NAME

ffs — find first bit set in a bit string

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <strings.h>

int
ffs(int value);

DESCRIPTION

The ffs() function finds the first bit set in value and returns the index of that bit. Bits are numbered starting from 1, starting at the right-most bit. A return value of 0 means that the argument was zero.

SEE ALSO

bitstring(3), ffs32(3), popcount(3)

STANDARDS

The ffs() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

HISTORY

The ffs() function appeared in 4.3BSD. The prototype for it existed previously in the <string.h> header before it was moved to <strings.h> for POSIX compliance.