[sldev] [patch] OpenJPEG fix_mul() optimization

[alissa_sabre at yahoo.co.jp]

> Attached is a simple change that gives up to 10% extra performance in 
> DWT time.

Hmm.  If this fix_mul() is so important, why don't you make it as
follows?  It's simpler, does same thing, and should be slightly faster
in general...

static INLINE int fix_mul(int a, int b) {
    return (int) (((int64) a * (int64) b + 4096) >> 13);
}

> --- libopenjpeg/fix.h    (revision 369)
> +++ libopenjpeg/fix.h    (working copy)
> @@ -54,8 +54,9 @@
>  @return Returns a * b
>  */
>  static INLINE int fix_mul(int a, int b) {
> -    int64 temp = (int64) a * (int64) b >> 12;
> -    return (int) ((temp >> 1) + (temp & 1)) ;
> +    int64 temp = (int64) a * (int64) b ;
> +    temp += temp & 4096;
> +    return (int) (temp >> 13) ;
>  }

 

 
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