ffsl (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:

_XOPEN_SOURCE >= 700
|| ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 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).
Interface Attribute Value
ffs (), ffsl (), ffsll () Thread safety MT-Safe

CONFORMING TO

ffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.
The ffsl() and ffsll() functions are glibc extensions.

NOTES

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

SEE ALSO

memchr(3)

Information

Source
Linux kernel
OS/version
GNU
Source updated
September 15, 2017
Page created
February 9, 2018
Page generated
December 2, 2018