From: "dgutson ." <danielgutson@gmail.com>
To: musl@lists.openwall.com
Subject: Re: catan errors
Date: Tue, 10 Apr 2018 17:23:12 -0300 [thread overview]
Message-ID: <CAFdMc-1cijofmRZoW+uS3D7higcYHVtuevX2Y2dT40Hegq2guw@mail.gmail.com> (raw)
In-Reply-To: <20180410195007.GI3094@brightrain.aerifal.cx>
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On Tue, Apr 10, 2018 at 4:50 PM, Rich Felker <dalias@libc.org> wrote:
> The OpenBSD catan implementation we're using has a number of
> nonsensical "overflow" (goto ovrf) conditions that aren't errors,
> reported by mepholic on irc. I think the attached patch fixes them
> without introducing new problems, but I'm not sure if any other
> problems remain.
>
> Note that, of the three cases removed:
>
> 1. Is not an exceptional case at all, and made no sense to begin with.
>
> 2. Is only exceptional if x and a are both zero; atan(2x,0) is
> perfectly well-defined.
>
> 3. Is only possible if y==1.0 and x==0.0, which is the only real
> exceptional case for atan: z==I.
>
Besides the trigonometric case, are you considering de-normalized numbers,
such as 4.94066e-324 as divisor?
For example:
double x = 1.0;
double y = 5E-324;
x / y is inf, and y != 0.0.
Shouldn't 'a' be checked against that number or its absolute value >=
minimum?
>
> I opted to replace the non-obvious (3) with an explicit check for z==I
> but this isn't necessary.
>
> As written the patch does not address raising exception flags; that
> should be fixed before it's committed but right now I'm just
> submitting this for comments.
>
> Prior to the patch, at least the following (utterly dumb -- the first
> is a very real input!) cases are broken:
>
> - catan(1.0)
> - catan(2*I)
> - catan(I)
>
> Rich
>
--
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One guess, that’s who?
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Who get stuck with all the bad luck?
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next prev parent reply other threads:[~2018-04-10 20:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-10 19:50 Rich Felker
2018-04-10 20:23 ` dgutson . [this message]
2018-04-10 20:32 ` Rich Felker
2018-04-10 20:41 ` dgutson .
2018-04-10 20:50 ` Rich Felker
2018-04-10 21:27 ` dgutson .
2018-04-10 22:14 ` Rich Felker
2018-04-10 23:08 ` Szabolcs Nagy
2018-04-10 23:23 ` Rich Felker
2018-04-11 0:52 ` Szabolcs Nagy
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