On Fri, Aug 07, 2009 at 11:40:58AM -0400, Tom Lane wrote: > Sam Mason <s...@samason.me.uk> writes: > > I would agree with Paul that EPSILON is a hack and probably should be > > removed. > > It's a hack but it's dealing with an extremely real problem, namely > the built-in inaccuracy of floating-point arithmetic. You can't just > close your eyes to that and hope that everything will be okay.
Yes, I know it's a fiddle to get right. Choosing the right primitives is generally the most difficult part. > A quick look through the geometry sources says that we might not be > critically dependent on anything except the assumption that two values > that aren't FPeq() will have a nonzero difference. Sorry, I'm struggling to parse that. I think it's all the double negatives. Are you saying that HYPOT() should really return zero when it's currently giving back would be FPzero? > (If you think this > is a tautology, you don't know enough about floating point arithmetic > to be qualified to offer an opinion here...) I think I have a reasonable idea about FP arithmetic, I have had to worry about rounding modes and such like before. Never tried to write a FP emulator though so I'm sure I could know more. -- Sam http://samason.me.uk/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
