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man:ffsl

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 4.16 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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