class THnSparseT<TArrayD>: public THnSparse

 THnSparseCompactBinCoord is a class used by THnSparse internally. It
 represents a compacted n-dimensional array of bin coordinates (indices).
 As the total number of bins in each dimension is known by THnSparse, bin
 indices can be compacted to only use the amount of bins needed by the total
 number of bins in each dimension. E.g. for a THnSparse with
 {15, 100, 2, 20, 10, 100} bins per dimension, a bin index will only occupy
 28 bits (4+7+1+5+4+7), i.e. less than a 32bit integer. The tricky part is
 the fast compression and decompression, the platform-independent storage
 (think of endianness: the bits of the number 0x123456 depend on the
 platform), and the hashing needed by THnSparseArrayChunk.

This class is also known as (typedefs to this class)