Re: Patch to remove undefined C code

From: Abramo Bagnara (abramo@alsa-project.org)
Date: Mon Oct 16 2000 - 13:01:58 EST

Bernd Schmidt wrote:
>
> +
> +#define ___swab64(x) \
> +({ \
> + __u64 __x = (x); \
> + ((__u64)( \
> + (__u64)(((__u64)(__x) & (__u64)0x00000000000000ffULL) << 56) | \
> + (__u64)(((__u64)(__x) & (__u64)0x000000000000ff00ULL) << 40) | \
> + (__u64)(((__u64)(__x) & (__u64)0x0000000000ff0000ULL) << 24) | \
> + (__u64)(((__u64)(__x) & (__u64)0x00000000ff000000ULL) << 8) | \
> + (__u64)(((__u64)(__x) & (__u64)0x000000ff00000000ULL) >> 8) | \
> + (__u64)(((__u64)(__x) & (__u64)0x0000ff0000000000ULL) >> 24) | \
> + (__u64)(((__u64)(__x) & (__u64)0x00ff000000000000ULL) >> 40) | \
> + (__u64)(((__u64)(__x) & (__u64)0xff00000000000000ULL) >> 56) )); \
> +})

Isn't this more efficient?
  n = (x>>32) | (x<<32);
  n = ((n & 0x0000ffff0000ffffLL)<<16) | (n & 0xffff0000ffff0000LL)>>16;
  n = ((n & 0x00ff00ff00ff00ffLL)<<8) | (n & 0xff00ff00ff00ff00LL)>>8;

6 shift
4 and
3 or

instead of

8 shift
8 and
7 or 

-- 
Abramo Bagnara                       mailto:abramo@alsa-project.org

Opera Unica
Via Emilia Interna, 140              Phone: +39.0546.656023
48014 Castel Bolognese (RA) - Italy  Fax:   +39.0546.656023

ALSA project is            http://www.alsa-project.org
sponsored by SuSE Linux    http://www.suse.com

It sounds good!
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