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1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
5fbde956 | 3 | .\" SPDX-License-Identifier: Linux-man-pages-copyleft |
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4 | .\" |
5 | .\" References consulted: | |
6 | .\" Linux libc source code | |
7 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
8 | .\" 386BSD man pages | |
9 | .\" Modified Sat Jul 24 19:39:35 1993 by Rik Faith (faith@cs.unc.edu) | |
10 | .\" | |
11 | .\" Modified 2003 Walter Harms (walter.harms@informatik.uni-oldenburg.de) | |
c13182ef | 12 | .\" |
45186a5d | 13 | .TH FFS 3 2021-03-22 "Linux man-pages (unreleased)" |
fea681da | 14 | .SH NAME |
81927551 | 15 | ffs, ffsl, ffsll \- find first bit set in a word |
afa8db94 AC |
16 | .SH LIBRARY |
17 | Standard C library | |
18 | .RI ( libc ", " \-lc ) | |
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19 | .SH SYNOPSIS |
20 | .nf | |
21 | .B #include <strings.h> | |
68e4db0a | 22 | .PP |
fea681da | 23 | .BI "int ffs(int " i ); |
dbfe9c70 | 24 | .PP |
fea681da | 25 | .B #include <string.h> |
68e4db0a | 26 | .PP |
ae85f653 | 27 | .BI "int ffsl(long " i ); |
ae85f653 | 28 | .BI "int ffsll(long long " i ); |
fea681da | 29 | .fi |
68e4db0a | 30 | .PP |
d39ad78f | 31 | .RS -4 |
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32 | Feature Test Macro Requirements for glibc (see |
33 | .BR feature_test_macros (7)): | |
d39ad78f | 34 | .RE |
68e4db0a | 35 | .PP |
be403e3d | 36 | .BR ffs (): |
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37 | .nf |
38 | Since glibc 2.12: | |
39 | _XOPEN_SOURCE >= 700 | |
5c10d2c5 | 40 | || ! (_POSIX_C_SOURCE >= 200809L) |
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41 | || /* Glibc since 2.19: */ _DEFAULT_SOURCE |
42 | || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE | |
43 | Before glibc 2.12: | |
44 | none | |
45 | .fi | |
be403e3d MK |
46 | .PP |
47 | .BR ffsl (), | |
48 | .BR ffsll (): | |
9d2adbae MK |
49 | .nf |
50 | Since glibc 2.27: | |
247bbcf0 | 51 | .\" glibc commit 68fe16dd327c895c08b9ee443b234c49c13b36e9 |
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52 | _DEFAULT_SOURCE |
53 | Before glibc 2.27: | |
54 | _GNU_SOURCE | |
55 | .fi | |
fea681da | 56 | .SH DESCRIPTION |
60a90ecd MK |
57 | The |
58 | .BR ffs () | |
59 | function returns the position of the first | |
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60 | (least significant) bit set in the word \fIi\fP. |
61 | The least significant bit is position 1 and the | |
75b94dc3 | 62 | most significant position is, for example, 32 or 64. |
60a90ecd MK |
63 | The functions |
64 | .BR ffsll () | |
65 | and | |
66 | .BR ffsl () | |
67 | do the same but take | |
fea681da | 68 | arguments of possibly different size. |
47297adb | 69 | .SH RETURN VALUE |
fea681da | 70 | These functions return the position of the first bit set, |
fb84c583 MK |
71 | or 0 if no bits are set in |
72 | .IR i . | |
7eea6fc3 | 73 | .SH ATTRIBUTES |
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74 | For an explanation of the terms used in this section, see |
75 | .BR attributes (7). | |
c466875e MK |
76 | .ad l |
77 | .nh | |
067fb97f MK |
78 | .TS |
79 | allbox; | |
c466875e | 80 | lbx lb lb |
067fb97f MK |
81 | l l l. |
82 | Interface Attribute Value | |
83 | T{ | |
7eea6fc3 PH |
84 | .BR ffs (), |
85 | .BR ffsl (), | |
7eea6fc3 | 86 | .BR ffsll () |
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87 | T} Thread safety MT-Safe |
88 | .TE | |
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89 | .hy |
90 | .ad | |
91 | .sp 1 | |
3113c7f3 | 92 | .SH STANDARDS |
a9c6f658 | 93 | .BR ffs (): |
6d3452a4 | 94 | POSIX.1-2001, POSIX.1-2008, 4.3BSD. |
847e0d88 | 95 | .PP |
a385e7d7 MK |
96 | The |
97 | .BR ffsl () | |
98 | and | |
99 | .BR ffsll () | |
36f9a7fe | 100 | functions are glibc extensions. |
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101 | .SH NOTES |
102 | BSD systems have a prototype in | |
103 | .IR <string.h> . | |
47297adb | 104 | .SH SEE ALSO |
0a4f8b7b | 105 | .BR memchr (3) |