mul_1</code>, and <code>mpn_submul_1</code>.
<li> Alpha 21164: Rewrite <code>mpn_mul_1</code>, <code>mpn_addmul_1</code>,
     and <code>mpn_submul_1</code> for the 21164.  This should use both integer
     multiplies and floating-point multiplies.  For the floating-point
     operations, the single-limb multiplier should be split into three 21-bit
     chunks, or perhaps even better in four 16-bit chunks.  Probably possible
     to reach 9 cycles/limb.
<li> Alpha: GCC 3.4 will introduce <code>__builtin_ctz