Previously POSIX::signbit() had a fallback implementation for the case Perl_signbit is not defined, but this code is apparently broken because it returns wrongly non-zero (true) value for signbit(+0.0).
Currently Perl_signbit is always defined (either as a macro or as a function), so it seems to be better to use it unconditionally.

Additionally, unused macro c99_signbit is deleted, which is also apparently broken because there is no signbitl() in C99.

Can you specify more precisely what you mean by previously and currently?

Previously POSIX::signbit() had a fallback implementation for the case Perl_signbit is not defined, but this code is apparently broken because it returns wrongly non-zero (true) value for signbit(+0.0).
Currently Perl_signbit is always defined (either as a macro or as a function), so it seems to be better to use it unconditionally.

Additionally, unused macro c99_signbit is deleted, which is also apparently broken because there is no signbitl() in C99.

@khwilliamson, @doughera88 You have worked on what appears to be a relevant section of numeric.c. Could you take a look at this p.r.?

Thank you very much.
Jim Keenan

Previously POSIX::signbit() had a fallback implementation for the case Perl_signbit is not defined, but this code is apparently broken because it returns wrongly non-zero (true) value for signbit(+0.0).
Currently Perl_signbit is always defined (either as a macro or as a function), so it seems to be better to use it unconditionally.
Additionally, unused macro c99_signbit is deleted, which is also apparently broken because there is no signbitl() in C99.

Can you specify more precisely what you mean by previously and currently?

Sorry for my lack of explanation. These are based on this commit (c934219, which is based on blead's dba7cf2); I mean "before c934219" by previously and "as of c934219" by currently.

I looked at the code, and this commit looks to be the right thing to do