FFS(3) - man page online | library functions

Find first bit set in a word.

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.
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 This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at
GNU 2015-08-08 FFS(3)
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ffs(3) referred by memchr(3)
refer to attributes(7) | feature_test_macros(7) | memchr(3)