Function unpack_null

cpp/src/arrow/util/bpacking_dispatch_internal.h:35–37

/// Unpack a zero bit packed array.
template <typename Uint>
ARROW_FORCE_INLINE void unpack_null(const uint8_t* in, Uint* out, int batch_size) {
  std::memset(out, 0, batch_size * sizeof(Uint));
}

/// Unpack a packed array where packed and unpacked values have exactly the same number of
/// bits.