On Fri, Nov 6, 2015 at 7:18 AM, Stepan Kasal <ka...@ucw.cz> wrote: > Hello, > > I was learning Cython from this tutorial when I noticed a glitch: > > Near the end, after boundscheck False, some variables are changed to > unsigned int. But this has unexpected consequences: variables t_from and such > are not determined correctly, as one of the arguments is negative, but gets > cast to unsigned for comaprison. (Yes, this is a weird feature of C.) > > Actually, the use of unsigned does not seem to have any impact on performance, > so I suggest to scratch that part of tutorial. Just explain that with > boundscheck > off, negaitive indices no longer work. > > (But there might perhaps be one small improvent in cython itself: with > boundscheck > off, the index might be cast to unsigned before it is used: this way we > probably > crash on negative values, instead of silently accessing the negative offset of > the array data.)
There's two directives: wraparound and boundscheck. The wraparound directive can be used to disable the check for negative values. I heartily agree that using unsigned types is the source of much surprising pain, we shouldn't be recommending it: https://github.com/cython/cython/commit/06f75b803d91805f3068bbad2b9241efbd5cdc44 _______________________________________________ cython-devel mailing list cython-devel@python.org https://mail.python.org/mailman/listinfo/cython-devel
