ffs(3)

NAME

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

SYNOPSIS

   #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():
       _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 
   

CONFORMING TO

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

   The ffsl() and ffsll() functions are glibc extensions.

NOTES

   BSD systems have a prototype in <string.h>.

SEE ALSO

   memchr(3)

COLOPHON

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