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 PyLong_FromLongLong (PR#324)

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

there's a bug in PyLong_FromLongLong, resulting in truncation of negative 64 bi t integers. PyLong_FromLongLong starts with: if( ival <= (LONG_LONG)LONG_MAX ) { return PyLong_FromLong( (long)ival ); } else if( ival <= (unsigned LONG_LONG)ULONG_MAX ) { return PyLong_FromUnsignedLong( (unsigned long)ival ); } else { ....

Now, if ival is smaller than -LONG_MAX, 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 LONG_MAX). 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 LONG_MAX in the first condition. The second condition (ULONG_MAX) 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: - import __test - run every exported function in __test (or everyone starting with 'test_', or whatever) - the ImportError could continue to be used to signify skipping, etc (although, I think that a new, more explicit TestSuiteError class would be more appropriate and clear) 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