On 06/03/2025 at 00:48, Andy Shevchenko wrote: > On Wed, Mar 05, 2025 at 11:48:10PM +0900, Vincent Mailhol wrote: >> On 05/03/2025 at 23:33, Andy Shevchenko wrote: >>> On Wed, Mar 05, 2025 at 10:00:16PM +0900, Vincent Mailhol via B4 Relay wrote: > > ... > >>>> +#define BIT_U8(b) (BIT_INPUT_CHECK(u8, b) + (unsigned int)BIT(b)) >>>> +#define BIT_U16(b) (BIT_INPUT_CHECK(u16, b) + (unsigned int)BIT(b)) >>> >>> Why not u8 and u16? This inconsistency needs to be well justified. >> >> Because of the C integer promotion rules, if casted to u8 or u16, the >> expression will immediately become a signed integer as soon as it is get >> used. For example, if casted to u8 >> >> BIT_U8(0) + BIT_U8(1) >> >> would be a signed integer. And that may surprise people. > > Yes, but wouldn't be better to put it more explicitly like > > #define BIT_U8(b) (BIT_INPUT_CHECK(u8, b) + (u8)BIT(b) + 0 + UL(0)) // + ULL(0) ? OK, the final result would be unsigned. But, I do not follow how this is more explicit. Also, why doing: (u8)BIT(b) + 0 + UL(0) and not just: (u8)BIT(b) + UL(0) ? What is that intermediary '+ 0' for? I am sorry, but I am having a hard time understanding how casting to u8 and then doing an addition with an unsigned long is more explicit than directly doing a cast to the desired type. As I mentioned in my answer to Yuri, I have a slight preference for the unsigned int cast, but I am OK to go back to the u8/u16 cast as it was in v3. However, I really do not see how that '+ 0 + UL(0)' would be an improvement. > Also, BIT_Uxx() gives different type at the end, shouldn't they all be promoted > to unsigned long long at the end? Probably it won't work in real assembly. > Can you add test cases which are written in assembly? (Yes, I understand that it will > be architecture dependent, but still.) No. I purposely guarded the definition of the BIT_Uxx() by a #if !defined(__ASSEMBLY__) so that these are never visible in assembly. I actually put a comment to explain why the GENMASK_U*() are not available in assembly. I can copy paste the same comment to explain why why BIT_U*() are not made available either: /* * Missing asm support * * BIT_U*() depends on BITS_PER_TYPE() which would not work in the asm * code as BITS_PER_TYPE() relies on sizeof(), something not available * in asm. Nethertheless, the concept of fixed width integers is a C * thing which does not apply to assembly code. */ I really believe that it would be a mistake to make the GENMASK_U*() or the BIT_U*() available to assembly. >> David also pointed this in the v3: >> >> https://lore.kernel.org/intel-xe/d42dc197a15649e69d459362849a37f2@xxxxxxxxxxxxxxxx/ >> >> and I agree with his comment. >> >> I explained this in the changelog below the --- cutter, but it is >> probably better to make the explanation more visible. I will add a >> comment in the code to explain this. >> >>>> +#define BIT_U32(b) (BIT_INPUT_CHECK(u32, b) + (u32)BIT(b)) >>>> +#define BIT_U64(b) (BIT_INPUT_CHECK(u64, b) + (u64)BIT_ULL(b)) > Yours sincerely, Vincent Mailhol
