[Numpy-discussion] Bizarre errors with byteswapping, complex256, PPC
Travis Oliphant
travis at continuum.io
Wed Jun 20 16:56:08 EDT 2012
This looks like a problem with comparisons of floating point numbers rather than a byteswapping problem per-say. Try to use an almost equal comparison instead.
-Travis
On Jun 20, 2012, at 3:48 PM, Matthew Brett wrote:
> Hi,
>
> Our Debian friends were hammering our code tests before the upcoming
> freeze, and found the following very odd thing on 32-bit PPC running
> Debian squeeze and numpy 1.6.2 or current trunk.
>
> Consider the following script:
>
> <script>
> import numpy as np
>
> arr = np.arange(10, dtype=np.complex256)
> bs_arr = arr.byteswap().newbyteorder('S')
> print arr
> print bs_arr
> print arr == bs_arr
> print arr == bs_arr
> print arr == bs_arr
> </script>
>
> Here is the output from some example runs of this script:
>
> np-devel)[mb312 at joshlegacy ~/tmp]$ python funny_bs.py
> [ 0.0+0.0j 1.0+0.0j 2.0+0.0j 3.0+0.0j 4.0+0.0j 5.0+0.0j 6.0+0.0j
> 7.0+0.0j 8.0+0.0j 9.0+0.0j]
> [ 0.0+0.0j 1.0+0.0j 2.0+0.0j 3.0+0.0j 4.0+0.0j 5.0+0.0j 6.0+0.0j
> 7.0+0.0j 8.0+0.0j 9.0+0.0j]
> [ True False False False False False False False False False]
> [ True False False False False False False False False False]
> [ True False False False False False False False False False]
>
> (that's the most common result)
>
> (np-devel)[mb312 at joshlegacy ~/tmp]$ python funny_bs.py
> [ 0.0+0.0j 1.0+0.0j 2.0+0.0j 3.0+0.0j 4.0+0.0j 5.0+0.0j 6.0+0.0j
> 7.0+0.0j 8.0+0.0j 9.0+0.0j]
> [ 0.0+0.0j 1.0+0.0j 2.0+0.0j 3.0+0.0j 4.0+0.0j 5.0+0.0j 6.0+0.0j
> 7.0+0.0j 8.0+0.0j 9.0+0.0j]
> [ True True True True True True True True True True]
> [ True True True True True True True True True True]
> [ True True True True True True True True True True]
>
> (this happens maybe 10% of the time)
>
> (np-devel)[mb312 at joshlegacy ~/tmp]$ python funny_bs.py
> [ 0.0+0.0j 1.0+0.0j 2.0+0.0j 3.0+0.0j 4.0+0.0j 5.0+0.0j 6.0+0.0j
> 7.0+0.0j 8.0+0.0j 9.0+0.0j]
> [ 0.0+0.0j 1.0+0.0j 2.0+0.0j 3.0+0.0j 4.0+0.0j 5.0+0.0j 6.0+0.0j
> 7.0+0.0j 8.0+0.0j 9.0+0.0j]
> [ True True True True True True True True True True]
> [ True False False False False False False False False False]
> [ True True True True True True True True True True]
>
> (less than 10% of the time - order of True, False prints _of the same
> comparison_ is random. This only seems to happen with complex256.
>
> Is there anything I can do to debug this further? Does anyone want a
> login to this machine to have a look?
>
> See you,
>
> Matthew
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