ffs(3)

NAME#

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

LIBRARY#

Standard C library (libc, -lc)

SYNOPSIS#

#include <strings.h>

int ffs(int \ni\n);\n
\nint ffsl(long \ni\n);\n
\nint ffsll(long long \ni\n);

ffs():

\n
    Since glibc 2.12:
\n
        _XOPEN_SOURCE >= 700
\n
            || ! (_POSIX_C_SOURCE >= 200809L)
\n
            || /* glibc >= 2.19: */ _DEFAULT_SOURCE
\n
            || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
\n
    Before glibc 2.12:
\n
        none

ffsl(), ffsll():

\n
    Since glibc 2.27:
\n
        _DEFAULT_SOURCE
\n
    Before glibc 2.27:
\n
        _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.

ATTRIBUTES#

For an explanation of the terms used in this section, see attributes(7).

STANDARDS#

ffs()

POSIX.1-2001, POSIX.1-2008, 4.3BSD.

ffsl()

ffsll()

GNU.

SEE ALSO#

memchr(3)