Re: [eigen] Signed or unsigned indexing 
[ Thread Index  Date Index  More lists.tuxfamily.org/eigen Archives ]
Hi Benoit, Thanks for your notes on undefined behaviour which are quite interesting, especially the "switch" one that looks scary. But we always come back to those "nasal deamons" and these stories around the big bad wolf that you hear a lot but you never really get in real life. Yes, with undefined behaviour, anything can happen, but I believe that it should be seen from a practical point of view: 1 Do we know of any disaster (such as Ariane 5) that could have been avoided using signed or unsigned integers? 2 Do we know of any security flaw that could have been avoided using signed or unsigned integers? 3 Do we know of any bugs that could have been avoided using signed or unsigned integers? For the third question, my answer is yes. I've heard of so many bugs caused by a misuse of unsigned integers that could have been avoided by using signed integers. Now, I understand that you are concerned about the answers to question 1 and 2. I understand why people could be scared of "undefined behaviour". But I would like to get some concrete examples of things that really went wrong because of the usage of signed integers. I've never seen any, but I have to admit that I don't have any experience in security. If you look at the CERT C coding standard, they are equally concerned about warping behaviour of unsigned integers and undefined behaviour of signed integers. As a side note, I would be more concerned about the fact that Eigen does not use any error reporting mechanism. For instance, I have no idea what could happen when I ask a Cholesky decomposition on a matrix that is symmetric but not positive. And it is not something that could be easily checked before asking for the decomposition. François

Mail converted by MHonArc 2.6.19+  http://listengine.tuxfamily.org/ 