Bug#369917: xserver-xorg-input-mouse: Gets number of buttons wrong, even if Option "Buttons" specified

[Drew Parsons <dparsons@debian.org>]

> I find that the server is getting the number of buttons wrong (too
> high).
> 
> (**) Configured Mouse: ZAxisMapping: buttons 9 and 10
> (**) Configured Mouse: Buttons: 14

For reference this button count appears to be coming from mouse.c l.706,

    /* get maximum of mapped buttons */
    for (i = pMse->buttons-1; i >= 0; i--) {
        int f = ffs (pMse->buttonMap[i]);
        if (f > pMse->buttons)
            pMse->buttons = f;
    }


That is, the original value is being reset to the value of 
ffs(pMse->buttonMap[i]), where this is larger.  The larger number
appears to be ("actual" number)+4.  At a guess, the extra 4 buttons
correspond to the X- and Y-axes, with the normal mouse wheel occupying
the Z-axis.

ffs is defined or referred to in /usr/include/xorg/compiler.h
and ../xf86_libc.h (xserver-xorg-dev).  A low level definition is found
in /usr/include/asm-generic/bitops/ffs.h, "find first bit set"

I suspect this is not actually a bug.

Drew