[ltt-dev] [PATCH 2/4] add a definition for fls() for ARM, taken from the linux kernel

[Mathieu Desnoyers]

* Jason Wessel (jason.wessel at windriver.com) wrote:
> Insert the definition from the linux kernel along with the copyright
> attribution for the fls() operation for ARM.

You could instead use my own clean room reimplementation at:

http://git.efficios.com/?p=babeltrace.git;a=blob;f=tests/test-bitfield.c

(for LGPLv2.1 licensing concerns)

The header of this file states "GPL", but I give you my blessing to relicense
the arch-agnostic fls() implementation as LGPL for UST.

If you don't feel like recoding the arm-specific fls, we can leave it out and
just use the arch-agnostic version for now.

Thanks,

Mathieu

> 
> Signed-off-by: Jason Wessel <jason.wessel at windriver.com>
> ---
>  include/ust/processor.h |   53 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 53 insertions(+), 0 deletions(-)
> 
> diff --git a/include/ust/processor.h b/include/ust/processor.h
> index 01aa290..70e244b 100644
> --- a/include/ust/processor.h
> +++ b/include/ust/processor.h
> @@ -454,6 +454,59 @@ static __inline__ int fls(unsigned int x)
>  struct registers {
>  };
>  
> +/* constant_fls() and fls() were take directly from the linux kernel
> + * sources in 2.6.37 from the file arch/arm/include/asm/bitops.h
> + * which had the following copyright.
> + *
> + * Copyright 1995, Russell King.
> + * Various bits and pieces copyrights include:
> + *  Linus Torvalds (test_bit).
> + * Big endian support: Copyright 2001, Nicolas Pitre
> + *  reworked by rmk.
> + */
> +
> +static inline int constant_fls(int x)
> +{
> +	int r = 32;
> +
> +	if (!x)
> +		return 0;
> +	if (!(x & 0xffff0000u)) {
> +		x <<= 16;
> +		r -= 16;
> +	}
> +	if (!(x & 0xff000000u)) {
> +		x <<= 8;
> +		r -= 8;
> +	}
> +	if (!(x & 0xf0000000u)) {
> +		x <<= 4;
> +		r -= 4;
> +	}
> +	if (!(x & 0xc0000000u)) {
> +		x <<= 2;
> +		r -= 2;
> +	}
> +	if (!(x & 0x80000000u)) {
> +		x <<= 1;
> +		r -= 1;
> +	}
> +	return r;
> +}
> +
> +static __inline__ int fls(unsigned int x)
> +{
> +        int ret;
> +
> +        if (__builtin_constant_p(x))
> +               return constant_fls(x);
> +
> +        asm("clz\t%0, %1" : "=r" (ret) : "r" (x) : "cc");
> +        ret = 32 - ret;
> +        return ret;
> +}
> +/*------- end of source taken from linux kernel headers -------*/
> +
>  #define ARCH_COPY_ADDR(dst) "ldr "dst", =2b\n\t" \
>  "b 55f\n\t" \
>  ".ltorg\n\t" \
> -- 
> 1.6.6.2
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com