Re: [Qemu-devel] [RFC][PATCH 4/9] buffer_is_zero: use vector optimizations if possible

[Eric Blake <eblake@redhat.com>]

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On 03/12/2013 09:50 AM, Peter Lieven wrote:
> performance gain on SSE2 is approx. 20-25%. altivec
> is not tested. performance for unsigned long arithmetic
> is unchanged.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  util/cutils.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/util/cutils.c b/util/cutils.c
> index a09d8e8..23f0cd6 100644
> --- a/util/cutils.c
> +++ b/util/cutils.c
> @@ -186,6 +186,11 @@ bool buffer_is_zero(const void *buf, size_t len)
>       * latency.
>       */
> 
> +    if (((uintptr_t) buf) % sizeof(VECTYPE) == 0
> +          && len % 8*sizeof(VECTYPE) == 0) {

Space around binary operators.  Use CHAR_BITS instead of a magic number
8.  Also, did you mean:

len % (CHAR_BITS * sizeof(VECTYPE))

instead of what you wrote as '(len % 8) * sizeof(VECTYPE)'?

> +        return buffer_find_nonzero_offset(buf, len)==len;
> +    }
> +
>      size_t i;
>      long d0, d1, d2, d3;
>      const long * const data = buf;

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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