long k=0; k<250000; k++) d = rpois(100);
    printf(".");
    fflush(stdout);
  }
}

Fro me this prints 3 dots and then hangs.

I realize calling rpois with means this large is probably not the
wisest thing to do, nevertheless, I still consider the infinite loop
to be a bug, hence this report.

Sorry that I cannot give a simpler example than this, its taken me
quite a while to get this far, and as my debugging efforts were going
nowhere, I thought it better to throw it out to the wider community.

Simon




-- 
*****************************************************************
*  Simon Wotherspoon                               _--_|\       *
*  Maths Dept, University of Tasmania             /  Aus \      *
*  Tasmania, Australia                            \_.--._/      *
*  spoon@hilbert.maths.utas.edu.au                      v       *
*****************************************************************


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spoon@hilbert.maths.utas.edu.au writes:
> Hi,
> 	I've been playing with the standalone math library (R.1.1.1,
> Redhat 7 i386), and have detected a problem with rpois.
> 
> 
> Basically, the rejection step in rpois can result in an infinite loop.
> The simplest thing I can come up with that reproduces the problem is
> the following.
Hmm. There are bugs in rpois from 1.1.1 *and* compiler bugs in redhat7
that are known to affect rpois...

In order to get something that has a decent chance of working you
should probably use a *very* recent gcc from the rawhide distribution,
and try a snapshot of 1.2.0. 

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