[Mesa-dev] [PATCH 02/14] util: added ffsll() function

[Brian Paul]

On 08/28/2015 07:36 PM, Jason Ekstrand wrote:
>
> On Aug 28, 2015 2:31 PM, "Brian Paul" <brianp at vmware.com
> <mailto:brianp at vmware.com>> wrote:
>  >
>  > v2: fix errant _GNU_SOURCE test, per Matt Turner.
>  > ---
>  >  src/gallium/auxiliary/util/u_math.h | 20 ++++++++++++++++++++
>  >  1 file changed, 20 insertions(+)
>  >
>  > diff --git a/src/gallium/auxiliary/util/u_math.h
> b/src/gallium/auxiliary/util/u_math.h
>  > index 56bd185..c551974 100644
>  > --- a/src/gallium/auxiliary/util/u_math.h
>  > +++ b/src/gallium/auxiliary/util/u_math.h
>  > @@ -389,6 +389,26 @@ unsigned ffs( unsigned u )
>  >  #define ffs __builtin_ffs
>  >  #endif
>  >
>  > +#ifdef HAVE___BUILTIN_FFSLL
>  > +#define ffsll __builtin_ffsll
>  > +#else
>  > +static inline int
>  > +ffsll(long long int val)
>  > +{
>  > +   int bit;
>  > +
>
> Might be better to do
>
> if (val & 0xffffffff)
>      return ffs(val &0xffffffff);
> else
>      return ffs(val >> 32);
>
> That may be a little cheaper.  I don't know if its actually better but
> its one less ffs call (which may cross a library boundary)

I like that too, but I just copied the implementation from imports.c
As was suggested, we can look at consolidating this function and a few 
others into src/util/ later.

-Brian

> --Jason
>
>  > +   bit = ffs((unsigned) (val & 0xffffffff));
>  > +   if (bit != 0)
>  > +      return bit;
>  > +
>  > +   bit = ffs((unsigned) (val >> 32));
>  > +   if (bit != 0)
>  > +      return 32 + bit;
>  > +
>  > +   return 0;
>  > +}
>  > +#endif
>  > +
>  >  #endif /* FFS_DEFINED */
>  >
>  >  /**
>  > --
>  > 1.9.1
>  >
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