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Date: Tue, 10 Apr 2018 15:50:07 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: catan errors
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.
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
View attachment "catan.diff" of type "text/plain" (688 bytes)
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