FFS(3)                 FreeBSD Library Functions Manual                 FFS(3)

NAME
     ffs, ffsl, ffsll, fls, flsl, flsll - find first or last bit set in a bit
     string

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <strings.h>

     int
     ffs(int value);

     int
     ffsl(long value);

     int
     ffsll(long long value);

     int
     fls(int value);

     int
     flsl(long value);

     int
     flsll(long long value);

DESCRIPTION
     The ffs(), ffsl() and ffsll() functions find the first (least
     significant) bit set in value and return the index of that bit.

     The fls(), flsl() and flsll() functions find the last (most significant)
     bit set in value and return the index of that bit.

     Bits are numbered starting at 1, the least significant bit.  A return
     value of zero from any of these functions means that the argument was
     zero.

SEE ALSO
     bitstring(3), bitset(9)

HISTORY
     The ffs() function appeared in 4.3BSD.  Its prototype existed previously
     in <string.h> before it was moved to <strings.h> for IEEE Std 1003.1-2001
     ("POSIX.1") compliance.

     The ffsl(), fls() and flsl() functions appeared in FreeBSD 5.3.  The
     ffsll() and flsll() functions appeared in FreeBSD 7.1.

FreeBSD 13.1-RELEASE-p6        October 17, 2015        FreeBSD 13.1-RELEASE-p6