FFS(3) Linux Programmer's Manual FFS(3)NAME
ffs, ffsl, ffsll - find first bit set in a word
SYNOPSIS
#include <strings.h>
int ffs(int i);
#include <string.h>
int ffsl(long int i);
int ffsll(long long int i);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
ffs():
Since glibc 2.12:
_XOPEN_SOURCE >= 700
|| ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE ||
_SVID_SOURCE
Before glibc 2.12:
none
ffsl(), ffsll():
Since glibc 2.27:
_DEFAULT_SOURCE
Before glibc 2.27:
_GNU_SOURCE
DESCRIPTION
The ffs() function returns the position of the first (least signifi‐
cant) bit set in the word i. The least significant bit is position 1
and the most significant position is, for example, 32 or 64. The func‐
tions ffsll() and ffsl() do the same but take arguments of possibly
different size.
RETURN VALUE
These functions return the position of the first bit set, or 0 if no
bits are set in i.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├───────────────────────┼───────────────┼─────────┤
│ffs(), ffsl(), ffsll() │ Thread safety │ MT-Safe │
└───────────────────────┴───────────────┴─────────┘
CONFORMING TOffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.
The ffsl() and ffsll() functions are glibc extensions.
NOTES
BSD systems have a prototype in <string.h>.
SEE ALSOmemchr(3)COLOPHON
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latest version of this page, can be found at
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GNU 2017-09-15 FFS(3)
