POPCOUNT(3) Library Functions Manual POPCOUNT(3)

popcount, popcountl, popcountll, popcount32, popcount64
count number of bits set in a bit string

Standard C Library (libc, -lc)

#include <strings.h>

unsigned int
popcount(unsigned int value);

unsigned int
popcountl(unsigned long value);

unsigned int
popcountll(unsigned long long value);

#include <stdint.h>

unsigned int
popcount32(uint32_t value);

unsigned int
popcount64(uint64_t value);

The popcount functions return the number of bits set in value.

ffs(3)

The popcount(), popcountl(), popcountll(), popcount32(), and popcount64() functions appeared in NetBSD 6.0.
August 22, 2011 NetBSD 9.2