stdarg.3: SEE ALSO: add vprintf(3), vscanf(3), vsyslog(3)

[thirdparty/man-pages.git] / man3 / ffs.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" preserved on all copies.
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.\" manual under the conditions for verbatim copying, provided that the
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.\" 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 2017-09-15 "GNU" "Linux Programmer's Manual"
.SH NAME
ffs, ffsl, ffsll \- find first bit set in a word
.SH SYNOPSIS
.nf
.B #include <strings.h>
.PP
.BI "int ffs(int " i );
.PP
.B #include <string.h>
.PP
.BI "int ffsl(long int " i );
.PP
.BI "int ffsll(long long int " i );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.PD 0
.ad l
.BR ffs ():
.RS 4
.TP 4
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
.TP
Before glibc 2.12:
none
.RE
.PP
.BR ffsl (),
.BR ffsll ():
.RS 4
.PD 0
.TP 4
Since glibc 2.27:
.\" glibc commit 68fe16dd327c895c08b9ee443b234c49c13b36e9
    _DEFAULT_SOURCE
.TP
Before glibc 2.27:
    _GNU_SOURCE
.PD
.RE
.ad
.PD
.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;
lbw22 lb lb
l l l.
Interface	Attribute	Value
T{
.BR ffs (),
.BR ffsl (),
.BR ffsll ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
.BR ffs ():
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
.PP
The
.BR ffsl ()
and
.BR ffsll ()
functions are glibc extensions.
.SH NOTES
BSD systems have a prototype in
.IR <string.h> .
.SH SEE ALSO
.BR memchr (3)