CXML 
  POPCNT (3sciport)
Counts the number of bits set to one
SYNOPSIS
  i = POPCNT( arg )
FUNCTION VALUE
  popcnt          Integer.
                  The number of one bits found in arg
ARGUMENTS
  arg             Integer, Logical, or Real.
                  The 64 bit input argument.
DESCRIPTION
  The external integer function POPCNT returns the count of ones found in
  arg.
  For equations and other information, see Volume 3: UNICOS Math and
  Scientific Library Reference Manual SR-2081 7.0, Cray Research, Inc.
NOTES
  Since POPCNT is not an ANSI Fortran 77 intrinsic function, it must be
  declared as an external function of type integer. For example:
          EXTERNAL POPCNT
          INTEGER  POPCNT
          ...
          I = POPCNT( 'CCCCCCCCCCCCCCCC'X )       ! Same as I = 32
 
  
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