ck they've been <code>mp?_init</code>ed.  This might
     catch elementary mistakes in user programs.  Care would need to be taken
     over <code>MPZ_TMP_INIT</code>ed variables used internally.  If nothing
     else then consistency checks like size&lt;=alloc, ptr not
     <code>NULL</code> and ptr+size not wrapping around the address space,
     would be possible.  A more sophisticated scheme could track
     <code>_mp_d</code> pointers and ensure only a valid one is used.  Such a
     scheme probably wo