ffsll(3) - f38

1ffs(3)                     Library Functions Manual                     ffs(3)
2
3
4

NAME

6       ffs, ffsl, ffsll - find first bit set in a word
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <strings.h>
13
14       int ffs(int i);
15
16       #include <string.h>
17
18       int ffsl(long i);
19       int ffsll(long long i);
20
21   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
22
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
31
32       ffsl(), ffsll():
33           Since glibc 2.27:
34               _DEFAULT_SOURCE
35           Before glibc 2.27:
36               _GNU_SOURCE
37

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.
44

RETURN VALUE

46       These  functions  return  the position of the first bit set, or 0 if no
47       bits are set in i.
48

ATTRIBUTES

50       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
51       tributes(7).
52
53       ┌────────────────────────────────────────────┬───────────────┬─────────┐
54       │Interface                                   │ Attribute     │ Value   │
55       ├────────────────────────────────────────────┼───────────────┼─────────┤
56       │ffs(), ffsl(), ffsll()                      │ Thread safety │ MT-Safe │
57       └────────────────────────────────────────────┴───────────────┴─────────┘
58

VERSIONS

60       BSD systems have a prototype in <string.h>.
61

STANDARDS

63       ffs()  POSIX.1-2001, POSIX.1-2008, 4.3BSD.
64
65       ffsl()
66       ffsll()
67              GNU.
68