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FFS(3) FreeBSD 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), bitset(9)
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.
FreeBSD 14.0-RELEASE-p6 October 17, 2015 FreeBSD 14.0-RELEASE-p6