Re: [FFmpeg-devel] [PATCH] avcodec/xpmdec: Use LUT for hex char->number conversion

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

Andreas Rheinhardt:
> Speeds up decoding and also reduces binary size.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/xpmdec.c | 25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/libavcodec/xpmdec.c b/libavcodec/xpmdec.c
> index 5bc02378c8..804cf8568d 100644
> --- a/libavcodec/xpmdec.c
> +++ b/libavcodec/xpmdec.c
> @@ -193,15 +193,22 @@ static const ColorEntry color_table[] = {
>  
>  static unsigned hex_char_to_number(uint8_t x)
>  {
> -    if (x >= 'a' && x <= 'f')
> -        x -= 'a' - 10;
> -    else if (x >= 'A' && x <= 'F')
> -        x -= 'A' - 10;
> -    else if (x >= '0' && x <= '9')
> -        x -= '0';
> -    else
> -        x = 0;
> -    return x;
> +#define TIMES256(idx) \
> +TIMES64(4 * (idx)) TIMES64(4 * (idx) + 1) TIMES64(4 * (idx) + 2) TIMES64(4 * (idx) + 3)
> +#define TIMES64(idx) \
> +TIMES16(4 * (idx)) TIMES16(4 * (idx) + 1) TIMES16(4 * (idx) + 2) TIMES16(4 * (idx) + 3)
> +#define TIMES16(idx) \
> +TIMES4(4 * (idx)) TIMES4(4 * (idx) + 1) TIMES4(4 * (idx) + 2) TIMES4(4 * (idx) + 3)
> +#define TIMES4(idx) \
> +ENTRY(4 * (idx)) ENTRY(4 * (idx) + 1) ENTRY(4 * (idx) + 2) ENTRY(4 * (idx) + 3)
> +#define ENTRY(x) [x] = ((x) >= 'a' && (x) <= 'f') ? (x) - ('a' - 10) : \
> +                       ((x) >= 'A' && (x) <= 'F') ? (x) - ('A' - 10) : \
> +                       ((x) >= '0' && (x) <= '9') ? (x) - '0' : 0,
> +
> +    static const uint8_t lut[] = {
> +        TIMES256(0)
> +    };
> +    return lut[x];
>  }
>  
>  /*

Will apply.

- Andreas

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