message: bitmap: add method to get count
diff: #ifndef DH_BITMAP_H
  #define DH_BITMAP_H
  -#include <stdint.h>
  -#include <stdio.h>
  -#include <stdlib.h>
  -#include <string.h>
  +#include <cstdint>
  +#include <cstdio>
  +#include <cstdlib>
  +#include <cstring>
  #include "internal.h"
  #include "staticlog.h"
  @@ -81,6 +81,14 @@ public:
  return result;
  }
  + inline uint64_t inUseCount() const {
  + uint64_t count = 0;
  + for (size_t i = 0; i < _elements/WORDBITS; i++) {
  + count += __builtin_popcountl(_bitarray[i]);
  + }
  + return count;
  + }
  +
  private:
  /// Given an index, compute its item (word) and position within the word.
  void computeItemPosition(unsigned long long index, unsigned int &item, unsigned int &position) const {
  