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Logcount

Number of ``on'' bits in a two's complement number

(Logcount x) is the number of ``on'' bits in the two's complement representation of x.

(Logcount x) has a guard of (integerp x).

Logcount is a Common Lisp function. See any Common Lisp documentation for more information.

Function: logcount

(defun logcount (x)
  (declare (xargs :guard (integerp x)))
  (cond ((zip x) 0)
        ((< x 0) (logcount (lognot x)))
        ((evenp x)
         (logcount (nonnegative-integer-quotient x 2)))
        (t (1+ (logcount (nonnegative-integer-quotient x 2))))))