: <code>mpn_divrem_1</code> might be able to use a
     mul-by-inverse, hoping for maybe 30 c/l.
<li> K7: <code>mpn_lshift</code> and <code>mpn_rshift</code> might be able to
     do something branch-free for unaligned startups, and shaving one insn
     from the loop with alternative indexing might save a cycle.
<li> PPC32: Try using fewer registers in the current <code>mpn_lshift</code>.
     The pipeline is now extremely deep, perhaps unnecessarily deep.
<li> Fujitsu VPP: Vectorize main functions, perhap