def coerce_nc3_dtype(arr):
    """Coerce an array to a data type that can be stored in a netCDF-3 file

    This function performs the following dtype conversions:
        int64 -> int32
        bool -> int8

    Data is checked for equality, or equivalence (non-NaN values) with
    `np.allclose` with the default keyword arguments.
    """
    dtype = str(arr.dtype)
    if dtype in _nc3_dtype_coercions:
        new_dtype = _nc3_dtype_coercions[dtype]
        # TODO: raise a warning whenever casting the data-type instead?
        cast_arr = arr.astype(new_dtype)
        if not (cast_arr == arr).all():
            raise ValueError('could not safely cast array from dtype %s to %s'
                             % (dtype, new_dtype))
        arr = cast_arr
    return arr