On Tue, 2021-11-23 at 09:30 +0100, Geert Uytterhoeven wrote:
We have the upper-case (constant) versions, and already {u32,...}_get_bits()/etc.
These don't work for non-const masks.
Obviously, I know that. Still, just saying.
I'm actually in the opposite camp to you I guess - I much prefer the typed versions (u32_get_bits() and friends) over the FIELD_GET() macros that are more magic.
Mostly though that's because the typed ones also have le32_/be32_/... variants, which are tremendously useful, and so I prefer to use them all across. In fact, I have considered in the past to just remove the upper- case macros entirely but ... no time I guess.
Also, you're using __ffs(), which doesn't work for 64-bit on 32-bit architectures (afaict), so that seems a bit awkward.
That's a valid comment. Can be fixed by using a wrapper macro that checks if typeof(mask) == u64, and uses an __ffs64() version when needed.
You can't really do a typeof()==something, but you can check the size, so yeah, that could be done.
Maybe we can make {u32,...}_get_bits() be doing compile-time only checks if it is indeed a constant? The __field_overflow() usage is already only done if __builtin_constant_p(v), so I guess we can do the same with __bad_mask()?
Are all compilers smart enough to replace the division by field_multiplier(field) by a shift?
In the constant case they are, but you'd have to replace field_multiplier() with the __ffs(), including the size check discussed above. Then it's no longer a constant, and then I'm not so sure it would actually be able to translate it, even if it's "1<<__ffs64(...)". I guess you can check, or just change it to not use the division and multiplication, but shifts/masks instead manually?
IOW - I would much prefer to make the type_get_bits() and friends work for non-constant masks.
In fact, you have e.g. code in drivers/usb/chipidea/udc.c that does things like cpu_to_le32(mul << __ffs(...)) - though in those cases it's actually constant today, so you could already write it as le32_encode_bits(...).
johannes