Storm13

Yep, that's me, hiya n_n

Hi, unfortunately I don't exactly have the time these days to take on a student. Like I suggested to you earlier on IRC, I think you should just dive intro trying something especially if you've read the tutorials.

I think most of the common ones are covered in my tutorial. There are some which I haven't touched up on, and you can read about those here:
http://problemkaputt.de/gbatek.htm#thumbinstructionsummary

Scroll down on that site for details.

Consider we have a register r0 = 88XXXXXX where the Xs is the data we want.

Bit shifting:
lsl r0, r0, #0x8
lsr r0, r0, #0x8
-- with two instructions R0 now contains the Xs.

Bit masking:
ldr r1, = (0xFFFFFF)
and r0, r0, r1
-- Now we have R0 with the Xs too.

So to answer your question, yeah, you bit mask it as well. Though it's better to use lsl and lsr in most cases, because they don't require a second register to set up the mask, and lsl with an immediate like this is only takes 1 CPU cycle to execute (the fastest an instruction runs).