bitwise-bit-count

[procedure] bitwise-bit-count e1

R6RS: If e1 is positive, returns the number of '1' bits in it. Otherwise, the result will be:

(bitwise-not (bitwise-bit-count (bitwise-not e1)))

The logcount procedure in SLIB etc. also counts the number of '1' bits for the positive exact integer argument; but it works differently if the argument is negative (logcount returns the number of '0' bits in such case).