FFS(3) Linux Programmer's Manual FFS(3)

NAME
       ffs, ffsl, ffsll - find first bit set in a word

SYNOPSIS
       #include 

       int ffs(int i);

       #include 

       int ffsl(long int i);

       int ffsll(long long int i);

   Feature Test Macro Requirements for glibc (see featuretestmacros(7)):

       ffs():
           Since glibc 2.12:
               SVIDSOURCE || BSDSOURCE || POSIXCSOURCE >= 200809L ||
               XOPENSOURCE >= 700 ||
           Before glibc 2.12:
               none
       ffsl(), ffsll():
           GNUSOURCE

DESCRIPTION
       The ffs() function returns the position of the  first  (least  signifi‐
       cant)  bit  set in the word i.  The least significant bit is position 1
       and the most significant position is, for example, 32 or 64.  The func‐
       tions  ffsll()  and  ffsl()  do the same but take arguments of possibly
       different size.

RETURN VALUE
       These functions return the position of the first bit set, or  0  if  no
       bits are set in i.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       ┌───────────────────────┬───────────────┬─────────┐
       │Interface              │ Attribute     │ Value   │
       ├───────────────────────┼───────────────┼─────────┤
       │ffs(), ffsl(), ffsll() │ Thread safety │ MT-Safe │
       └───────────────────────┴───────────────┴─────────┘
CONFORMING TO
       ffs(): 4.3BSD, POSIX.1-2001.

       The ffsl() and ffsll() functions are glibc extensions.

NOTES
       BSD systems have a prototype in .

SEE ALSO
       memchr(3)

COLOPHON
       This page is part of release 3.53 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



GNU                               2010-09-20                            FFS(3)