STINNER Victor added the comment: Just to share my little experience with rounding numbers.
Last years, I worked on a API to convert timestamps between float and integers, the private "PyTime C API": https://haypo.github.io/pytime.html At the beginning, I used various floatting point numbers which looks fine in decimal. But quickly, I got rounding issues on various buildbots. After many years fighting against compilers and trying to write a complete test suite, I decided to only use numbers which can be stored exactly in IEEE 754: if use_float: # numbers with an exact representation in IEEE 754 (base 2) for pow2 in (3, 7, 10, 15): ns = 2.0 ** (-pow2) ns_timestamps.extend((-ns, ns)) If you are curious, look at CPyTimeTestCase, TestCPyTime and TestOldPyTime classes in Lib/test/test_time.py. At the end, I decided to reimplement each conversion function in pure Python using decimal.Decimal and compare the result with the C implementation. It makes the unit tests shorter and simpler. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue27761> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
