Re: [PATCH v2 3/9] bitops: Introduce a more generic BITMASK macro

[Joe Perches]

On Wed, 2013-10-16 at 10:56 -0400, Chen, Gong wrote:
> GENMASK is used to create a contiguous bitmask([hi:lo]). It is
> implemented twice in current kernel. One is in EDAC driver, the other
> is in SiS/XGI FB driver. Move it to a more generic place for other
> usage.
[]
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
[]
> @@ -10,6 +10,14 @@
>  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
>  #endif
>  
> +/*
> + * Create a contiguous bitmask starting at bit position @l and ending at
> + * position @h. For example
> + * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.

ull

> + */
> +#define GENMASK(h, l)		(((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
> +#define GENMASK_ULL(h, l)	(((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))


Maybe add a

BUILD_BUG_ON(__builtin_constant_p(l) && __builtin_constant_p(h) && \
	     (h) < (l))

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/