[Python-Dev] Re: [snake-farm] test test_slice failed -- [9, 7, 5, 3, 1] == [0] (original) (raw)

Michael Hudson mwh@python.net
06 Nov 2002 11:04:57 +0000

Neal Norwitz <neal@metaslash.com> writes:

On Tue, Nov 05, 2002 at 10:38:18PM +0100, Anders Qvist wrote: > Between 1036491804 and 1036522446 (should be GMT 2002-11-05, 10:20 and > 2002-11-05, 18:54 respectively), testslice started failing with the > following message: > > test testslice failed -- [9, 7, 5, 3, 1] == [0] > > om moghedien; linux/alpha. There has been some changes containing > pointer arithmetic around line 160 of sliceobjects.c, which might be > guilty (just a shot in the dark; 64-bit clean?):

Oops! This is my fault.

It is a 64-bit problem, but doesn't have to do with the checkin to sliceobject. The new test (below) broke with old code too.

vereq(range(10)[::sys.maxint - 1], [0]) The problem is that sizeof(int) != sizeof(long). The parameters for PySliceGetIndices() and PySliceGetIndicesEx() take ints, not longs. So the code is doing: range(10)[::-2] since the high 32 bits are lost. The only solution I can think of is to have 2 interfaces: - the old API which takes int/int*, PySliceGetIndices() deprecate this API and raise overflow exception if (int)value != (long)value - the new API which takes long/long*, PySliceGetIndicesEx() PySliceGetIndicesEx() was added in 2.3.

So you suggest changing PySlice_GetIndicesEx(), right?

Otherwise, we are stuck with slices only being able to support 32 bits even on 64 bit architectures.

Other ideas?

I think the better idea is to call _PyEval_SliceIndex for the step element of the slice too. And maybe change the latter from

            else if (x < -INT_MAX)
                    x = 0;

to

            else if (x < -INT_MAX)
                    x = -INT_MAX;

Can you test this on a 64 bit platform or shall I just check it in?

Cheers, M.

-- After a heavy night I travelled on, my face toward home - the comma being by no means guaranteed. -- paraphrased from cam.misc