man3/ffs.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sat Jul 24 19:39:35 1993 by Rik Faith (faith@cs.unc.edu)
  30 .\"
  31 .\" Modified 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
  32 .\"
  33 .TH FFS 3 2016-10-08 "GNU" "Linux Programmer's Manual"
  34 .SH NAME
  35 ffs, ffsl, ffsll \- find first bit set in a word
  36 .SH SYNOPSIS
  37 .nf
  38 .B #include <strings.h>
  39 .PP
  40 .BI "int ffs(int " i );
  41 .PP
  42 .B #include <string.h>
  43 .PP
  44 .BI "int ffsl(long int " i );
  45 .PP
  46 .BI "int ffsll(long long int " i );
  47 .fi
  48 .PP
  49 .in -4n
  50 Feature Test Macro Requirements for glibc (see
  51 .BR feature_test_macros (7)):
  52 .in
  53 .PP
  54 .PD 0
  55 .ad l
  56 .BR ffs ():
  57 .RS 4
  58 .TP 4
  59 Since glibc 2.12:
  60     _XOPEN_SOURCE >= 700
  61     || ! (_POSIX_C_SOURCE\ >=\ 200809L)
  62     || /* Glibc since 2.19: */ _DEFAULT_SOURCE
  63     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  64 .TP
  65 Before glibc 2.12:
  66 none
  67 .RE
  68 .PP
  69 .BR ffsl (),
  70 .BR ffsll ():
  71 .RS 4
  72 _GNU_SOURCE
  73 .RE
  74 .ad
  75 .PD
  76 .SH DESCRIPTION
  77 The
  78 .BR ffs ()
  79 function returns the position of the first
  80 (least significant) bit set in the word \fIi\fP.
  81 The least significant bit is position 1 and the
  82 most significant position is, for example, 32 or 64.
  83 The functions
  84 .BR ffsll ()
  85 and
  86 .BR ffsl ()
  87 do the same but take
  88 arguments of possibly different size.
  89 .SH RETURN VALUE
  90 These functions return the position of the first bit set,
  91 or 0 if no bits are set in
  92 .IR i .
  93 .SH ATTRIBUTES
  94 For an explanation of the terms used in this section, see
  95 .BR attributes (7).
  96 .TS
  97 allbox;
  98 lbw22 lb lb
  99 l l l.
 100 Interface       Attribute       Value
 101 T{
 102 .BR ffs (),
 103 .BR ffsl (),
 104 .BR ffsll ()
 105 T}      Thread safety   MT-Safe
 106 .TE
 107 .SH CONFORMING TO
 108 .BR ffs ():
 109 POSIX.1-2001, POSIX.1-2008, 4.3BSD.
 110
 111 The
 112 .BR ffsl ()
 113 and
 114 .BR ffsll ()
 115 functions are glibc extensions.
 116 .SH NOTES
 117 BSD systems have a prototype in
 118 .IR <string.h> .
 119 .SH SEE ALSO
 120 .BR memchr (3)