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Date: Thu, 07 Jan 2021 12:17:33 +0100
Message-Id: <mwpn2hm1wy.fsf@tomate.loria.fr>
From: Paul Zimmermann <Paul.Zimmermann@inria.fr>
To: musl@lists.openwall.com
Subject: [musl] issue with exp10l

       Hi,

I am extending my comparison of the accuracy of several mathematical libraries
to the "double extended precision" (long double on x86_64).

First I notice that Musl does not provide j0, j1, y0, and y1 for the long
double format. Do you confirm?

Then I got a segmentation fault using exp10l with NaN input with a non-zero
payload.

$ cat test_exp10.c
#define _GNU_SOURCE

typedef union { __uint128_t n; long double x; } union_t;

#include <stdio.h>
#include <math.h>
int main()
{
  union_t u;
  u.n = 16383UL;
  u.n = u.n << 64;
  u.n = u.n | 629329181547216221UL;
  /* u.n = 302213637488765131341149 */
  long double x = u.x;
  printf ("x=%La\n", x);
  fflush (stdout);
  long double y;
  y = exp10l (x);
  printf ("y=%La\n", y);
  fflush (stdout);
  return 0;
}

With glibc this works fine:

$ gcc -fno-builtin test_exp10.c -lm
$ ./a.out
x=nan
y=-nan

With Musl 1.2.1 I get:

$ ./a.out
x=nan
Segmentation fault

According to gdb, the issue is in pow10l:

Program received signal SIGSEGV, Segmentation fault.
0x000055555555d10e in pow10l ()
(gdb) where
#0  0x000055555555d10e in pow10l ()
#1  0x0000000080000000 in ?? ()
#2  0x0000000000003fff in ?? ()
#3  0x0000000000000000 in ?? ()

Best regards,
Paul