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FFS(3) Library Functions Manual FFS(3)

ffsfind first bit set in a bit string

library “libc”

#include <strings.h>

int
ffs(int value);

The () 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.

bitstring(3), ffs32(3), popcount(3)

The ffs() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

The ffs() function appeared in 4.3BSD. The prototype for it existed previously in the <string.h> header before it was moved to <strings.h> for POSIX compliance.

April 28, 2010 NetBSD-9.2