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From: Szabolcs Nagy <nsz@port70.net>
To: musl@lists.openwall.com
Subject: Re: correctly rounded sqrt
Date: Thu, 15 Mar 2012 04:23:04 +0100	[thread overview]
Message-ID: <20120315032304.GJ5728@port70.net> (raw)
In-Reply-To: <20120315014647.GI5728@port70.net>

* Szabolcs Nagy <nsz@port70.net> [2012-03-15 02:46:48 +0100]:
> /* dekker exact mult u*u == hi + lo */
> static void sq(long double *hi, long double *lo, long double u)
> {
> 	static const long double c = 1.0 + 0x1p33;
this was wrong, c = 1.0 + 0x1p32; the correct value

and probably
*hi = u1*u1;
*lo = u1*u2*2.0 + u2*u2;
is enough instead of
> 	*hi = u*u;
> 	*lo = (u1*u1 - *hi) + u1*u2*2.0 + u2*u2;

but now that we figured out the fpu status register based
solution this does not matter..


  reply	other threads:[~2012-03-15  3:23 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-03-14 16:56 Szabolcs Nagy
2012-03-14 16:57 ` Szabolcs Nagy
2012-03-14 19:01 ` Szabolcs Nagy
2012-03-15  1:46   ` Szabolcs Nagy
2012-03-15  3:23     ` Szabolcs Nagy [this message]
2012-03-15  5:07       ` Rich Felker
2012-03-15  5:30         ` Szabolcs Nagy
2012-03-15  8:02           ` Szabolcs Nagy
2012-03-15 16:12             ` Rich Felker
2012-03-15 18:14               ` Pascal Cuoq
2012-03-15 18:22                 ` Szabolcs Nagy

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