Date: Sat, 6 Feb 2021 12:39:29 -0800 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: freebsd-current@freebsd.org Subject: hypothl(x) mishandles subnormal numbers. Message-ID: <20210206203929.GA45801@troutmask.apl.washington.edu>
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I've long forgotten by freebsd bugzilla password.
So, if someone would like to submit a bug report,
here's a test program.
% cc -o z -O2 -fno-builtin z.c -lm
% ./z
Via scaling and sqrtl
x=2.853684e-4932 y=1.444012e-4922 a=1.444012e-4922
x=0x1.b2933cafa0bb8p-16383 y=0x1.fffffffffffffp-16351 a=0x1.000000006ca4c8p-16350
Via hypotl
x=2.853684e-4932 y=1.444012e-4922 z=nan
x=0x1.b2933cafa0bb8p-16383 y=0x1.fffffffffffffp-16351 z=nan
% cat z.c
#include <stdio.h>
#include <math.h>
#if defined(__i386__)
#include <ieeefp.h>
#endif
int main()
{
long double x, y, z, a;
#if defined(__i386__)
fpsetprec(FP_PE);
#endif
x = 0x3.6526795f4176ep-16384L;
y = 0x3.ffffffffffffep-16352L;
z = hypotl(x, y);
if (x > y) {
a = y / x;
a = x * sqrtl(1 + a);
} else {
a = x / y;
a = y * sqrtl(a + 1);
}
printf("Via scaling and sqrtl\n");
printf("x=%Le y=%Le a=%Le\n", x, y, a);
printf("x=%La y=%La a=%La\n", x, y, a);
printf("\nVia hypotl\n");
printf("x=%Le y=%Le z=%Le\n", x, y, z);
printf("x=%La y=%La z=%La\n", x, y, z);
return 0;
}
--
Steve
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