On Wed, Jun 17, 2026 at 10:30:56PM +0100, David Laight wrote: > On Wed, 17 Jun 2026 14:56:09 +0200 > Johannes Berg <[email protected]> wrote: > > On Wed, 2026-06-17 at 13:12 +0200, Andy Shevchenko wrote: > > > Convert size_add() to take variadic argument, so we can simplify users > > > with using a macro only once. > > > > > +#define __size_add3(addend1, addend2, addend3, addend4, ...) > > > \ > > > + __size_add(__size_add2(addend1, addend2, addend3), addend4) > > > +#define __size_add4(addend1, addend2, addend3, addend4, addend5, ...) > > > \ > > > + __size_add(__size_add3(addend1, addend2, addend3, addend4), addend5) > > > > I guess it's not going to really matter, but it would generate fewer > > calls to have something more like > > > > #define __size_add3(a1, a2, a3, a4) \ > > size_add(size_add(a1, a2), size_add(a3, a4)) > > #define __size_add4(a1, a2, a3, a4, a5) \ > > size_add(size_add(a1, a2), size_add(a3, a4, a5)) > > > > as a binary tree, rather than only cutting one off every time. Not sure > > that results in hugely different code though - maybe fewer overflow > > checks?
Good question. I'm also thinking that one-by-one may expand in too much of preprocessor code (haven't checked myself). > The binary tree stands a chance of executing less slowly because the leaf > adds can be executed in parallel. > Excluding the saturation checks (wtf is it called size_add() not > saturating_add() ?) (a + b) + (c + d) will usually execute faster than > ((a + b) + c) + d because the (a + b) and (c + d) can execute at the > same time; unfortunately gcc will always generate the latter. I'm confused. "unfortunately... the latter"? You meant "the former"? > > Although your version make it really completely equivalent to the > > nl80211.c code, clearly it doesn't matter if all the values are "good", > > and I believe the overflow behaviour means it doesn't matter for the > > overflow case either? Indeed. Whenever the value is saturated, the rest is just matter of sequential unlikely branches taken. -- With Best Regards, Andy Shevchenko
