On 05.02.20 13:51, Segher Boessenkool wrote: > On Tue, Feb 04, 2020 at 02:38:51PM +0100, David Hildenbrand wrote: >> On 04.02.20 14:13, Segher Boessenkool wrote: >>> On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote: >>>> It's a pattern commonly used in compilers and emulators to calculate the >>>> number of bytes to the next block/alignment. (we're missing a macro >>>> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up >>>> with a good name (e.g., SIZE_TO_NEXT_ALIGN) . > >>> You can just write the easy to understand >>> >>> ... ALIGN_UP(x) - x ... >> >> you mean >> >> ALIGN_UP(x, PAGES_PER_SECTION) - x >> >> but ... >> >>> which is better *without* having a separate name. Does that not >>> generate good machine code for you? >> >> 1. There is no ALIGN_UP. "SECTION_ALIGN_UP(x) - x" would be possible > > Erm, you started it ;-) Yeah, I was thinking in the wrong code base :) > >> 2. It would be wrong if x is already aligned. >> >> e.g., let's use 4096 for simplicity as we all know that value by heart >> (for both x and the block size). >> >> a) -(4096 | -4096) -> 4096 >> >> b) #define ALIGN_UP(x, a) ((x + a - 1) & -(a)) >> >> ALIGN_UP(4096, 4096) - 4096 -> 0 >> >> Not as easy as it seems ... > > If you always want to return a number >= 1, it it simply > ALIGN_UP(x + 1) - x I'm sorry to have to correct you again for some corner cases: ALIGN_UP(1, 4096) - 4096 = 0 Again, not as easy as it seems ... -- Thanks, David / dhildenb
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