NAME¶

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

LIBRARY¶

Standard C library (libc, -lc)

SYNOPSIS¶

#include <strings.h>

int ffs(int i);
int ffsl(long i);
int ffsll(long long i);

ffs():

    Since glibc 2.12:


        _XOPEN_SOURCE >= 700


            || ! (_POSIX_C_SOURCE >= 200809L)


            || /* glibc >= 2.19: */ _DEFAULT_SOURCE


            || /* glibc <= 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 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)