From: Paul Zimmermann <Paul.Zimmermann@inria.fr>
To: newlib@sourceware.org
Subject: hypotl
Date: Thu, 14 Jan 2021 08:13:23 +0100 [thread overview]
Message-ID: <mw1reouh2k.fsf@tomate.loria.fr> (raw)
Hi,
it seems newlib only provides sqrtl and hypotl for double extended precision
(long double on x86_64). Please can you confirm?
However the hypotl function seems buggy for large inputs, where it returns +Inf:
$ cat test_hypot.c
#include <stdio.h>
#include <math.h>
#ifdef NEWLIB
/* without this, newlib says: undefined reference to `__errno' */
int errno;
int* __errno () { return &errno; }
#endif
int main()
{
long double x = 0xf.ffffffffffffffep+8188l;
long double y = (long double) 0;
long double z = hypotl (x, y);
printf ("x=%La y=%La z=%La\n", x, y, z);
x = 0xf.fffffffffffffffp+8188l;
z = hypotl (x, y);
printf ("x=%La y=%La z=%La\n", x, y, z);
x = 0x1p+8192l;
z = hypotl (x, y);
printf ("x=%La y=%La z=%La\n", x, y, z);
return 0;
}
$ gcc -DNEWLIB test_hypot.c /localdisk/zimmerma/newlib-4.1.0/libm.a -lm
$ ./a.out
x=0xf.ffffffffffffffep+8188 y=0x0p+0 z=0xf.ffffffffffffffep+8188
x=0xf.fffffffffffffffp+8188 y=0x0p+0 z=-0xcp+16380
x=0x8p+8189 y=0x0p+0 z=inf
Note also the case x=0xf.fffffffffffffffp+8188 y=0x0p+0 where it returns an
ill-formed number.
Best regards,
Paul
reply other threads:[~2021-01-14 7:13 UTC|newest]
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