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 6.9.1                              2024-05-02                                             ffs(3)