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Re: Fix ldbl-128 cos range reduction near pi/2 (bug 15429)
- From: David Miller <davem at davemloft dot net>
- To: joseph at codesourcery dot com
- Cc: libc-alpha at sourceware dot org
- Date: Thu, 09 May 2013 14:10:49 -0700 (PDT)
- Subject: Re: Fix ldbl-128 cos range reduction near pi/2 (bug 15429)
- References: <Pine dot LNX dot 4 dot 64 dot 1305091922380 dot 29757 at digraph dot polyomino dot org dot uk>
From: "Joseph S. Myers" <joseph@codesourcery.com>
Date: Thu, 9 May 2013 19:23:55 +0000
> Bug 15429 is inaccuracy of ldbl-128 cos near pi/2. The cause is
> inaccurate range reduction in that area; I don't know why the code
> uses only 93 bits for the high part of pi/2, but you need at least 226
> bits to get reasonable accuracy there, and subtraction of a 113-bit
> high part is always going to be exact in the relevant range. This
> patch changes the code to use 113 bits for both high and low parts.
> Tested mips64 to confirm the large ulps no longer appear.
Thanks a lot for working on this.