Justin,
> > What man page is this intended for?
> qsort()
>
> > > Included is a sample program that demonstrates how to sort IEEE
> > > floating point values, including NAN and friends, in a useful way;
> > > please consider including it.
> > >
> > > // make CFLAGS='-W -Wall -O3 -g -std=gnu99' LDFLAGS=-lm fpnansort
> > > #include <math.h>
> > > #include <stdlib.h>
> > > #include <stdio.h>
> > > #include <assert.h>
> > >
> > > int fpcomp(const void *a, const void *b)
> > > {
> > > double x=*(double *)a,
> > > y=*(double *)b;
> > >
> > > if (x<y) return -1;
> > > else if (x>y) return 1;
> > > // The not-normal values will be grouped together, but
> > > // otherwise unordered:
> > > else if (!isnormal(x)) return 1;
> > > else if (!isnormal(y)) return -1;
> >
> > Why isnormal()?
> "Why not" ?
>
> Seriously, I want all the IEEE special number foo to get out of my
> way, and this does wha tI want.
Do you realise that "!isnormal(0.0) == 1"?
What happens when you compare 0.0 with 0.0?
> > > assert(x==y);
> >
> > What is assert doing here?
> Well, the current qsort() example uses assert() on argc, so why not?
The context is different: one kills the program because it
got bad arguments. The other kills the quicksort because
the comparison function encountered a case that it didn't expect.
It just looks a bit strange is all.
> Seriously, I *think* that x==y is guaranteed, since x and y are both
> "normal" values, but there might be other special cases of which I'm
> not even aware; this is as way of checking for them, and at the same
> time indicating my intent. (Actually, "subnormal" may just be that
> case .. will think about it.)
I'm *not at all* convinced that including an example like this is
appropriate for the qsort man page: it isn't the place to teach
about floating point numbers.
Cheers,
Michael
--
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7
Want to help with man page maintenance?
Grab the latest tarball at
ftp://ftp.win.tue.nl/pub/linux-local/manpages/,
read the HOWTOHELP file and grep the source
files for 'FIXME'.
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