[PACTH,libm] hypothl(x) mishandles subnormal numbers.

[Steve Kargl]

On Sat, Feb 06, 2021 at 10:32:33PM +0100, Dimitry Andric wrote:
> On 6 Feb 2021, at 22:04, Steve Kargl <sgk at troutmask.apl.washington.edu> wrote:
> > 
> > On Sat, Feb 06, 2021 at 12:39:29PM -0800, Steve Kargl wrote:
> >> I've long forgotten by freebsd bugzilla password.
> >> So, if someone would like to submit a bug report,
> >> here's a test program.
> >> 
> > Forgot to include that issue was identified from
> > a bug report in the OpenLibm bug mailing list.
> > 
> > https://github.com/JuliaMath/openlibm/issues/224
> 
> I put this in <https://bugs.freebsd.org/253313>. Now the trick is to
> figure out what is going on in e_hypotl.c... :)
> 

This patch fixes the issue.  t1 is used to scale the subnormal
numbers.  It is generated by scaling the exponent, but that 
only works if t1 is 1 not 0.

Index: src/e_hypotl.c
===================================================================
--- src/e_hypotl.c	(revision 2342)
+++ src/e_hypotl.c	(working copy)
@@ -82,7 +82,7 @@ hypotl(long double x, long double y)
 	        man_t manh, manl;
 		GET_LDBL_MAN(manh,manl,b);
 		if((manh|manl)==0) return a;
-		t1=0;
+		t1=1;
 		SET_HIGH_WORD(t1,ESW(MAX_EXP-2));	/* t1=2^(MAX_EXP-2) */
 		b *= t1;
 		a *= t1;


-- 
Steve