FFS(3) BSD Library Functions Manual FFS(3)NAME
ffs, ffsl, ffsll, fls, flsl, flsll -- find first or last bit set in a bit string
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <strings.h>
int
ffs(int value);
int
ffsl(long value);
int
ffsll(long long value);
int
fls(int value);
int
flsl(long value);
int
flsll(long long value);
DESCRIPTION
The ffs(), ffsl() and ffsll() functions find the first (least significant) bit set in value and return the index of that bit.
The fls(), flsl() and flsll() functions find the last (most significant) bit set in value and return the index of that bit.
Bits are numbered starting at 1, the least significant bit. A return value of zero from any of these functions means that the argument was
zero.
SEE ALSO bitstring(3)HISTORY
The ffs() function appeared in 4.3BSD. Its prototype existed previously in <string.h> before it was moved to <strings.h> for IEEE Std
1003.1-2001 (``POSIX.1'') compliance.
The ffsl(), fls() and flsl() functions appeared in FreeBSD 5.3. The ffsll() and flsll() functions appeared in FreeBSD 7.1.
BSD September 29, 2012 BSD
Check Out this Related Man Page
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:
_SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700 ||
Before glibc 2.12:
none
ffsl(), ffsll():
_GNU_SOURCE
DESCRIPTION
The ffs() function returns the position of the first (least significant) 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 functions 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.
CONFORMING TO
ffs(): 4.3BSD, POSIX.1-2001.
The ffsl() and ffsll() functions are glibc extensions.
NOTES
BSD systems have a prototype in <string.h>.
SEE ALSO memchr(3)COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2010-09-20 FFS(3)
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