-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
peter green
Sent: Saturday, August 16, 2014 7:12 PM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] XC8 Math weirdness?

Josh Koffman wrote:
>     greentemp =3D green * 0x10000;
>     redtemp =3D red * 0x100;
>     bluetemp =3D blue;
>
> The temp variables are all uint32_t, and the input values are all=20
> uint8_t. The goal is to shift the values over so I can then add them=20
> together.
>
> When I execute this code with all of the input values as 0xFF, things=20
> are weird. Green (*0x10000) and Blue (*1) work fine, I end up with
> 0xFF0000 and 0xFF, respectively. However, redtemp ends up with=20
> 0xFFFFFF00, which I can't explain.
>  =20

I think Peter's response to this will get you going. However, it is worth
noting that a shift is likely to be _much_ faster than a multiply (unless o=
f
course the compiler is smart enough to see that this multiply can be
implemented by a shift):

>     greentemp =3D green << 16;
>     redtemp =3D red << 8;
>     bluetemp =3D blue;

~ Bob Ammerman
RAm Systems


--=20
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