or.  A large block is defined to
be one larger than half of <TT>HBLKSIZE</tt>, which is a power of 2,
typically on the order of the page size.
<P>
Large block sizes are rounded up to
the next multiple of <TT>HBLKSIZE</tt> and then allocated by
<TT>GC_allochblk</tt>.  Recent versions of the collector
use an approximate best fit algorithm by keeping free lists for
several large block sizes.
The actual
implementation of <TT>GC_allochblk</tt>
is significantly complicated by black-listing issues
(see below).
<P>