 used for each k.
     Looking at a graph makes it fairly clear.
<li> <code>__gmp_doprnt_mpf</code> does a rather unattractive round-to-nearest
     on the string returned by <code>mpf_get_str</code>.  Perhaps some variant
     of <code>mpf_get_str</code> could be made which would better suit.
</ul>


<h4>Aids to Development</h4>
<ul>
<li> Add <code>ASSERT</code>s at the start of each user-visible mpz/mpq/mpf
     function to check the validity of each <code>mp?_t</code> parameter, in
     particular to che