[IPOL discuss] RGB->gray conversion and speed comparison

[Miguel Colom]

> Otherwise, I have no doubts about its portability.  There is no
> dependency on sign representation or endianness in Nicolas' solution.
> Bitwise operations are defined in the C standard just like the
> arithmetic operations.

I think the problem could arise in this bit-wise AND:
"& (1 << 14)"

Not all architectures will store the 14th bit in the same position inside
a integer.