How to invert all bits in ASM (NOT instruction)

peterz

Is there an equivalent to NOT instruction in ASM ?
I want to invert all bits in a variable located in an ASM block.

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Graham Stabler

You could use ANDN and use your value for both arguments?

Or XOR with 111111.......

Graham

p.s. This is really handy: http://forums.parallax.com/forums/default.aspx?f=25&m=157555

peterz

But I want to invert a full 32bits value and the ASM complaints: constant cannot exceed $1FF

For example I cannot do:

xor t1,#$FFFFFFFF

Remy Blank

peterz said...
But I want to invert a full 32bits value and the ASM complaints: constant cannot exceed $1FF

For example I cannot do:

xor t1,#$FFFFFFFF

You'll have to store your $ffffffff constant in a long:

xor   t1, allOne
...
allOne   long $ffffffff

-- Remy

Jasper_M

Graham Stabler said...
You could use ANDN and use your value for both arguments?

That wouldn't actually work - it would and the ORIGINAL value with it's inverted value, resulting in zero. eg.

if you'd andn %1001 with itself, the result would be %1001 & %0110 = %0000. Therefore XORing with $FF_FF_FF_FF seems to be the only real option.