FFSSection: Linux Programmer's Manual (3)
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NAMEffs, ffsl, ffsll - find first bit set in a word
#include <strings.h> int ffs(int i); #define _GNU_SOURCE
#include <string.h> int ffsl(long int i); int ffsll(long long int i);
DESCRIPTIONThe 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 VALUEThese functions return the position of the first bit set, or 0 if no bits are set in i.
CONFORMING TO4.3BSD, POSIX.1-2001.
NOTESBSD systems have a prototype in <string.h>.
COLOPHONThis page is part of release 3.21 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/.