Editing Basic Assembly Programming (section)

===== XOR As a Bit Toggle =====

Remember the level Bit Inverter? We can use a bitwise XOR (written <code>^</code>) to selectively invert bits. The operation <code>m ^ w</code> “toggles” all the bits in <code>w</code> that match up with the ones in <code>m</code>, and leave the rest unchanged. We call <code>w</code> the “word” or “argument” and <code>m</code> the “mask.” Note that these names are specific to this use case and do not apply to all uses of XOR.

So if we want to completely invert a byte, we want to XOR it with a mask which is all ones. To do that, we’ll need to construct the mask. We can’t simply <code>loadi</code>, because our mask has the value <code>255</code> and immediates must be less than 64.

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