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+'\" t
+.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" References consulted:
+.\"     Linux libc source code
+.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
+.\"     386BSD man pages
+.\" Modified Sat Jul 24 19:39:35 1993 by Rik Faith (faith@cs.unc.edu)
+.\"
+.\" Modified 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
+.\"
+.TH ffs 3 (date) "Linux man-pages (unreleased)"
+.SH NAME
+ffs, ffsl, ffsll \- find first bit set in a word
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <strings.h>
+.P
+.BI "int ffs(int " i );
+.BI "int ffsl(long " i );
+.BI "int ffsll(long long " i );
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR ffs ():
+.nf
+    Since glibc 2.12:
+        _XOPEN_SOURCE >= 700
+            || ! (_POSIX_C_SOURCE >= 200809L)
+            || /* glibc >= 2.19: */ _DEFAULT_SOURCE
+            || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+    Before glibc 2.12:
+        none
+.fi
+.P
+.BR ffsl (),
+.BR ffsll ():
+.nf
+    Since glibc 2.27:
+.\" glibc commit 68fe16dd327c895c08b9ee443b234c49c13b36e9
+        _DEFAULT_SOURCE
+    Before glibc 2.27:
+        _GNU_SOURCE
+.fi
+.SH DESCRIPTION
+The
+.BR ffs ()
+function returns the position of the first
+(least significant) bit set in the word \fIi\fP.
+The least significant bit is position 1 and the
+most significant position is, for example, 32 or 64.
+The functions
+.BR ffsll ()
+and
+.BR ffsl ()
+do the same but take
+arguments of possibly different size.
+.SH RETURN VALUE
+These functions return the position of the first bit set,
+or 0 if no bits are set in
+.IR i .
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR ffs (),
+.BR ffsl (),
+.BR ffsll ()
+T}	Thread safety	MT-Safe
+.TE
+.SH STANDARDS
+.TP
+.BR ffs ()
+POSIX.1-2001, POSIX.1-2008, 4.3BSD.
+.TP
+.BR ffsl ()
+.TQ
+.BR ffsll ()
+GNU.
+.SH SEE ALSO
+.BR memchr (3)