man3/ffs.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" Permission is granted to make and distribute verbatim copies of this
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  12 .\" Since the Linux kernel and libraries are constantly changing, this
  13 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
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  20 .\" Formatted or processed versions of this manual, if unaccompanied by
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  22 .\"
  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified Sat Jul 24 19:39:35 1993 by Rik Faith (faith@cs.unc.edu)
  28 .\"
  29 .\" Modified 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
  30 .\"
  31 .TH FFS 3  2003-08-05 "GNU" "Linux Programmer's Manual"
  32 .SH NAME
  33 ffs \- find first bit set in a word
  34 .SH SYNOPSIS
  35 .nf
  36 .B #include <strings.h>
  37 .sp
  38 .BI "int ffs(int " i );
  39 .sp
  40 .B #define _GNU_SOURCE
  41 .br
  42 .B #include <string.h>
  43 .sp
  44 .BI "int ffsl(long int " i );
  45 .sp
  46 .BI "int ffsll(long long int " i );
  47 .fi
  48 .SH DESCRIPTION
  49 The \fBffs\fP() function returns the position of the first
  50 (least significant) bit set in the word \fIi\fP.
  51 The least significant bit is position 1 and the
  52 most significant position e.g. 32 or 64.
  53 .BR
  54 The functions \fBffsll\fP() and \fBffsl\fP() do the same but take
  55 arguments of possibly different size.
  56 .SH "RETURN VALUE"
  57 These functions return the position of the first bit set,
  58 or 0 if no bits are set in
  59 .IR i .
  60 .SH "CONFORMING TO"
  61 4.3BSD, POSIX.1-2001.
  62 .SH NOTES
  63 BSD systems have a prototype in
  64 .IR <string.h> .
  65 .SH "SEE ALSO"
  66 .BR feature_test_macros (7)