Have you considered using a union for that:

union {
  uint32_t rgb_32;
  struct {
    uint8_t red:8;
    uint8_t green:8;
    unit8_t blue:8;
  }col;
}rgb;

This way you can access the 32 bit value with rgb.rgb_32 and, for
example red with rgb.col.red for both reading and writing.

You can still use the shift/multiply methods with rgb.rgb_32 (but you
need to know how the bitfields are ordered by the compiler).

The union means that the variables within it shares the same memory
(rgb_32 and col in this case).

/Ruben

> Hi all,
>=20
> Plugging away at my LED project. I'm currently trying to combine 3
> separate 8 bit values into one 24 bit value (stored in a 32 bit
> variable), and I've come across some weirdness.
>=20
> As part of my function, I've broken things down farther than I usually
> would to help isolate the problem. I now have this code:
>=20
>     greentemp =3D green * 0x10000;
>     redtemp =3D red * 0x100;
>     bluetemp =3D blue;
>=20
> The temp variables are all uint32_t, and the input values are all
> uint8_t. The goal is to shift the values over so I can then add them
> together.
>=20
> When I execute this code with all of the input values as 0xFF, things
> are weird. Green (*0x10000) and Blue (*1) work fine, I end up with
> 0xFF0000 and 0xFF, respectively. However, redtemp ends up with
> 0xFFFFFF00, which I can't explain.
>=20
> Changing the red multiplier to 0x10000 (just as a test) works.
> Changing it to 0x1 works as well. But...0x100 doesn't.
>=20
> I know I'm probably missing something simple here, but I can't seem to
> figure it out.
>=20
> Help!
>=20
> Josh
> --=20
> A common mistake that people make when trying to design something
> completely foolproof is to underestimate the ingenuity of complete
> fools.
>         -Douglas Adams
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>=20
>=20
> -----
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>=20

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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