On Mon, Feb 15, 2021 at 11:30:25PM -0800, Xie He wrote: > On Mon, Feb 15, 2021 at 10:04 PM Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > > > On Mon, Feb 15, 2021 at 11:08:02AM -0800, Xie He wrote: > > > On Mon, Feb 15, 2021 at 10:54 AM Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > > > > > > > On Mon, Feb 15, 2021 at 09:23:32AM -0800, Xie He wrote: > > > > > On Mon, Feb 15, 2021 at 1:25 AM Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > > > > > > > > > > > > + /* When transmitting data: > > > > > > > + * first we'll remove a pseudo header of 1 byte, > > > > > > > + * then the LAPB module will prepend an LAPB header of at most 3 bytes. > > > > > > > + */ > > > > > > > + dev->needed_headroom = 3 - 1; > > > > > > > > > > > > 3 - 1 = 2 > > > > > > > > > > > > Thanks > > > > > > > > > > Actually this is intentional. It makes the numbers more meaningful. > > > > > > > > > > The compiler should automatically generate the "2" so there would be > > > > > no runtime penalty. > > > > > > > > If you want it intentional, write it in the comment. > > > > > > > > /* When transmitting data, we will need extra 2 bytes headroom, > > > > * which are 3 bytes of LAPB header minus one byte of pseudo header. > > > > */ > > > > dev->needed_headroom = 2; > > > > > > I think this is unnecessary. The current comment already explains the > > > meaning of the "1" and the "3". There's no need for a reader of this > > > code to understand what a "2" is. That is the job of the compiler, not > > > the human reader. > > > > It is not related to compiler/human format. If you need to write "3 - 1" > > to make it easy for users, it means that your comment above is not > > full/correct/e.t.c. > > My point is: there is no need for human programmers / code readers to > understand what this "2" is. There is no need to explain what this "2" > means in the comment. There is no need to write this "2" in the code. > There is no need for this "2" to appear anywhere. That is just an > intermediate result generated by the compiler. It is similar to > assembly or machine code. It is generated by the compiler. Human > programmers just don't care about this intermediate result. > > My point could be more apparent if you consider a more complex > situation: "3 - 1 + 2 + 4 + 2". No human would want to see a > meaningless "10" in the code. We want to see the meaning of the > numbers, not a meaningless intermediate calculation result. Right, and we are using defines for that. Thanks
