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1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
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4 | .\" Permission is granted to make and distribute verbatim copies of this |
5 | .\" manual provided the copyright notice and this permission notice are | |
6 | .\" preserved on all copies. | |
7 | .\" | |
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. | |
c13182ef | 12 | .\" |
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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14 | .\" manual page may be incorrect or out-of-date.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 | |
19 | .\" professionally. | |
c13182ef | 20 | .\" |
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21 | .\" Formatted or processed versions of this manual, if unaccompanied by |
22 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 23 | .\" %%%LICENSE_END |
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24 | .\" |
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) | |
c13182ef | 32 | .\" |
4b8c67d9 | 33 | .TH FFS 3 2017-09-15 "GNU" "Linux Programmer's Manual" |
fea681da | 34 | .SH NAME |
81927551 | 35 | ffs, ffsl, ffsll \- find first bit set in a word |
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36 | .SH SYNOPSIS |
37 | .nf | |
38 | .B #include <strings.h> | |
68e4db0a | 39 | .PP |
fea681da | 40 | .BI "int ffs(int " i ); |
dbfe9c70 | 41 | .PP |
fea681da | 42 | .B #include <string.h> |
68e4db0a | 43 | .PP |
fea681da | 44 | .BI "int ffsl(long int " i ); |
68e4db0a | 45 | .PP |
fea681da MK |
46 | .BI "int ffsll(long long int " i ); |
47 | .fi | |
68e4db0a | 48 | .PP |
be403e3d MK |
49 | .in -4n |
50 | Feature Test Macro Requirements for glibc (see | |
51 | .BR feature_test_macros (7)): | |
52 | .in | |
68e4db0a | 53 | .PP |
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54 | .PD 0 |
55 | .ad l | |
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56 | .BR ffs (): |
57 | .RS 4 | |
58 | .TP 4 | |
59 | Since glibc 2.12: | |
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60 | _XOPEN_SOURCE >= 700 |
61 | || ! (_POSIX_C_SOURCE\ >=\ 200809L) | |
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62 | || /* Glibc since 2.19: */ _DEFAULT_SOURCE |
63 | || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE | |
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64 | .TP |
65 | Before glibc 2.12: | |
66 | none | |
67 | .RE | |
68 | .PP | |
69 | .BR ffsl (), | |
70 | .BR ffsll (): | |
2bf696f1 | 71 | .RS 4 |
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72 | .PD 0 |
73 | .TP 4 | |
74 | Since glibc 2.27: | |
75 | .\" glibc commit 68fe16dd327c895c08b9ee443b234c49c13b36e9 | |
76 | _DEFAULT_SOURCE | |
77 | .TP | |
78 | Before glibc 2.27: | |
79 | _GNU_SOURCE | |
80 | .PD | |
2bf696f1 | 81 | .RE |
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82 | .ad |
83 | .PD | |
fea681da | 84 | .SH DESCRIPTION |
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85 | The |
86 | .BR ffs () | |
87 | function returns the position of the first | |
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88 | (least significant) bit set in the word \fIi\fP. |
89 | The least significant bit is position 1 and the | |
75b94dc3 | 90 | most significant position is, for example, 32 or 64. |
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91 | The functions |
92 | .BR ffsll () | |
93 | and | |
94 | .BR ffsl () | |
95 | do the same but take | |
fea681da | 96 | arguments of possibly different size. |
47297adb | 97 | .SH RETURN VALUE |
fea681da | 98 | These functions return the position of the first bit set, |
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99 | or 0 if no bits are set in |
100 | .IR i . | |
7eea6fc3 | 101 | .SH ATTRIBUTES |
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102 | For an explanation of the terms used in this section, see |
103 | .BR attributes (7). | |
104 | .TS | |
105 | allbox; | |
106 | lbw22 lb lb | |
107 | l l l. | |
108 | Interface Attribute Value | |
109 | T{ | |
7eea6fc3 PH |
110 | .BR ffs (), |
111 | .BR ffsl (), | |
7eea6fc3 | 112 | .BR ffsll () |
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113 | T} Thread safety MT-Safe |
114 | .TE | |
47297adb | 115 | .SH CONFORMING TO |
a9c6f658 | 116 | .BR ffs (): |
6d3452a4 | 117 | POSIX.1-2001, POSIX.1-2008, 4.3BSD. |
847e0d88 | 118 | .PP |
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119 | The |
120 | .BR ffsl () | |
121 | and | |
122 | .BR ffsll () | |
36f9a7fe | 123 | functions are glibc extensions. |
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124 | .SH NOTES |
125 | BSD systems have a prototype in | |
126 | .IR <string.h> . | |
47297adb | 127 | .SH SEE ALSO |
0a4f8b7b | 128 | .BR memchr (3) |