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mcintyre1994
on Feb 13, 2017
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The Three Ways of XOR
Imagine you only had 4 bit numbers (range 0-15) and you tried to do swap 14, 15 (1110, 1111). You can do that with xor but not with the add method, because you can't store a + b without a wider variable.
jonsen
on Feb 13, 2017
[–]
15 + 15 gives 14
14 - 15 gives 15
mcintyre1994
on Feb 13, 2017
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The way I wrote this was rubbish, edited. I was trying to get at if you have 1110, 1111 then 1110 + 1111 will overflow, but you could xor them.
jonsen
on Feb 13, 2017
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1110 + 1111 = 1101 1101 - 1110 = 1111 1101 - 1111 = 1110
Overflow doesn't matter if you just want to swap.
Sacho
on Feb 13, 2017
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[–]
(Assuming two's complement arithmetic, as amelius pointed out - I don't know if all programming languages and platforms use it)
mcintyre1994
on Feb 13, 2017
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That's a really smart observation I hadn't made, thanks for explaining!
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