Re: "undefined behavior"?

Richard Harnden <richard.nospam@gmail.invalid> writes:

On 15/06/2024 19:57, David Brown wrote:

If you want BBX_RGBA to be a typedef for an unsigned 32-bit integer,
write:
     typedef uint32_t BBX_RGBA;
If you want bbx_rgba() to be a function that is typesafe, correct, and
efficient (for any decent compiler), write :
     static inline BBX_RGBA bbx_rgba(uint32_t r, uint32_t g,
             uint32_t b, uint32_t a)
     {
         return (r << 24) | (g << 16) | (b << 8) | a;
     }
 

>
Shouldn't that be ... ?
>
static inline BBX_RGBA bbx_rgba(uint8_t r, uint8_t g,
        uint8_t b, uint8_t a)

Maybe, but the function then needs more care as uint8_t will promote to
int and then r << 24 can be undefined.  One needs

  ((BBX_RGBA)r << 24) | (g << 16) | (b << 8) | a

(assuming that int is never going to be 16 bits or the same issue comes
up with the g << 16 shift).  Given this assumption, I'd just check that
unsigned int is at least 32 bits are use that for BBX_RGBA.

--
Ben.