ffs(3)                     Library Functions Manual                     ffs(3)

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);

   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).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |ffs (), ffsl (), ffsll ()                   | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       ffs()  POSIX.1-2001, POSIX.1-2008, 4.3BSD.

       ffsl()
       ffsll()
              GNU.

SEE ALSO
       memchr(3)

Linux man-pages 6.7               2023-11-19                            ffs(3)