Re: [FFmpeg-devel] [PATCH] avcodec/xbmenc: Avoid snprintf() for data->hex conversion

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> Use a small LUT instead. Improves performance.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/xbmenc.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/libavcodec/xbmenc.c b/libavcodec/xbmenc.c
> index cd8b73afa3..5231d4691d 100644
> --- a/libavcodec/xbmenc.c
> +++ b/libavcodec/xbmenc.c
> @@ -20,11 +20,9 @@
>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>   */
>  
> -#include "libavutil/reverse.h"
>  #include "avcodec.h"
>  #include "codec_internal.h"
>  #include "encode.h"
> -#include "mathops.h"
>  
>  #define ANSI_MIN_READLINE 509
>  
> @@ -57,14 +55,25 @@ static int xbm_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
>      buf += snprintf(buf, 39, "static unsigned char image_bits[] = {\n");
>      for (i = 0, l = lineout; i < avctx->height; i++) {
>          for (j = 0; j < linesize; j++) {
> -            buf += snprintf(buf, 6, " 0x%02X", ff_reverse[*ptr++]);
> +            // 0..15 bitreversed as chars
> +            static const char lut[] = {
> +                '0', '8', '4', 'C', '2', 'A', '6', 'E',
> +                '1', '9', '5', 'D', '3', 'B', '7', 'F'
> +            };
> +            buf[0] = ' ';
> +            buf[1] = '0';
> +            buf[2] = 'x';
> +            buf[3] = lut[*ptr & 0xF];
> +            buf[4] = lut[*ptr >> 4];
> +            buf += 5;
> +            ptr++;
>              if (--commas <= 0) {
> -                buf += snprintf(buf, 2, "\n");
> +                *buf++ = '\n';
>                  break;
>              }
> -            buf += snprintf(buf, 2, ",");
> +            *buf++ = ',';
>              if (--l <= 0) {
> -                buf += snprintf(buf, 2, "\n");
> +                *buf++ = '\n';
>                  l = lineout;
>              }
>          }

Will apply.

- Andreas

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