1FFS(3)                     Linux Programmer's Manual                    FFS(3)
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NAME

6       ffs, ffsl, ffsll - find first bit set in a word
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SYNOPSIS

9       #include <strings.h>
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11       int ffs(int i);
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13       #include <string.h>
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15       int ffsl(long int i);
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17       int ffsll(long long int i);
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19   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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21       ffs():
22           Since glibc 2.12:
23                   _XOPEN_SOURCE >= 700
24                   || ! (_POSIX_C_SOURCE >= 200809L)
25                   || /* Glibc since 2.19: */ _DEFAULT_SOURCE
26                   || /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
27               _SVID_SOURCE
28           Before glibc 2.12:
29               none
30       ffsl(), ffsll():
31           Since glibc 2.27:
32                   _DEFAULT_SOURCE
33           Before glibc 2.27:
34                   _GNU_SOURCE
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DESCRIPTION

37       The ffs() function returns the position of the  first  (least  signifi‐
38       cant)  bit  set in the word i.  The least significant bit is position 1
39       and the most significant position is, for example, 32 or 64.  The func‐
40       tions  ffsll()  and  ffsl()  do the same but take arguments of possibly
41       different size.
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RETURN VALUE

44       These functions return the position of the first bit set, or  0  if  no
45       bits are set in i.
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ATTRIBUTES

48       For   an   explanation   of   the  terms  used  in  this  section,  see
49       attributes(7).
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51       ┌───────────────────────┬───────────────┬─────────┐
52       │Interface              │ Attribute     │ Value   │
53       ├───────────────────────┼───────────────┼─────────┤
54       │ffs(), ffsl(), ffsll() │ Thread safety │ MT-Safe │
55       └───────────────────────┴───────────────┴─────────┘

CONFORMING TO

57       ffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.
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59       The ffsl() and ffsll() functions are glibc extensions.
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NOTES

62       BSD systems have a prototype in <string.h>.
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SEE ALSO

65       memchr(3)
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COLOPHON

68       This page is part of release 4.15 of the Linux  man-pages  project.   A
69       description  of  the project, information about reporting bugs, and the
70       latest    version    of    this    page,    can     be     found     at
71       https://www.kernel.org/doc/man-pages/.
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75GNU                               2017-09-15                            FFS(3)
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