logcount

logcount Function

Syntax:

logcount integer → number-of-on-bits

Arguments and Values:

integer—an integer .

number-of-on-bits—a non-negative integer .

Description:

Computes and returns the number of bits in the two’s-complement binary representation of integer that are ‘on’ or ‘set’. If integer is negative, the 0 bits are counted; otherwise, the 1 bits are counted.

Examples:

(logcount 0) → 0 
(logcount -1) → 0 
(logcount 7) → 3 

(logcount 13) → 3 ;Two’s-complement binary: ...0001101 
(logcount -13) → 2 ;Two’s-complement binary: ...1110011 
(logcount 30) → 4 ;Two’s-complement binary: ...0011110 
(logcount -30) → 4 ;Two’s-complement binary: ...1100010 
(logcount (expt 2 100)) → 1 
(logcount (- (expt 2 100))) → 100 
(logcount (- (1+ (expt 2 100)))) → 1 

Exceptional Situations:

Should signal type-error if its argument is not an integer .

Notes:

Even if the implementation does not represent integers internally in two’s complement binary, logcount behaves as if it did.

The following identity always holds:

(logcount x)

≡ (logcount (- (+ x 1)))

≡ (logcount (lognot x))

Expanded Reference: logcount

tip

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(logcount )