fls(3) [freebsd man page]
FFS(3) BSD Library Functions Manual FFS(3) NAME
ffs, ffsl, ffsll, fls, flsl, flsll -- find first or last bit set in a bit string LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <strings.h> int ffs(int value); int ffsl(long value); int ffsll(long long value); int fls(int value); int flsl(long value); int flsll(long long value); DESCRIPTION
The ffs(), ffsl() and ffsll() functions find the first (least significant) bit set in value and return the index of that bit. The fls(), flsl() and flsll() functions find the last (most significant) bit set in value and return the index of that bit. Bits are numbered starting at 1, the least significant bit. A return value of zero from any of these functions means that the argument was zero. SEE ALSO
bitstring(3) HISTORY
The ffs() function appeared in 4.3BSD. Its prototype existed previously in <string.h> before it was moved to <strings.h> for IEEE Std 1003.1-2001 (``POSIX.1'') compliance. The ffsl(), fls() and flsl() functions appeared in FreeBSD 5.3. The ffsll() and flsll() functions appeared in FreeBSD 7.1. BSD
September 29, 2012 BSD
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FFS(3) Linux Programmer's Manual 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: _SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700 || 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. CONFORMING TO
ffs(): 4.3BSD, POSIX.1-2001. The ffsl() and ffsll() functions are glibc extensions. NOTES
BSD systems have a prototype in <string.h>. SEE ALSO
memchr(3) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2010-09-20 FFS(3)