Extended precision

[uunet!cwi.nl!Dik.Winter]

 > The x87 is 100% IEEE compatible in its default mode.

Not having access to my references I wonder, but I think not.  Giving your
example (which by coincidence exactly matches my example as I posted
earlier), there are double precision numbers a and b such that when x
is double:
  x = a + b
will not yield the nearest result when using the default mode.
It gives 2^53+4, nearest would be 2^53+2.

dik