ffs, ffsl, ffsll - find first bit set in a word
#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
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.
These functions return the position of the first bit set, or 0 if no bits are
set in
i.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| ffs (), ffsl (), ffsll () |
Thread safety |
MT-Safe |
ffs(): POSIX.1-2001, POSIX.1-2008, 4.3BSD.
The
ffsl() and
ffsll() functions are glibc extensions.
BSD systems have a prototype in
<string.h>.
memchr(3)