Sam Mason <sam(at)samason(dot)me(dot)uk> writes:
> On Fri, Aug 07, 2009 at 12:50:39PM -0400, Tom Lane wrote:
>> No, I'm worried about code that supposes that it can divide by (x - y)
>> after testing that FPeq(x,y) is not true. point_sl() for instance.
> OK, but I'm still not sure what you're getting at.
Underflow. x!=y does not imply (x-y) != 0, if x and y are sufficiently
small and close together. The difference could underflow to zero.
regards, tom lane