On Thursday, 18 December 2008 at 15:12, Rocco Rutte wrote: > Hi, > > * Brendan Cully wrote: > >> http://dev.mutt.org/hg/mutt/rev/7b46e23ae476 >> changeset: 5607:7b46e23ae476 >> branch: HEAD >> user: Erik Hovland <e...@hovland.org> >> date: Tue Dec 16 12:53:19 2008 -0800 >> summary: Remove redundant int clamping > > I think this change is actually wrong. The sign of a%b in C is > machine-dependent for negative values. Thus, > > h = (h * SOMEPRIME) % n; > h = (h >= 0) ? h : h + n; > > ensures that h is always positive. So at least the former line needs to > go in again or it must be sure that the final return value is in the > range 0..n-1.
Sorry, I forgot to reply to this earlier. I think since h is now unsigned, h * SOMEPRIME is unsigned and so (h * SOMEPRIME) % n will also be signed. (n should never be negative -- I am not sure why it isn't typed as unsigned). We might also want to use a better hash function -- there are many available. In fact, I'll look into that now.
