On Sun, 12 Jan 2014, Russell King - ARM Linux wrote:
> This patch makes their types match exactly with x86's definitions of
> the same, which is the basic problem: on ARM, they all took "int" values
> and returned "int"s, which leads to min() in nobootmem.c complaining.
>
> arch/arm/include/asm/bitops.h | 54 +++++++++++++++++++++++++++++++++++--------
> 1 file changed, 44 insertions(+), 10 deletions(-)
For the record:
Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
The reason why macros were used at the time this was originally written
is because gcc used to have issues forwarding the constant nature of a
variable down multiple levels of inline functions and
__builtin_constant_p() always returned false. But that was quite a long
time ago.
> diff --git a/arch/arm/include/asm/bitops.h b/arch/arm/include/asm/bitops.h
> index e691ec91e4d3..b2e298a90d76 100644
> --- a/arch/arm/include/asm/bitops.h
> +++ b/arch/arm/include/asm/bitops.h
> @@ -254,25 +254,59 @@ static inline int constant_fls(int x)
> }
>
> /*
> - * On ARMv5 and above those functions can be implemented around
> - * the clz instruction for much better code efficiency.
> + * On ARMv5 and above those functions can be implemented around the
> + * clz instruction for much better code efficiency. __clz returns
> + * the number of leading zeros, zero input will return 32, and
> + * 0x80000000 will return 0.
> */
> +static inline unsigned int __clz(unsigned int x)
> +{
> + unsigned int ret;
> +
> + asm("clz\t%0, %1" : "=r" (ret) : "r" (x));
>
> + return ret;
> +}
> +
> +/*
> + * fls() returns zero if the input is zero, otherwise returns the bit
> + * position of the last set bit, where the LSB is 1 and MSB is 32.
> + */
> static inline int fls(int x)
> {
> - int ret;
> -
> if (__builtin_constant_p(x))
> return constant_fls(x);
>
> - asm("clz\t%0, %1" : "=r" (ret) : "r" (x));
> - ret = 32 - ret;
> - return ret;
> + return 32 - __clz(x);
> +}
> +
> +/*
> + * __fls() returns the bit position of the last bit set, where the
> + * LSB is 0 and MSB is 31. Zero input is undefined.
> + */
> +static inline unsigned long __fls(unsigned long x)
> +{
> + return fls(x) - 1;
> +}
> +
> +/*
> + * ffs() returns zero if the input was zero, otherwise returns the bit
> + * position of the first set bit, where the LSB is 1 and MSB is 32.
> + */
> +static inline int ffs(int x)
> +{
> + return fls(x & -x);
> +}
> +
> +/*
> + * __ffs() returns the bit position of the first bit set, where the
> + * LSB is 0 and MSB is 31. Zero input is undefined.
> + */
> +static inline unsigned long __ffs(unsigned long x)
> +{
> + return ffs(x) - 1;
> }
>
> -#define __fls(x) (fls(x) - 1)
> -#define ffs(x) ({ unsigned long __t = (x); fls(__t & -__t); })
> -#define __ffs(x) (ffs(x) - 1)
> #define ffz(x) __ffs( ~(x) )
>
> #endif
>
>
> --
> FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up. Estimation
> in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
> Estimate before purchase was "up to 13.2Mbit".
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