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marcoheisig/odd-bits.lisp

Created October 4, 2021 14:12
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Extract the odd bits of an integer.
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odd-bits.lisp
(defun odd-bits (x)
(declare (type (unsigned-byte 32) x))
(setf x (logand (ash x -1) #x55555555))
(setf x (logand (logior (ash x -1) x) #x33333333))
(setf x (logand (logior (ash x -2) x) #x0F0F0F0F))
(setf x (logand (logior (ash x -4) x) #x00FF00FF))
(setf x (logand (logior (ash x -8) x) #x0000FFFF))
x)
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