make perl core quiet under -Wfloat-equal

The gcc option -Wfloat-equal warns when two floating-point numbers
are directly compared for equality or inequality, the idea being that
this is usually a logic error, and that you should be checking that the
values are instead very near to each other.

perl on the other hand has lots of reasons to do a direct comparison.

Add two macros, NV_eq_nowarn(a,b) and NV_eq_nowarn(a,b)
that do the same as (a == b) and (a != b), but without the warnings.
They achieve this by instead doing (a < b) || ( a > b).
Under gcc at least, this is optimised into the same code as the direct
comparison.

The are three places that I've left untouched, because they are handling
NaNs, and that gets a bit tricky. In particular (nv != nv) is a test for a
NaN, and replacing it with (< || >) creates signalling NaNs (whereas ==
and != create quiet NaNs)

1 files changed, 1 insertions, 1 deletions

diff --git a/pp_sys.c b/pp_sys.c
index 78308f44ab..92d4c608f6 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -4466,7 +4466,7 @@ PP(pp_gmtime)
     else {
 	NV input = Perl_floor(POPn);
 	when = (Time64_T)input;
-	if (when != input) {
+	if (NV_ne_nowarn(when, input)) {
 	    /* diag_listed_as: gmtime(%f) too large */
 	    Perl_ck_warner(aTHX_ packWARN(WARN_OVERFLOW),
 			   "%s(%.0" NVff ") too large", opname, input);