[Numpy-discussion] Bizarre errors with byteswapping, complex256, PPC

[Matthew Brett]

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@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@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@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