Messages in this thread | | | Subject | Re: [PATCHv3 04/10] linux/kernel: introduce lower_48_bits macro | From | Joe Perches <> | Date | Tue, 22 Feb 2022 10:43:21 -0800 |
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On Tue, 2022-02-22 at 08:56 -0800, Keith Busch wrote: > On Tue, Feb 22, 2022 at 05:50:45PM +0100, Christoph Hellwig wrote: > > On Tue, Feb 22, 2022 at 08:45:53AM -0800, Joe Perches wrote: > > > On Tue, 2022-02-22 at 08:31 -0800, Keith Busch wrote: > > > > +/ * > > > > + * lower_48_bits - return bits 0-47 of a number > > > > + * @n: the number we're accessing > > > > + */ > > > > +#define lower_48_bits(n) ((u64)((n) & 0xffffffffffffull)) > > > > > > why not make this a static inline function? > > > > Agreed. > > Sure, that sounds good to me. I only did it this way to match the > existing local convention, but I personally prefer the inline function > too.
The existing convention is used there to allow the compiler to avoid warnings and unnecessary conversions of a u32 to a u64 when shifting by 32 or more bits.
If it's possible to be used with an architecture dependent typedef like dma_addr_t, then perhaps it's reasonable to do something like:
#define lower_48_bits(val) \ ({ \ typeof(val) high = lower_16_bits(upper_32_bits(val)); \ typeof(val) low = lower_32_bits(val); \ \ (high << 16 << 16) | low; \ })
and have the compiler have the return value be an appropriate type.
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