On Wed, Aug 7, 2013 at 2:36 PM, Linus Walleij <linus.wall...@linaro.org> 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> > > u16 mask = BITS(4, 12);
nice.I don't have anything against this patch but couldn't understand how this works.So i wrote what i knew as below: #include <stdio.h> #define BIT(nr) (1UL << (nr)) #define BITS(_start, _end) ((BIT(_end) - BIT(_start)) + BIT(_end)) #define BITS_MY(_start, _end) (((BIT(_end-_start+1))-1)<<_start) int main() { printf("%x\n", BITS(4,12)); printf("%x\n", BITS_MY(4,12)); return 0; } > > Yields a mask like this: > > 0001111111110000 > > This patch moves the construct out of the MFD PRCMU driver > and make it available for common use, after noticing in a > review or two that it would be useful for others. > > Cc: Akinobu Mita <m...@miraclelinux.com> > Signed-off-by: Linus Walleij <linus.wall...@linaro.org> > --- > drivers/mfd/dbx500-prcmu-regs.h | 2 -- > include/linux/bitops.h | 1 + > 2 files changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/mfd/dbx500-prcmu-regs.h b/drivers/mfd/dbx500-prcmu-regs.h > index 4f6f0fa..906e75e 100644 > --- a/drivers/mfd/dbx500-prcmu-regs.h > +++ b/drivers/mfd/dbx500-prcmu-regs.h > @@ -13,8 +13,6 @@ > #ifndef __DB8500_PRCMU_REGS_H > #define __DB8500_PRCMU_REGS_H > > -#define BITS(_start, _end) ((BIT(_end) - BIT(_start)) + BIT(_end)) > - > #define PRCM_ACLK_MGT (0x004) > #define PRCM_SVAMMCSPCLK_MGT (0x008) > #define PRCM_SIAMMDSPCLK_MGT (0x00C) > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index a3b6b82..1f9d78b 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -6,6 +6,7 @@ > #define BIT(nr) (1UL << (nr)) > #define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG)) > #define BIT_WORD(nr) ((nr) / BITS_PER_LONG) > +#define BITS(_start, _end) ((BIT(_end) - BIT(_start)) + BIT(_end)) Shouldn't there be compile time check here for checking _end > _start? BUILD_BUG_ON(_end<_start); > #define BITS_PER_BYTE 8 > #define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long)) > #endif > -- > 1.8.1.4 > > -- > 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/ -- 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/