[Bug middle-end/19974] incorrect complex division on ia-64 with flag_complex_method = 2

Thomas dot Koenig at online dot de gcc-bugzilla@gcc.gnu.org
Wed Feb 16 17:27:00 GMT 2005

------- Additional Comments From Thomas dot Koenig at online dot de  2005-02-16 12:41 -------
I think I have identified the problem.

The hang itself is probably caused by a Lapack bug, because slarrb is
only fed 0. and NaN as arguments.

The reason why this is so is probably due to a problem in complex
division with flag_complex_method = 2.  Here's a test case:

$ cat c-tst.c
#include <stdio.h>
#include <math.h>
#include <complex.h>

int main()
    float complex a,b,c;
    a = 1.e20-I*1.e12;
    b = 1. - I*1.e-8;
    c = a/b;
    printf("%.5g %.5g\n",creal(c),cimag(c));
    return 0;

This has flag_complex_medhod = 2:

$ gcc -B ~/gcc-C2/gcc c-tst.c
$ ./a.out
1e+20 18059

This has flag_complex_method = 1:

$ gcc -B ~/gcc-C1/gcc c-tst.c
$ ./a.out
1e+20 0

Probably a wrong sign when recovering from overflow in the
new complex division routines.

Adding rth to the cc list.

           What    |Removed                     |Added
                 CC|                            |rth at gcc dot gnu dot org
OtherBugsDependingO|                            |18902
              nThis|                            |
            Summary|Lapack hang in xeigtstc on  |incorrect complex division
                   |ia-64                       |on ia-64 with
                   |                            |flag_complex_method = 2


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