Re: [PATCH] mm: nobootmem: avoid type warning about alignment value

[Nicolas Pitre <nico@fluxnic.net>]

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@linaro.org>

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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