[Spice-devel] [PATCH spice-common 3/3] SpiceROP: Do not compare to constant

[Frediano Ziglio]

> 
> On Sat, May 07, 2016 at 09:38:07AM -0400, Frediano Ziglio wrote:
> > > 
> > > Silence compile-time warning with clang:
> > >  comparison of constant 16 with expression of type 'SpiceROP' is always
> > >  true [-Wtautological-constant-out-of-range-compare]
> > > ---
> > >  common/pixman_utils.c | 4 ++--
> > >  common/pixman_utils.h | 3 ++-
> > >  2 files changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/common/pixman_utils.c b/common/pixman_utils.c
> > > index 81806c9..5a03ff2 100644
> > > --- a/common/pixman_utils.c
> > > +++ b/common/pixman_utils.c
> > > @@ -311,7 +311,7 @@ void spice_pixman_fill_rect_rop(pixman_image_t *dest,
> > >      spice_assert(height > 0);
> > >      spice_assert(x + width <= pixman_image_get_width(dest));
> > >      spice_assert(y + height <= pixman_image_get_height(dest));
> > > -    spice_assert(rop < 16);
> > > +    spice_assert(rop < SPICE_ROP_END);
> > >  
> > >      if (depth == 8) {
> > >          solid_rop_8_func_t rop_func = solid_rops_8[rop];
> > 
> > What?
> > Honestly I think either we are enabling too much warning or clang is wrong!
> > This is C, not C++, enumerators can be different quite easily so there is
> > no
> > reason to assume that (I would open a bug to clang if this is inside
> > -Wall).
> 
> If you read the C standard literally, enum SpiceROP rop can never have
> 16 as a value, as 16 is not one of the values listed in enum SpiceROP
> definition. Thus, 'rop' being outside of the [0, 15] range is undefined
> behaviour/should never happen. So I would not say clang is wrong. But
> maybe a bit overzealous with the warning ;)
> 
> Christophe
> 

Not that C does too much to enforce it I would say.

enum {
   ENUM_1 = 1,
   ENUM_2 = 2
} my_enum = 5;

Frediano