class HBArray: public TObject

 Bit array class

 Implements functions to create and manipulate array of bits. Functions
 to: dynamically create arrays, access (read and write) elements at
 a particular position, are provided.

 'Bits' are represented using  unsigned integer type, but minor changes
 are required to change this particular representation to other
 basic type such as unsigned char.
 The 'bit fields' are splitted according to the structure defined by
 the caller (link to the category setup). This splitting in sub-bitfields
 is done using a pointer array like structure.

 N.B: the bit array can not be a replacement of the standard library
 <bitset> ect.. :
 This class is mainly used to create the bit-based lookup table needed for
 random access of HDataObjects in the HBitFieldCategory container.
 For that purpose, efficient additional mathematical functions
 (complement, number of set bits)  have also been implemented.
 Nevertheless, the extension of the bit array interface to a more
 complete/general one is of course possible


 typedef names used
     => including  definitions of the following 3 types
              elem_t = a number (used as a count, i.e. never < 0,
                                throughout).
               bit  = an unsigned integer
                      + If this is not UChar_t then the #define
                        of BITS_SZ as CHAR_BIT should be changed.
                      + If this is not internally represented by 8
                         bits then the lookup table in the methods
                               Int_t  HBArray::bcount()
                               Int_t  HBArray::bcount2()
                         must be replaced.