[Python-Dev] testing the C API in the test suite (was: bug in PyLong_FromLongLong (PR#324)) (original) (raw)

Trent Mick trentm@activestate.com
Thu, 11 May 2000 15:14:45 -0700

Date: Wed, 10 May 2000 15:37:30 -0400 From: Thomas.Malik@t-online.de To: python-bugs-list@python.org cc: bugs-py@python.org Subject: [Python-bugs-list] bug in PyLongFromLongLong (PR#324)

FullName: Thomas Malik Version: 1.5.2 OS: all Submission from: p3e9ed447.dip.t-dialin.net (62.158.212.71)

there's a bug in PyLongFromLongLong, resulting in truncation of negative 64 bi t integers. PyLongFromLongLong starts with: if( ival <= (LONGLONG)LONGMAX ) { return PyLongFromLong( (long)ival ); } else if( ival <= (unsigned LONGLONG)ULONGMAX ) { return PyLongFromUnsignedLong( (unsigned long)ival ); } else { .... Now, if ival is smaller than -LONGMAX, it falls outside the long integer range (being a 64 bit negative integer), but gets handled by the first if-then-case i n above code ('cause it is, of course, smaller than LONGMAX). This results in truncation of the 64 bit negative integer to a more or less arbitrary 32 bit number. The way to fix it is to compare the absolute value of imax against LONGMAX in the first condition. The second condition (ULONGMAX) must, at least, check wether ival is positive.

To test this error I found the easiest way was to make a C extension module to Python that called the C API functions under test directly. I can't quickly think of a way I could have shown this error clearly at the Python level without a specialized extension module. This has been true for other things that I have been testing.

Would it make sense to create a standard extension module (called '__test' or something like that) in which direct tests on the C API could be made? This would be hooked into the standard testsuite via a test_capi.py that would:

Does something like this already exist that I am missing?

This would make testing some things a lot easier, and clearer. Where some interface is exposed to the Python programmer it is appropriate to test it at the Python level. Python also provides a C API and it would be appropriate to test that at the C level.

I would like to hear some people's thoughts before I go off and put anything together.

Thanks, Trent

-- Trent Mick trentm@activestate.com