Thread

Trouble with exp() on S/Linux?

Keith Parks <emkxp01@mtcc.demon.co.uk> — 1998-01-09T15:53:57Z

Hi,

I have built and installed the latest version of the PostgreSQL RDBMS
on S/Linux but am having problems with the regression tests.

Many of the failures come from floating point exceptions.

I've written a small c prog to demonstrate the problem which seems to
show that using exp() on a number less than 1.0e-150 gives an FPE.

Can anyone tell me what's broken, if anything.

I'm really not sure whether it is...

cpu    : Fujitsu or Weitek Power-UP
fpu    : Fujitsu or Weitek on-chip FPU               
kernel : sparclinux-2.0-980106
libc/m : libc.so.5.3.12/libm.so.5.0.6
gcc    : gcc version 2.7.2.1

Something else???
Expected behaviour???

The machine is a SPARCstation IPX running Red Hat 4.2.

Thanks for any help,
Keith.

[emkxp01@sparclinux ~]$ cat mxdb.c
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <float.h>

main()
{
        double dbval;

        dbval = atof("1.0e-150");
        printf("dbl1 = %e\n", dbval);
        printf("Exp dbl1 = %e\n", exp(dbval));
        dbval = atof("1.0e-151");
        printf("dbl2 = %e\n", dbval);
        printf("Exp dbl2 = %e\n", exp(dbval));
}                                            
[emkxp01@sparclinux ~]$ gcc mxdb.c -lm
[emkxp01@sparclinux ~]$ ./a.out
dbl1 = 1.000000e-150
Exp dbl1 = 1.000000e+00
dbl2 = 1.000000e-151
Floating exception (core dumped)