Thanks for the quick explanation & answers. I was mostly puzzled by the absence of warning. In C you would get an overflow warning in such a case, no ?
Nicolas > On 3 Jul 2019, at 20:01, Charles R Harris <charlesr.har...@gmail.com> wrote: > > > > On Wed, Jul 3, 2019 at 11:39 AM Matthew Brett <matthew.br...@gmail.com> wrote: > Hi, > > On Wed, Jul 3, 2019 at 9:08 AM Charles R Harris > <charlesr.har...@gmail.com> wrote: > > > > > > > > On Wed, Jul 3, 2019 at 9:08 AM Hameer Abbasi <einstein.edi...@gmail.com> > > wrote: > >> > >> Hi, > >> > >> It turns out you're running into a bit-error. In general, the two's > >> complement of -2 ** (n-1) with the bit-length being limited to n bits is > >> itself... No way around that. And integers don't set hardware exceptions > >> so checking for errors like these is hard as well. > >> > >> TL;DR: It's an error with how the integer is stored in memory and how > >> you're running out of space. > >> > >> Regards, > >> Hameer Abbasi > > > > > > More like the eight bit twos complement of -128 is -128, bytes cannot > > represent 128. Matlab used to (still does?) solve this problem by returning > > 127 instead :) Basically, the data needs more precision. Returning an > > unsigned type would lead to it's own problems with unexpected promotions > > when the result was used. We could, I suppose, raise a warning, although > > that might be considered noisy. If you use `absolute` instead, you can > > specify the dtype. > > I still think this is a major wart in numpy's abs. > > I'd really like to add a new function, `uabs` which would return an > unsigned int for integer inputs. I'm happy to do a pull request if > that also seems sensible to y'all, > > > Seems reasonable, it would provide something for discussion. Note that the > current abs is in the slot provided by Python numeric types. The main problem > is that as soon as the unsigned result is combined with a signed type it will > get promoted. Which would not be much of a problem except int64 -> double. > > Chuck > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@python.org https://mail.python.org/mailman/listinfo/numpy-discussion
