fix undefined float behaviour in pack('f')

The C standard says that the value of the expression (float)double_var is
undefined if 'the value being converted is outside the range of values
that can be represented'.

So to shut up -fsanitize=undefined:

    my $p = pack 'f', 1.36514538e67;

giving

    runtime error: value 1.36515e+67 is outside the range of representable values of type 'float'

explicitly handle the out of range values.
Something similar is already done under defined(VMS) && !defined(_IEEE_FP),
except that there it floors to +/- FLT_MAX rather than +/- (float)NV_INF.
I don't know which branch is best, and whether they should be merged.

This fix was suggested by Aaron Crane.

1 files changed, 4 insertions, 1 deletions

diff --git a/pp_pack.c b/pp_pack.c
index ad4f186bf9..9ed8c59714 100644
--- a/pp_pack.c
+++ b/pp_pack.c
@@ -2719,7 +2719,10 @@ S_pack_rec(pTHX_ SV *cat, tempsym_t* symptr, SV **beglist, SV **endlist )
 		    afloat = -FLT_MAX;
 		else afloat = (float)anv;
 # else
-		afloat = (float)anv;
+                /* a simple cast to float is undefined if outside
+                 * the range of values that can be represented */
+		afloat = (float)(anv >  FLT_MAX ?  NV_INF :
+                                 anv < -FLT_MAX ? -NV_INF : anv);
 # endif
                 PUSH_VAR(utf8, cur, afloat, needs_swap);
 	    }