This flag has been set on startup since 65618fdda0.
However, This causes some of the math-related tests to fail as they report
zero instead of a tiny number. This fixes at least
/usr/tests/lib/msun/ldexp_test and possibly others.
Additionally, setting this flag prevents printf() from printing subnormal
numbers in decimal form.
See also https://www.openwall.com/lists/musl/2021/02/26/1
PR: 253847
Reviewed By: mmel
Differential Revision: https://reviews.freebsd.org/D28938
Don't exclude i386 from LDBL_MANT_DIG == 64; it works properly in
that case.
While here, replace strcmp + atf_tc_fail with ATF_CHECK_MSG for 2
reasons:
- Gather as many results as possible instead of failing early and
not testing the rest of the cases.
- Simplify logic when checking test inputs vs outputs and printing
test result.
Tested on: amd64, i386
MFC after: 1 week
Sponsored by: Dell EMC Isilon
