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  19 </p><div class="section" title="Design"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="allocator.bitmap.design"></a>Design</h2></div></div></div><p>
  20     As this name suggests, this allocator uses a bit-map to keep track
  21     of the used and unused memory locations for its book-keeping
  22     purposes.
  23   </p><p>
  24     This allocator will make use of 1 single bit to keep track of
  25     whether it has been allocated or not. A bit 1 indicates free,
  26     while 0 indicates allocated. This has been done so that you can
  27     easily check a collection of bits for a free block. This kind of
  28     Bitmapped strategy works best for single object allocations, and
  29     with the STL type parameterized allocators, we do not need to
  30     choose any size for the block which will be represented by a
  31     single bit. This will be the size of the parameter around which
  32     the allocator has been parameterized. Thus, close to optimal
  33     performance will result. Hence, this should be used for node based
  34     containers which call the allocate function with an argument of 1.
  35   </p><p>
  36     The bitmapped allocator's internal pool is exponentially growing.
  37     Meaning that internally, the blocks acquired from the Free List
  38     Store will double every time the bitmapped allocator runs out of
  39     memory.
  40   </p><p>
  41     The macro <code class="literal">__GTHREADS</code> decides whether to use
  42     Mutex Protection around every allocation/deallocation. The state
  43     of the macro is picked up automatically from the gthr abstraction
  44     layer.
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