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Fix incorrect hypotl(3) result with subnormal numbers

Browse source 
This adjusts the factor used to scale the subnormal numbers, so it
becomes the right value after adjusting its exponent. Thanks to Steve
Kargl for finding the most elegant fix.

Also enable the hypot tests, and add a test case for this bug.

PR:		253313
MFC after:	1 week
This commit is contained in:
Dimitry Andric 2021-02-10 23:28:43 +01:00
parent a6dc68c0e0
commit d3338f3355
3 changed files with 22 additions and 1 deletions
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20
contrib/netbsd-tests/lib/libm/t_hypot.c
View file

@ -70,12 +70,32 @@ ATF_TC_BODY(pr50698, tc)
ATF_CHECK(!isnan(val));
}
ATF_TC(hypotl_near_underflow);
ATF_TC_HEAD(hypotl_near_underflow, tc)
{
atf_tc_set_md_var(tc, "descr", "Test hypotl near underflow");
}
ATF_TC_BODY(hypotl_near_underflow, tc)
{
volatile long double a = 0x1.b2933cafa0bb7p-16383L;
volatile long double b = 0x1.fffffffffffffp-16351L;
volatile long double e = 0x1.fffffffffffffp-16351L;
volatile long double ulp = __LDBL_EPSILON__;
volatile long double val = hypotl(a, b);
ATF_CHECK(!isinf(val));
ATF_CHECK(fabsl(val - e) <= 2 * ulp);
}
ATF_TP_ADD_TCS(tp)
{
ATF_TP_ADD_TC(tp, hypot_integer);
ATF_TP_ADD_TC(tp, hypotf_integer);
ATF_TP_ADD_TC(tp, pr50698);
ATF_TP_ADD_TC(tp, hypotl_near_underflow);
return atf_no_error();
}

2
lib/msun/src/e_hypotl.c
View file

@ -82,7 +82,7 @@ hypotl(long double x, long double y)
man_t manh, manl;
GET_LDBL_MAN(manh,manl,b);
if((manh|manl)==0) return a;
t1=0;
t1=1;
SET_HIGH_WORD(t1,ESW(MAX_EXP-2)); /* t1=2^(MAX_EXP-2) */
b *= t1;
a *= t1;

1
lib/msun/tests/Makefile
View file

@ -31,6 +31,7 @@ NETBSD_ATF_TESTS_C+= erf_test
NETBSD_ATF_TESTS_C+= exp_test
NETBSD_ATF_TESTS_C+= fmod_test
NETBSD_ATF_TESTS_C+= fe_round_test
NETBSD_ATF_TESTS_C+= hypot_test
NETBSD_ATF_TESTS_C+= infinity_test
NETBSD_ATF_TESTS_C+= ilogb_test
NETBSD_ATF_TESTS_C+= ldexp_test