[Spice-devel] [PATCH spice-common 2/3] lz: Optimise SAME_PIXEL for RGB16

[Jonathon Jongsma]

On Wed, 2018-05-09 at 14:10 +0100, Frediano Ziglio wrote:
> Do not extract all components and compare one by one, can be easily
> compared together.

Do you have some data about how performance compares between the two
implementations? The new implementation clearly looks more efficient,
but the code is not as straightforward to understand at a glance (at
least for me). If it's called a lot, it clearly makes sense to optimize
the implementation, but if not, I'm a bit ambivalent about the change.

Jonathon


> 
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> ---
>  common/lz_compress_tmpl.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/common/lz_compress_tmpl.c b/common/lz_compress_tmpl.c
> index 69e69a6..b778e9d 100644
> --- a/common/lz_compress_tmpl.c
> +++ b/common/lz_compress_tmpl.c
> @@ -105,9 +105,7 @@
>  #ifdef LZ_RGB16
>  #define PIXEL rgb16_pixel_t
>  #define FNAME(name) lz_rgb16_##name
> -#define GET_r(pix) (((pix) >> 10) & 0x1f)
> -#define GET_g(pix) (((pix) >> 5) & 0x1f)
> -#define GET_b(pix) ((pix) & 0x1f)
> +#define SAME_PIXEL(p1, p2) ((((p1)^(p2)) & 0x7fffu) == 0)
>  #define ENCODE_PIXEL(e, pix) {encode(e, (pix) >> 8); encode(e, (pix)
> & 0xff);}
>  
>  #define HASH_FUNC(v, p) {                 \
> @@ -153,7 +151,7 @@
>      }
>  #endif
>  
> -#if defined(LZ_RGB16) || defined(LZ_RGB24) || defined(LZ_RGB32)
> +#if defined(LZ_RGB24) || defined(LZ_RGB32)
>  #define SAME_PIXEL(p1, p2) (GET_r(p1) == GET_r(p2) && GET_g(p1) ==
> GET_g(p2) && \
>                              GET_b(p1) == GET_b(p2))
>