NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

The Linux Programming Interface

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

NAME         top

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

SYNOPSIS         top

       #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:
               _SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 200809L ||
               _XOPEN_SOURCE >= 700 ||
           Before glibc 2.12:
               none
       ffsl(), ffsll():
           _GNU_SOURCE

DESCRIPTION         top

       The ffs() function returns the position of the first (least significant) 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 functions ffsll() and
       ffsl() do the same but take arguments of possibly different size.

RETURN VALUE         top

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

CONFORMING TO         top

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

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

NOTES         top

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

SEE ALSO         top

       memchr(3)

COLOPHON         top

       This page is part of release 3.32 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)

HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface