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ffs(3)

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



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

SYNOPSIS
       #include <strings.h>

       int ffs(int i);

       #include <string.h>

       int ffsl(long int i);

       int ffsll(long long int i);

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

       ffs():
           Since glibc 2.12:
                   _XOPEN_SOURCE >= 700
                   || ! (_POSIX_C_SOURCE >= 200809L)
                   || /* Glibc since 2.19: */ _DEFAULT_SOURCE
                   || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
               _SVID_SOURCE
           Before glibc 2.12:
               none
       ffsl(), ffsll():
           Since glibc 2.27:
                   _DEFAULT_SOURCE
           Before glibc 2.27:
                   _GNU_SOURCE

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).

       allbox; lbw22 lb lb l l l.  Interface Attribute Value T{ ffs(), ffsl(),
       ffsll() T}   Thread safety  MT-Safe

CONFORMING TO
       ffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.

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

NOTES
       BSD systems have a prototype in <string.h>.

SEE ALSO
       memchr(3)

COLOPHON
       This  page  is  part of release 5.02 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.



GNU                               2017-09-15                            FFS(3)
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