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

[Jason Ekstrand]

On Aug 31, 2015 7:35 AM, "Brian Paul" <brianp at vmware.com> wrote:
>
> 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.

Seems like as good a reason as any any to keep it as-is.

Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>

> -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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