Re: signbit and logical tests

[Michael D. Godfrey]

On 02/10/2013 11:05 AM, Mike Miller wrote:
> On Sun, Feb 10, 2013 at 1:37 AM, Michael D. Godfrey wrote:
> > >It is curious.  The code (in libinterp/corefcn/mappers.cc) seems to
> > >read as it will return an integer which is what the C++ signbit function
> > >does.
> > >However:
> > >octave:1> sbit = signbit(-1.2)
> > >sbit =  1
> > >octave:2> whos
> > >Variables in the current scope:
> > >
> > >    Attr Name        Size                     Bytes  Class
> > >    ==== ====        ====                     =====  =====
> > >         sbit        1x1                          8  double
> > >
> > >So, I am missing something.
> The function called there is xsignbit, which is defined at
>
> http://hg.savannah.gnu.org/hgweb/octave/file/999f8257313b/liboctave/numeric/lo-mappers.h#l404
>
> This template function returns the same type as the argument.
>
> -- mike
But, John said:
> The signbit function in Octave is just a simple wrapper around the 
> system library signbit function, and that returns the value of the 
> sign bit as an integer.  I don't know whether it would be a good idea 
> to change that definition for Octave.  The other function that I know 
> of in Matlab that returns something different from what the C library 
> function returns is strcmp.  So there is precedent for that kind of 
> thing.  Or, if you want a predicate-style function, maybe we should 
> have isnegative instead?
>
> jwe
I think that return logical would be more consistent with other Octave 
"logical" functions.
Changing signbit to isnegative is possible, but, of course, sort order 
treats -0 as 0, so isnegative
would be a bit confusing.

Michael