lib/49256: exp2f subtests 9 and 10 of lib/libm/t_exp/exp2_values test case failing

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         49256
>Category:       lib
>Synopsis:       exp2f subtests 9 and 10 of lib/libm/t_exp/exp2_values test case failing
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Oct 04 18:05:00 +0000 2014
>Originator:     Andreas Gustafsson
>Release:        NetBSD-curent, source date >= 2014.03.16.22.51.19
>Organization:
>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

Subtests 9 and 10 of the exp2_values test case have failed in every
run since they were added in src/tests/lib/libm/t_exp.c revision 1.6
on CVS date 2014.03.16.22.51.19.

Log messages from a recent failure:

  *** Check failed: subtest 9: exp2f(7.7) is 207.937 (0xc.fefc4000000000p+4) not 207.937 (0xc.fefc5e67299f0p+4), error 2.89945e-05 (0xf.3394d0p-19) > 2.28882e-05
  *** Check failed: subtest 10: exp2f(8.8) is 445.722 (0xd.edc69000000000p+5) not 445.722 (0xd.edc66d6df0920p+5), error 6.59381e-05 (0x8.a483dcp-17) > 4.57764e-05

The commit message for the test cases notes that "exp2f(7.7) and
exp2f(8.8) seem too far from their expected values (especially the
latter)".

The tests fail on all three archs being tested using qemu on the TNF
testbed (i386, amd64, and sparc), and also when running on the bare
metal (tested on amd64), so it's not a qemu issue; I'm assuming it's
an actual bug in libm.

>How-To-Repeat:

Run the ATF tests.

>Fix: