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Re: pi/2 again...
- From: David Miller <davem at davemloft dot net>
- To: joseph at codesourcery dot com
- Cc: libc-alpha at sourceware dot org
- Date: Thu, 02 May 2013 16:35:07 -0400 (EDT)
- Subject: Re: pi/2 again...
- References: <20130502 dot 152322 dot 1341414586375955556 dot davem at davemloft dot net> <Pine dot LNX dot 4 dot 64 dot 1305022015520 dot 12072 at digraph dot polyomino dot org dot uk>
From: "Joseph S. Myers" <joseph@codesourcery.com>
Date: Thu, 2 May 2013 20:21:37 +0000
> pi/2 rounded to nearest for ldbl-128 is
> 0x1.921fb54442d18469898cc51701b8p+0L (computed with MPFR). The cosine of
> that value, again rounded to nearest, is
> 0x3.9a252049c1114cf98e804177d4c8p-116L.
>
> That cosine is exactly the value currently expected in libm-test.inc (but
> MPFR prefers a different exponent when displaying it). If M_PI_2l, shown
> as a hex float, is equal to the value given above, then you have a problem
> with the ldbl-128 cos function being inaccurate near pi/2 (maybe a range
> reduction issue) - which will need filing as such in Bugzilla and fixing.
M_PI_2l is printed as a hex float equal to the value above so it's a cos()
issue, bugzilla filed.