1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
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8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
29 .\" Modified Sat Jul 24 19:39:35 1993 by Rik Faith (faith@cs.unc.edu)
31 .\" Modified 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
33 .TH FFS 3 2014-04-14 "GNU" "Linux Programmer's Manual"
35 ffs, ffsl, ffsll \- find first bit set in a word
38 .B #include <strings.h>
40 .BI "int ffs(int " i );
42 .B #include <string.h>
44 .BI "int ffsl(long int " i );
46 .BI "int ffsll(long long int " i );
50 Feature Test Macro Requirements for glibc (see
51 .BR feature_test_macros (7)):
60 _SVID_SOURCE || _BSD_SOURCE ||
61 _POSIX_C_SOURCE\ >=\ 200809L || _XOPEN_SOURCE\ >=\ 700 ||
77 function returns the position of the first
78 (least significant) bit set in the word \fIi\fP.
79 The least significant bit is position 1 and the
80 most significant position is, for example, 32 or 64.
86 arguments of possibly different size.
88 These functions return the position of the first bit set,
89 or 0 if no bits are set in
92 .SS Multithreading (see pthreads(7))
98 functions are thread-safe.
101 4.3BSD, POSIX.1-2001.
107 functions are glibc extensions.
109 BSD systems have a prototype in