Re: imag () function detail regarding -0.0000

[Daniel J Sebald]

On 09/12/2012 04:21 PM, Dmitri A. Sergatskov wrote:
> Daniel J Sebald<address@hidden>  wrote:
>
> > So, Octave appears to be fairly adherent to the IEEE 754 standard.  I can
> > get used to having the -0 floating about, but it is kind of annoying in
> > arithmetic operations seeing this as I really only think of +/-0 related to
> > convergence.
>
> I do not believe Octave does anything special wrt IEEE 754 beyond what
> underlying C++ compiler/library does.
> That came up few times and the conclusion was that it is not Octave's business
> to fix compiler bugs/missing features.

I see that's the case.  I just tried some things with a minimal main(){} 
program.


> GCC compliance with IEEE 754 is iffy at the moment. The result may even change
> with different optimization level.

The gcc man page says that isn't affected by optimization level, i.e., 
-O1, -O2, etc.  There are optimization flags that affect this however, 
and some that ensure full compliance.  For example, there is

-fno-signed-zeros

which means that the compiled code will produce no signed zeros.  The 
compiler will then optimize out a few small things that it generally 
shouldn't.  (That's not something for a program like Octave.)  Can't 
really change fprintf() easily either, as that is inside a library.

The elegant solution (three zeros) doesn't fall under gcc or Octave.

Dan