ffs - find first bit set in a word

NAME  LIBRARY  SYNOPSIS  DESCRIPTION  RETURN VALUE  ATTRIBUTES  VERSIONS  STANDARDS  SEE ALSO 

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);

#include <string.h>

int ffsl(long i);
int ffsll(long long
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 >= 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).

VERSIONS

BSD systems have a prototype in <string.h>.

STANDARDS

ffs()

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

ffsl()

ffsll()

GNU.

SEE ALSO

memchr(3)


Updated 2024-01-29 - jenkler.se | uex.se