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SubjectRe: Mark bitrevX() functions as const
David Howells wrote:
> Mark the bit reversal functions as being const as they always return the same
> output for any given input.
>
> Signed-Off-By: David Howells <dhowells@redhat.com>
> ---
>
> include/linux/bitrev.h | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
> index 05e540d..032056b 100644
> --- a/include/linux/bitrev.h
> +++ b/include/linux/bitrev.h
> @@ -5,11 +5,11 @@ #include <linux/types.h>
>
> extern u8 const byte_rev_table[256];
>
> -static inline u8 bitrev8(u8 byte)
> +static inline __attribute__((const)) u8 bitrev8(u8 byte)
> {
> return byte_rev_table[byte];
> }
>
> -extern u32 bitrev32(u32 in);
> +extern __attribute__((const)) u32 bitrev32(u32 in);


Comments:

* overall, I agree with this type of change. several Linux lib
functions could use this sort of annotation.

* I question its usefulness on static [inline] functions, because the
compiler should be able to figure out side effects. have you examined
before-and-after asm to see if the code generation changes for the
inlined area?

* naked __attribute__ is ugly. define something short and memorable in
include/linux/compiler.h.

* another annotation to consider is C99 keyword 'restrict'.

Jeff



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