FFS(3) BSD Programmer's Manual FFS(3)
ffs - find first bit set in a bit string
The ffs() function finds the first bit set in value and returns the index
of that bit. Bits are numbered starting from 1, starting at the right-
most bit. A return value of 0 means that the argument was zero.
The ffs() function appeared in 4.3BSD.
4.4BSD April 19, 1994 1