On 7/9/2018 3:07 PM, Corinna Vinschen wrote: > 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. >
I don't see a fetestexcept() being used. Setting all the bits is definitely going to raise an exception. >>> 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. Yes, see: https://en.cppreference.com/w/c/numeric/fenv/FE_exceptions -- cyg Simple -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple