Re: kargl@freebsd.org, sgk@troutmask.apl.washington.edu, vincenzo.innocente@cern.ch, riemannic@gmail.com, johnmather@sidefx.com

       Hi Konstantin,

> Date: Tue, 6 Aug 2024 17:56:38 +0300
> From: Konstantin Belousov <kostikbel@gmail.com>
> Cc: hackers@freebsd.org, numerics@freebsd.org
> 
> On Tue, Aug 06, 2024 at 02:56:01PM +0200, Paul Zimmermann wrote:
> >        Hi,
> > 
> > we have updated our comparison with FreeBSD 14.1:
> > 
> > https://members.loria.fr/PZimmermann/papers/accuracy.pdf
> > 
> > Remaining issues in 14.1:
> > 
> > * the powl function is not thread-safe
> This is for 80-bit long double, am I right?

yes

> And it is because of the global vars passing values between functions?
> 
> I tried to hack something in https://reviews.freebsd.org/D46237

thanks. I tried to apply your patch on top of openlibm-0.8.3 (after
stripping lib/msun). Part of it failed:

$ patch -p1 -i /tmp/D46237.diff 
patching file ld80/e_powl.c
Hunk #1 FAILED at 23.
Hunk #2 FAILED at 42.
Hunk #3 succeeded at 85 (offset -41 lines).
Hunk #4 succeeded at 100 (offset -41 lines).
Hunk #5 succeeded at 135 (offset -41 lines).
Hunk #6 succeeded at 158 (offset -41 lines).
Hunk #7 succeeded at 189 (offset -41 lines).

$ cat ld80/e_powl.c.rej 
--- ld80/e_powl.c
+++ ld80/e_powl.c
@@ -23,10 +23,10 @@
  *  P[0] x^n  +  P[1] x^(n-1)  +  ...  +  P[n]
  */
 static inline long double
-__polevll(long double x, long double *PP, int n)
+__polevll(long double x, const long double *PP, int n)
 {
 	long double y;
-	long double *P;
+	const long double *P;
 
 	P = PP;
 	y = *P++;
@@ -42,10 +42,10 @@
  *  x^n  +  P[0] x^(n-1)  +  P[1] x^(n-2)  +  ...  +  P[n]
  */
 static inline long double
-__p1evll(long double x, long double *PP, int n)
+__p1evll(long double x, const long double *PP, int n)
 {
 	long double y;
-	long double *P;
+	const long double *P;
 
 	P = PP;
 	n -= 1;

Also I git compiler warnings (maybe due to the rejected part):

ld80/e_powl.c: In function ‘powl’:
ld80/e_powl.c:374:29: warning: passing argument 2 of ‘__polevll’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  374 | w = x * ( z * __polevll( x, P, 3 ) / __p1evll( x, Q, 3 ) );
      |                             ^

Apart from that, various tests I did seem to indicate the multi-thread issue
has gone, thanks!

Paul