FFS(3) manual page
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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:
- _SVID_SOURCE || _BSD_SOURCE
|| _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700 ||
- Before glibc 2.12:
none
ffsl(),
ffsll():
_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.
The ffs(), ffsl(), and ffsll() functions are thread-safe.
ffs(): 4.3BSD, POSIX.1-2001.
The ffsl() and ffsll() functions
are glibc extensions.
BSD systems have a prototype in <string.h>.
memchr(3)
This page is part of release 3.78 of the Linux man-pages project.
A description of the project, information about reporting bugs, and the
latest version of this page, can be found at http://www.kernel.org/doc/man-pages/.
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