[Pkg-octave-devel] Re: Sparse + complex arithmetic inconsistency

[John W. Eaton]

On 30-Mar-2007, David Bateman wrote:

| Or a slightly modification
| 
| #include <math.h>
| #include <complex.h>
| #include <stdio.h>
| int main(int argc, char *argv[])
| {
|   complex double b=1,c=I*1,d = 1+I*1,z = 0.;
|   // This should produce (inf,0), not (nan,nan).
|   printf("(%f,%f) / (%f,%f) -> (%f,%f)\n",
|          creal(b),cimag(b),creal(z),cimag(z),creal(b/z),cimag(b/z));
|   // This should produce (0,inf), not (nan,nan).
|   printf("(%f,%f) / (%f,%f) -> (%f,%f)\n",
|          creal(c),cimag(c),creal(z),cimag(z),creal(c/z),cimag(c/z));
|   // This should produce (inf,inf), not (nan,nan).
|   printf("(%f,%f) / (%f,%f) -> (%f,%f)\n",
|          creal(d),cimag(d),creal(z),cimag(z),creal(d/z),cimag(d/z));
|   return 0;
| }
| 
| that all return (nan,nan) for me.

Here is what I see:

$ gcc foo.c
$ ./a.out
(1.000000,0.000000) / (0.000000,0.000000) -> (nan,nan)
(0.000000,1.000000) / (0.000000,0.000000) -> (nan,nan)
(1.000000,1.000000) / (0.000000,0.000000) -> (nan,nan)
$ gcc -O2 foo.c
$ ./a.out
(1.000000,0.000000) / (0.000000,0.000000) -> (inf,0.000000)
(0.000000,1.000000) / (0.000000,0.000000) -> (0.000000,inf)
(1.000000,1.000000) / (0.000000,0.000000) -> (inf,inf)
$ gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --with-tune=i686 --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)

Is that acceptable behavior or a bug?

I seem to recall this problem coming up before, and we may have even
discussed it on the bug or maintainers list (the topic just seems
familiar; I haven't tried to find the thread in the archives).

jwe