def page_to_offset(params):
    """
    Transforms `page`/`per_page` from `params` to `limit`/`offset` suitable for SQL.

    :param dict params: The dictionary containing `page` and `per_page` values will be added
                        the values `limit` and `offset`.
    """
    if 'page' not in params:
        return
    page = params['page']
    del params['page']
    if 'per_page' in params:
        per_page = params.get('per_page')
        del params['per_page']
    else:
        per_page = params.get('limit', 10)
    params['offset'] = int(per_page) * (int(page) - 1)
    params['limit'] = per_page
