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FFS(3)                   BSD 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)

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.

BSD                           September 29, 2012                           BSD