[Numpy-discussion] Behavior of rint?

[Matthew Brett]

Hi Chuck,

Thanks for the replies, they are very helpful.

On Fri, Jan 19, 2018 at 1:51 PM, Charles R Harris
<charlesr.harris at gmail.com> wrote:
>
>
> On Fri, Jan 19, 2018 at 6:41 AM, Charles R Harris
> <charlesr.harris at gmail.com> wrote:
>>
>>
>>
>> On Fri, Jan 19, 2018 at 3:30 AM, Matthew Brett <matthew.brett at gmail.com>
>> wrote:
>>>
>>> Hi,
>>>
>>> Sorry for my confusion, but I noticed (as a result of the discussion
>>> here [1]) that np.rint and the fallback C function [2] seem to round
>>> to even.  But - my impression was that C rint, by default, rounds down
>>> [3].   Is numpy rint not behaving the same way as the GNU C library
>>> rint?
>>>
>>> In [4]: np.rint(np.arange(0.5, 11))
>>> Out[4]: array([ 0.,  2.,  2.,  4.,  4.,  6.,  6.,  8.,  8., 10., 10.])
>>>
>>> In [5]: np.round(np.arange(0.5, 11))
>>> Out[5]: array([ 0.,  2.,  2.,  4.,  4.,  6.,  6.,  8.,  8., 10., 10.])
>>
>>
>> The GNU C documentation says that rint "round(s) x to an integer value
>> according to the current rounding mode." The rounding mode is determined by
>> settings in the FPU control word. Numpy runs with it set to round to even,
>> although, IIRC, there is a bug on windows where the library is not setting
>> those  bits correctly.
>
>
> Round to even is also the Python default rounding mode.

Do you mean that it is Python setting the FPU control word?  Or do we
set it?  Do you happen to know where that is in the source?  I did a
quick grep just now without anything obvious.

Cheers,

Matthew