Counting bits set in a 32 bit value

[Bruno Jesus]

Hi all, after some manual testing I noticed that the joystick
structure member dwButtonNumber is not the last button pressed but
instead the count of pressed buttons. There is a bit field of buttons
set in the structure member dwButton, to fix the number in
dwButtonNumber I guess the easiest way is to count the bits set.

I think that keeping a counter with ++/-- operations could lead to out
of sync situations if the joystick is not polled fast enough.

Is there any precedent need for this in wine? Is there an accepted
solution for it? Internet searching shows different ways like bit
counting with shift, using cpu instructions or internal compiler
functions.

Best wishes,
Bruno

[Henri Verbeet]

On 23 March 2015 at 15:47, Bruno Jesus  wrote:
> Is there any precedent need for this in wine? Is there an accepted
> solution for it? Internet searching shows different ways like bit
> counting with shift, using cpu instructions or internal compiler
> functions.

We have e.g. count_bits() in dlls/wined3d/util.c, but you'll probably
want to use __builtin_popcount() on gcc.