Re: lib/50698: hypotf() of small numbers yields infinity

[Andreas Gustafsson <gson%gson.org@localhost>]

The following reply was made to PR lib/50698; it has been noted by GNATS.

From: Andreas Gustafsson <gson%gson.org@localhost>
To: Rin Okuyama <okuyama%flex.phys.tohoku.ac.jp@localhost>
Cc: gnats-bugs%NetBSD.org@localhost
Subject: Re: lib/50698: hypotf() of small numbers yields infinity
Date: Fri, 11 Mar 2016 17:14:15 +0200

 On Feb 1, Rin Okuyama wrote:
 > On 2016/01/26 0:01, Andreas Gustafsson wrote:
 > >>   Other changes have been made for libm in FreeBSD. IMO, we should merge
 > >>   reasonable ones.
 > >
 > > Additional patches for the ones you think are reasonable are welcome.
 > > More test cases would be good, too.
 > 
 > Sorry for the late reply.
 
 Likewise :)
 
 > I examined FreeBSD's libm, and found it much
 > harder than I had imagined to merge their changes into ours.
 > 
 > There are three kinds of differences: (1) trivial bug fixes as in this
 > case, (2) long double functions missing in our libm, and (3) non-trivial
 > changes to improve the accuracy or processing speed.
 > 
 > We can readily merge (1) by patiently comparing the two implementations.
 > 
 > For (2), we have not fully implemented long double functions. Instead,
 > we have wrappers to double functions in src/lib/libm/src/ldbl_dummy.c.
 > Needless to say, this is problematic for architectures with
 > LDBL_MANT_DIG != DBL_MANT_DIG. They have long double functions both for
 > LDBL_MANT_DIG == 64 (amd64, i386, ia64, and m68k), and 113 (aarch64,
 > mips64, and sparc64). If we can merge it, we then have long double
 > functions for all architectures except powerpc64 (LDBL_MANT_DIG == 106).
 > 
 > However, for (2) and (3), there remains a big problem; how can we test
 > them? Addition to ATF-based tests ported from us, they have their own
 > test cases:
 > 
 >    https://svnweb.freebsd.org/base/head/lib/msun/tests/
 > 
 > Function returns for some special arguments are checked in their test.
 > But is it enough? Who can check hundreds of magic numbers?
 
 These are all good questions, but I'm afraid I don't have the answers.
 In any case, the specific bug reported in this PR has now been fixed
 and pulled up to -7, so I will close the PR.  If you have suggestions
 for additional tests or fixes, either for hypotf() or for libm in
 general, feel free to submit them as separate PRs.
 -- 
 Andreas Gustafsson, gson%gson.org@localhost