FFS(3) | Library Functions Manual | FFS(3)

# NAME

`ffs` —
find first bit set in a bit string

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

`#include <strings.h>`

int
`ffs`(int value);

# DESCRIPTION

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.

# SEE ALSO

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

# STANDARDS

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

# HISTORY

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