ARM assembly puzzle

Posted by ivant on Stack Overflow See other posts from Stack Overflow or by ivant
Published on 2010-06-02T18:46:40Z Indexed on 2010/06/02 19:04 UTC
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Filed under:

assembly

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arm

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bit-manipulation

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puzzle

First of all, I'm not sure if solution even exists. I spent more than a couple of hours trying to come up with one, so beware.

The problem:

r1 contains an arbitrary integer, flags are not set according to its value. Set r0 to 1 if r1 is 0x80000000, to 0 otherwise, using only two instructions.

It's easy to do that in 3 instructions (there are many ways), however doing it in 2 seems very hard, and may very well be impossible.

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