Re: [PATCH 10/71] core: helper funtion for initializing rects with zero

On Mon, Apr 17, 2017 at 06:56:49PM +0200, Enrico Weigelt, metux IT consult wrote:
> In some places we zero-out rects field-by-field.
> 
> On one hand we should encapsulate that in a helper, to make the source
> a bit easier to read, and to have it all in one place, in case of
> possible later changes.

Unless there are other places where _cairo_zero_rectangle_init() can be
used (I couldn't find any), just set extents to {0} directly.

If we had a convention for init routines that zero out structs it might
be worth it, but adding a routine for creating a degenerate rect seems
unnecessary.
 
> OTOH, use static zero initializer instead of explicit field-by-field,
> to allow the compiler to use vector ops and so save a few cycles
> on certain cpu archs.

If this is a measurable optimization, there could be additional spots in
the code where this approach could be beneficial, although I'm only
finding places where structs are *mostly* zero with a few members set to
other values (e.g. cairo_matrix_init).

> Signed-off-by: Enrico Weigelt, metux IT consult <[email protected]>
> ---
>  src/cairo-path-bounds.c | 3 +--
>  src/cairoint.h          | 6 ++++++
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/src/cairo-path-bounds.c b/src/cairo-path-bounds.c
> index 624b3cb4d..6dcf90cf1 100644
> --- a/src/cairo-path-bounds.c
> +++ b/src/cairo-path-bounds.c
> @@ -144,8 +144,7 @@ _cairo_path_fixed_fill_extents (const cairo_path_fixed_t	*path,
>  	path->extents.p1.y < path->extents.p2.y) {
>  	_cairo_box_round_to_rectangle (&path->extents, extents);
>      } else {
> -	extents->x = extents->y = 0;
> -	extents->width = extents->height = 0;
> +	_cairo_zero_rectangle_init (extents);
>      }
>  }
>  
> diff --git a/src/cairoint.h b/src/cairoint.h
> index 493d46103..d83481632 100644
> --- a/src/cairoint.h
> +++ b/src/cairoint.h
> @@ -333,6 +333,12 @@ _cairo_unbounded_rectangle_init (cairo_rectangle_int_t *rect)
>      *rect = _cairo_unbounded_rectangle;
>  }
>  
> +static inline void
> +_cairo_zero_rectangle_init (cairo_rectangle_int_t *rect)
> +{
> +    *rect = (cairo_rectangle_int_t){ 0 };
> +}
> +
>  cairo_private_no_warn cairo_bool_t
>  _cairo_rectangle_intersect (cairo_rectangle_int_t *dst,
>  			    const cairo_rectangle_int_t *src);
> -- 
> 2.11.0.rc0.7.gbe5a750
> 
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