Date: Sat, 06 Feb 2021 21:29:02 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 253313] lib/msun: hypotl(3) mishandles subnormal numbers Message-ID: <bug-253313-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253313 Bug ID: 253313 Summary: lib/msun: hypotl(3) mishandles subnormal numbers Product: Base System Version: CURRENT Hardware: amd64 OS: Any Status: New Severity: Affects Some People Priority: --- Component: bin Assignee: bugs@FreeBSD.org Reporter: dim@FreeBSD.org >From https://github.com/JuliaMath/openlibm/issues/224, via Steve Kargl: Test program: ====================================================================== #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; } ====================================================================== Result on FreeBSD 14.0-CURRENT #0 main-n244563-d6f9c5a6d2f8 amd64: % cc -O2 -fno-builtin z.c -o z-amd64 -lm && ./z-amd64 Via scaling and sqrtl x=2.853684e-4932 y=1.444012e-4922 a=1.444012e-4922 x=0x1.b2933cafa0bb7p-16383 y=0x1.fffffffffffffp-16351 a=0x1.000000006ca4c72cp-16350 Via hypotl x=2.853684e-4932 y=1.444012e-4922 z=nan x=0x1.b2933cafa0bb7p-16383 y=0x1.fffffffffffffp-16351 z=nan On FreeBSD 14.0-CURRENT #0 main-n244563-d6f9c5a6d2f8 i386: % cc -O2 -fno-builtin z.c -o z-i386 -lm && ./z-i386 Via scaling and sqrtl x=2.853684e-4932 y=1.444012e-4922 a=1.444012e-4922 x=0x1.b2933cafa0bb7p-16383 y=0x1.fffffffffffffp-16351 a=0x1.000000006ca4c72cp-16350 Via hypotl x=2.853684e-4932 y=1.444012e-4922 z=nan x=0x1.b2933cafa0bb7p-16383 y=0x1.fffffffffffffp-16351 z=nan The expectation is that the results should be roughly similar, but at least hypotl should not produce nan in this case. With gcc 10.2 and not using -fno-builtin, the resulting assembly doesn't use *any* calls to libm, and produces: Via scaling and sqrtl x=2.853684e-4932 y=1.444012e-4922 a=1.444012e-4922 x=0x1.b2933cafa0bb7p-16383 y=0x1.fffffffffffffp-16351 a=0x1.000000006ca4c72cp-16350 Via hypotl x=2.853684e-4932 y=1.444012e-4922 z=1.444012e-4922 x=0x1.b2933cafa0bb7p-16383 y=0x1.fffffffffffffp-16351 z=0x1.fffffffffffffp-16351 clang 11.0 apparently doesn't have a built-in hypotl, so the output isn't different. -- You are receiving this mail because: You are the assignee for the bug.help
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