On Wed, 2013-08-07 at 11:06 +0200, Linus Walleij wrote:
> This macro was invented by Mattias Nilsson for the usecase
> where you want to set a sequence of bits inside a n-bit
> word, while leaving the head and tail of the sequence all
> zeroes. For example:
>
> #include <linux/bitops.h>
BITS is a name that's not easily reused because it's
already in use in a few other places.
There are a few conflicts.
$ git grep -E "^\s*#\s*define\s+\bBITS\b"
arch/arc/include/asm/disasm.h:#define BITS(word, s, e) (((word) >> (s)) &
(~((-2) << ((e) - (s)))))
drivers/input/keyboard/tnetv107x-keypad.c:#define BITS(x)
(BIT(x) - 1)
drivers/mfd/dbx500-prcmu-regs.h:#define BITS(_start, _end) ((BIT(_end) -
BIT(_start)) + BIT(_end))
drivers/net/wireless/iwlwifi/mvm/fw-api-bt-coex.h:#define BITS(nb) (BIT(nb) - 1)
fs/select.c:#define BITS(fds, n) (*FDS_IN(fds, n)|*FDS_OUT(fds,
n)|*FDS_EX(fds, n))
lib/zlib_inflate/inflate.c:#define BITS(n) \
sound/core/oss/rate.c:#define BITS (1<<SHIFT)
> u16 mask = BITS(4, 12);
>
> Yields a mask like this:
>
> 0001111111110000
[]
> diff --git a/drivers/mfd/dbx500-prcmu-regs.h b/drivers/mfd/dbx500-prcmu-regs.h
[]
> @@ -13,8 +13,6 @@
[]
> -#define BITS(_start, _end) ((BIT(_end) - BIT(_start)) + BIT(_end))
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
[]
> @@ -6,6 +6,7 @@
[]
> +#define BITS(_start, _end) ((BIT(_end) - BIT(_start)) + BIT(_end))
Maybe use a statement expression to make sure
the start and end accesses are done only once.
#define BITS(start, end) \
({ \
unsigned long high = BIT(end); \
unsigned long low = BIT(start); \
unsigned long rtn = high + (high - low); \
rtn; \
})
I suggest | instead of + too.
Maybe add a WARN when low > high too.
Maybe make it a function to consolidate
any WARN instead of inline expansion.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
