ut, rather than using it arithmetically, and those places
     might want to do their own loops entirely.
<li> <code>__gmp_extract_double</code> on 64-bit systems could use just one
     bitfield for the mantissa extraction, not two, when endianness permits.
     Might depend on the compiler allowing <code>long long</code> bit fields
     when that's the only actual 64-bit type.
<li> tal-notreent.c could keep a block of memory permanently allocated.
     Currently the last nested <code>TMP_FREE</code> relea