__ffs(9) centos man page | unix.com

__FFS(9)						     Basic C Library Functions							  __FFS(9)

NAME
       __ffs - find first set bit in word

SYNOPSIS
       unsigned long __ffs(unsigned long word);

ARGUMENTS
       word
	   The word to search

DESCRIPTION
       Undefined if no bit exists, so code should check against 0 first.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014								  __FFS(9)