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saagarjha
on Sept 9, 2019
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Popcount CPU instruction
Another quick way that doesn’t rely on builtins is x && !(x & (x - 1)).
tromp
on Sept 9, 2019
[–]
I'd first ask the interviewer whether they're ok with a function is_zero_or_two_power...
mkl
on Sept 9, 2019
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parent
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Isn't that what the "x &&" is for? For x = 0, (x - 1) is 0xffffffff, x & (x-1) is 0, !(x & (x-1)) is 1, and x && !(x & (x-1)) is 0.
tromp
on Sept 9, 2019
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root
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Yes, that's exactly what it's for. The answer I hope for is that they don't care about the case of x==0, so that I can leave out the "x &&" part, leaving the noticeably simpler answer
(x & x-1) == 0
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