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List:       gmp-devel
Subject:    mpz_remove_ui
From:       kha () treskal ! com (Karl Hasselstrom)
Date:       2003-07-13 19:46:40
Message-ID: 20030713194640.GA14015 () treskal ! com
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On 2003-07-12 11:04:52 -0500, Andrew Friedley (CNS Student Support)
wrote:

> A quick glance at the docs didnt show me anything, but is there a
> quick way to determine if a number is a power of two?

The positive integer x is a power of two iff x & (x-1) == 0. (If x is
indeed a power of two, it will have exactly one set bit; (x-1) will
have that bit unset, so their & will be all zero. If x is not a power
of two, x and (x-1) will have the same most significant set bit, which
will be preserved by the &. Note that this algorithm considers 0 to be
a power of two.)

-- 
Karl Hasselström, kha@treskal.com
      www.treskal.com/kalle

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