The functions `modulo_floor`, `modulo_ceil`, `div_floor` and `div_ceil` of the `integer_functions` exhibit unclear rounding behaviour. Their names and docstrings indicate mathematical rounding behaviour ("down" is negative infinity), while their implementation performs zero-oriented rounding ("down" is toward zero), as this is the default behaviour of C `/` and `%`. We should clarify the semantics of these functions and adapt docstring, implementation, or both. See also the discussion here: pycodegen/pystencils!368