next_bit

NAME

next_bit() - find the next set bit in a bit string

SYNOPSIS

int next_bit(string bitstring, int start);

DESCRIPTION

Returns the position of the next set (1) bit in `bitstring` that lies
strictly after position `start`, or -1 if there is no set bit past
`start`.

`bitstring` is a bit string in the compact format produced and consumed
by set_bit(), test_bit(), clear_bit() and clear_bits(): each character
stores six bits, encoded as the character value minus ' ' (0x20), so bit
N lives in character N / 6.

Because the search is exclusive of `start`, passing -1 begins the walk
before bit 0 and so finds the first set bit; feeding each result back in
as the new `start` visits every set bit in ascending order. This makes
next_bit() the idiomatic way to iterate the set bits of a bit string
without scanning every bit position by hand.

EXAMPLE

// Walk every set bit in `bits`.
for (int b = next_bit(bits, -1); b != -1; b = next_bit(bits, b)) {
    printf("bit %d is set\n", b);
}

SEE ALSO

set_bit(3), test_bit(3), clear_bit(3), clear_bits(3)