On Sun, Oct 01, 2017 at 06:10:35PM +0200, Michael Niedermayer wrote:
> 32% faster loop
>
> Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
> ---
> libavcodec/dvbsubdec.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/libavcodec/dvbsubdec.c b/libavcodec/dvbsubdec.c
> index b683109643..6a40f2376f 100644
> --- a/libavcodec/dvbsubdec.c
> +++ b/libavcodec/dvbsubdec.c
> @@ -653,8 +653,9 @@ static void compute_default_clut(AVSubtitleRect *rect,
> int w, int h)
> uint8_t list_inv[256];
> int counttab[256] = {0};
> int count, i, x, y;
> + ptrdiff_t ls = rect->linesize[0];
You use this variable in 3 places where the length doesn't matter; please
use a longer name (maybe "lsize", "stride", or even "linesize").
>
> -#define V(x,y) rect->data[0][(x) + (y)*rect->linesize[0]]
> +#define V(x,y) rect->data[0][(x) + (y)*ls]
> for (y = 0; y<h; y++) {
> for (x = 0; x<w; x++) {
> int v = V(x,y) + 1;
> @@ -665,7 +666,7 @@ static void compute_default_clut(AVSubtitleRect *rect,
> int w, int h)
> counttab[v-1] += !!((v!=vl) + (v!=vr) + (v!=vt) + (v!=vb));
> }
> }
> -#define L(x,y) list[ rect->data[0][(x) + (y)*rect->linesize[0]] ]
> +#define L(x,y) list[ d[(x) + (y)*ls] ]
since you modify this line, feel free to drop the extra spacing
after and before the [].
>
> for (i = 0; i<256; i++) {
> int scoretab[256] = {0};
> @@ -673,12 +674,13 @@ static void compute_default_clut(AVSubtitleRect *rect,
> int w, int h)
> int bestv = 0;
> for (y = 0; y<h; y++) {
> for (x = 0; x<w; x++) {
> - int v = rect->data[0][x + y*rect->linesize[0]];
> + uint8_t *d = &rect->data[0][x + y*ls];
> + int v = *d;
> int l_m = list[v];
> - int l_l = x ? L(x-1, y) : 1;
> - int l_r = x+1<w ? L(x+1, y) : 1;
> - int l_t = y ? L(x, y-1) : 1;
> - int l_b = y+1<h ? L(x, y+1) : 1;
> + int l_l = x ? L(-1, 0) : 1;
> + int l_r = x+1<w ? L(+1, 0) : 1;
> + int l_t = y ? L(0, -1) : 1;
> + int l_b = y+1<h ? L(0, +1) : 1;
I'd be more comfortable with:
int l_l = x ? L(-1, 0) : 1;
int l_r = x+1<w ? L( 1, 0) : 1;
int l_t = y ? L( 0,-1) : 1;
int l_b = y+1<h ? L( 0, 1) : 1;
I feel like at some point in the future compilers will complain about
these "(+3)*x"
Should be fine otherwise
--
Clément B.
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