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NAME

ffs, ffsl, ffsll — find first bit set in a bit string

SYNOPSIS

#include <strings.h>

int
ffs(int value);

int
ffsl(long value);

int
ffsll(long long value);

DESCRIPTION

The ffs(), ffsl() and ffsll() functions find the first bit set in value and returns the index of that bit. Bits are numbered starting from 1, starting at the rightmost bit. A return value of 0 means that the argument was zero.

SEE ALSO

bit_ffs(3)

STANDARDS

The ffs() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”). The ffsl() and ffsll() functions conform to IEEE Std 1003.1-2024 (“POSIX.1”).

HISTORY

The ffs() function first appeared in 4.2BSD. The ffsl() and ffsll() functions first appeared in OpenBSD 7.9.