1) TODO: I/O implementation in densehashtable.h

2) TODO: document SPARSEHASH_STAT_UPDATE macro, and also macros that
   tweak performance.  Perhaps add support to these to the API?

3) TODO: support exceptions?

4) BUG: sparsetable's operator[] doesn't work well with printf: you
   need to explicitly cast the result to value_type to print it.  (It
   works fine with streams.)

5) TODO: consider rewriting dense_hash_map to use a 'groups' scheme,
   like sparsetable, but without the sparse-allocation within a
   group.  This makes resizing have better memory-use properties.  The
   downside is that probes across groups might take longer since
   groups are not contiguous in memory.  Making groups the same size
   as a cache-line, and ensuring they're loaded on cache-line
   boundaries, might help.  Needs careful testing to make sure it
   doesn't hurt performance.

6) TODO: Get the C-only version of sparsehash in experimental/ ready
   for prime-time.

7) TODO: use cmake (www.cmake.org) to make it easy to isntall this on
   a windows system.

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28 February 2007