ffsl(3) - f39

1ffs(3)                     Library Functions Manual                     ffs(3)
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NAME

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

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <strings.h>
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14       int ffs(int i);
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16       #include <string.h>
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18       int ffsl(long i);
19       int ffsll(long long i);
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21   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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23       ffs():
24           Since glibc 2.12:
25               _XOPEN_SOURCE >= 700
26                   || ! (_POSIX_C_SOURCE >= 200809L)
27                   || /* glibc >= 2.19: */ _DEFAULT_SOURCE
28                   || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
29           Before glibc 2.12:
30               none
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32       ffsl(), ffsll():
33           Since glibc 2.27:
34               _DEFAULT_SOURCE
35           Before glibc 2.27:
36               _GNU_SOURCE
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DESCRIPTION

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

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

50       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
51       tributes(7).
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53       ┌────────────────────────────────────────────┬───────────────┬─────────┐
54       │Interface                                   │ Attribute     │ Value   │
55       ├────────────────────────────────────────────┼───────────────┼─────────┤
56       │ffs(), ffsl(), ffsll()                      │ Thread safety │ MT-Safe │
57       └────────────────────────────────────────────┴───────────────┴─────────┘
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VERSIONS

60       BSD systems have a prototype in <string.h>.
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STANDARDS

63       ffs()  POSIX.1-2001, POSIX.1-2008, 4.3BSD.
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65       ffsl()
66       ffsll()
67              GNU.
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