y incorrect, as it
 is lower than the correct value computed by the MPFI library.
<p>

The value computed by the SSE2 (5) is much more precise than the one
computed by the x87. Unfortunately, there is no way to get an upper and 
lower bound value, and we are thus stuck with the x87 for computing these 
(sometimes incorrect) bounds.
<p>

The problem here is that the value computed by the standard, C-lib (or ocaml)
cos function doesn't always lie in the lower/upper bound interval returned by 
the x87 function