Simple PASM Question

PropNewbie

Sorry for the simple question but what is the best way to force an arbitrary bit low in a long in PASM

For example if I wanted to toggle the·third bit I would XOR with·0100

mov t1,#1
shl·· t1,#2
xor· target,t1

So how would I set the third·bit low? What I want to do is

mov t1,#1
shl·· t1,#2
not··t1
and· target,t1

but I cannot seem to find a logical·NOT in the PASM command set. Is there a better way - perhaps some trick I don't know about? Can I get a logical NOT somehow? Is that what the NEG commands are for? My understanding is that NEG is just for signed integers.

All advice much appreciated.

Phil Pilgrim (PhiPi)

Use andn.

-Phil

PropNewbie

Ahh... ANDN, of course. So simple...

Thank you.

Timmoore

andn

PropNewbie

Just as a thought, how would one logically NOT in PASM.

Not that I need it now, ANDN will do the job nicely, but it seems the sort of thing I ought to know how to do.

Thanks...

jazzed

xor value, mask

' defined somewhere ...
mask  long -1

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--Steve

Propeller Tools

• Propalyzer: Propeller PC Logic Analyzer
• BMA: An on-chip PASM Debugger
• SPUD: Spin Source Level Debugger

localroger

For logical NOT, you can use XOR. You need a·-1 (all bits on)·sitting around somewhere to XOR your target with, but that's a useful enough constant that you probably have it lying around for some other reason

On edit -- Jazzed beat me to it :-(

Cluso99

I like to use ANDN and OR to specifically turn bit(s) on and off. I use XOR when I just want to flip the bit(s), no matter what state they are in. Makes code more readable and stops any bugs that may creep in.

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