ffs(3) Library Functions Manual ffs(3) 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); #include <string.h> 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 signifi- cant) 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 func- tions 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 at- tributes(7). ┌────────────────────────────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├────────────────────────────────────────────┼───────────────┼─────────┤ │ffs(), ffsl(), ffsll() │ Thread safety │ MT-Safe │ └────────────────────────────────────────────┴───────────────┴─────────┘ STANDARDS 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) Linux man-pages 6.03 2023-02-05 ffs(3)
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