ternary vs double exclamation

[Vinícius Tinti]

Hi,

I was looking the kernel source code and there are a lot of places in
which either "(expression) ? 1 : 0" or "(expression) ? 0 : 1" appear.
As fair as I can tell both can be replaced by "!!expression" and
"!expression".

Moreover there it seems that using "!!" does not add a "nopl"
instruction at the end of the call. Does anybody knows why?

Anyway. Wouldn't be nice if kernel provides something like
"boolean(x)" macro and  "inv_boolean(x)" to do this operations?

#ifdef MOD_IF
int mod_if(int x) {
    return (x == 0) ? 0 : 1;
}
#endif

#ifdef MOD_X
int mod_x(int x) {
    return !!x;
}
#endif

0000000000000000 <mod_if>:
   0:   31 c0                   xor    %eax,%eax
   2:   85 ff                   test   %edi,%edi
   4:   0f 95 c0                setne  %al
   7:   c3                      retq
   8:   0f 1f 84 00 00 00 00    nopl   0x0(%rax,%rax,1)
   f:   00

0000000000000010 <mod_x>:
  10:   31 c0                   xor    %eax,%eax
  12:   85 ff                   test   %edi,%edi
  14:   0f 95 c0                setne  %al
  17:   c3                      retq


Regards,
Vinícius

-- 
Simplicity is the ultimate sophistication