Re: [Qemu-devel] [PATCH v3 5/6] bitops: add BITNR macro

["Andreas Färber" <afaerber@suse.de>]

Am 11.11.2013 08:44, schrieb Alexey Kardashevskiy:
> This adds a macro to calculate the highest bit set.

Isn't that already available as ffs / clz GCC builtin with wrapper in
qemu/bitops.h? What's the difference to your macro? CC'ing Paolo.

Andreas

> If used on constant
> values, no code will be generated.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  include/qemu/bitops.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h
> index 304c90c..98ba42a 100644
> --- a/include/qemu/bitops.h
> +++ b/include/qemu/bitops.h
> @@ -23,6 +23,18 @@
>  #define BIT_WORD(nr)		((nr) / BITS_PER_LONG)
>  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
>  
> +#define __BITNR(m, n)  ((m) == ((m) & (1<<(n)))) ? (n) :
> +#define BITNR(m) \
> +    __BITNR((m), 31) __BITNR((m), 30) __BITNR((m), 29) __BITNR((m), 28) \
> +    __BITNR((m), 27) __BITNR((m), 26) __BITNR((m), 25) __BITNR((m), 24) \
> +    __BITNR((m), 23) __BITNR((m), 22) __BITNR((m), 21) __BITNR((m), 20) \
> +    __BITNR((m), 19) __BITNR((m), 18) __BITNR((m), 17) __BITNR((m), 16) \
> +    __BITNR((m), 15) __BITNR((m), 14) __BITNR((m), 13) __BITNR((m), 12) \
> +    __BITNR((m), 11) __BITNR((m), 10) __BITNR((m),  9) __BITNR((m),  8) \
> +    __BITNR((m),  7) __BITNR((m),  6) __BITNR((m),  5) __BITNR((m),  4) \
> +    __BITNR((m),  3) __BITNR((m),  2) __BITNR((m),  1) __BITNR((m),  0) \
> +    -1
> +
>  /**
>   * set_bit - Set a bit in memory
>   * @nr: the bit to set
> 


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