On Jul 9 11:16, Brian Inglis wrote:
> On 2018-07-09 10:49, Corinna Vinschen wrote:
> > On Jul 9 15:47, Lavrentiev, Anton (NIH/NLM/NCBI) [C] wrote:
> >> Hello,
> >>
> >> the following sample coredumps with FPE at localhost.cc:1962 with the
> >> latest snapshot (6/29/2018):
> ...
> > You can simplify your testcase by not calling any time functions:
> >
> > #define _GNU_SOURCE
> > #include <fenv.h>
> > #include <stdio.h>
> > #include <stdlib.h>
> >
> > #define SECSPERDAY 86400
> >
> > int main(int argc, char **argv)
> > {
> > feenableexcept(FE_ALL_EXCEPT);
> > long tdays = argc > 1 ? strtol (argv[1], NULL, 10) : 189;
> > long seconds = tdays * SECSPERDAY + 0.5;
> > printf ("%ld\n", seconds);
> > }
> >
> > This generates a SIGFPE on Linux as well.
> >
> > The line computing seconds is the same line as used by the localtime
> > function. Cygwin shares the entire localtime code with the various
> > BSDs, so I guess they would have the same problem.
> What is that line meant to do? Am I missing something?
> It should be the equivalent of (tdays*SECSPERDAY*2 + 1)/2!
> It converts an integer value to double, adds 1/2, and throws it away on
> conversion back, unless the intermediate has insufficient mantissa bits, in
> which case, it loses the low bits?You may want to ask the original author why he used FP arithmetic in this place. Maybe it's a way to avoid integer overflow. I'm reluctant to change this given that this code is still used in BSD as well. > > Bottom line is, don't bulk enable FP exceptions, but only if you really > > need it for certain parts of your code. Don't expect library functions > > to be SIGFPE clean under all circumstances. > > Maybe selectively enable specific FPEs to check for where needed. > Or be careful what you wish for, as you just might get a lot more than you > bargained for ;^> That's what I meant. Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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