ffs(3) - Linux manual page (original) (raw)

ffs(3) Library Functions Manual ffs(3)

NAME top

   ffs, ffsl, ffsll - find first bit set in a word

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#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 top

   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 top

   These functions return the position of the first bit set, or 0 if
   no bits are set in _i_.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **ffs**(), **ffsl**(), **ffsll**()               │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   **ffs**()  POSIX.1-2001, POSIX.1-2008, 4.3BSD.

   **ffsl**()
   **ffsll**()
          GNU.

SEE ALSO top

   [memchr(3)](../man3/memchr.3.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 ffs(3)

Pages that refer to this page:memchr(3), signal-safety(7)