On Thu, 15 Feb 2024 08:45:52 +0900 Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote: > > Hmm, the above is a fast path. I wonder if we should add a patch to make that into: > > > > if (unlikely(size_bytes & (sizeof(long) - 1))) > > data_size = DIV_ROUND_UP(size_bytes, sizeof(long)); > > else > > data_size = size_bytes >> (sizeof(long) == 4 ? 2 : 3); > > > > to keep from doing the division. > > OK, I thought DIV_ROUND_UP was not much cost. Since sizeof(long) is > fixed 4 or 8, so > > data_size = (size_bytes + sizeof(long) - 1) >> BITS_PER_LONG; > > will this work? No, because BITS_PER_LONG is 32 or 64 ;-) But this should; data_size = (size_bytes + sizeof(long) - 1) >> (sizeof(long) == 4 ? 2 : 3); As sizeof(long) is a constant, that conditional expression will be hard coded into either 2 or 3 by the compiler. -- Steve
