`bit::vector` — Special Unit Bit-Vectors

Instance methods that return some special unit bit-vectors:

1constexpr bit::vector unit_floor(bool trimmed = true) const;
2constexpr bit::vector unit_ceil(bool trimmed = true) const;

1: Return a unit bit-vector with a single 1 at the location of our final set bit.
2: Return a unit bit-vector with a single 1 at one slot past the location of our final set bit.

If the trimmed argument is true, the returned bit-vector will be as small as possible. Otherwise, in the first method, the returned bit-vector will be identical to our size; in the second method, it will be one larger than that.

In the first method, we will return an empty vector if there are no set bits.

These methods are analogous to the standard library functions std::bit_ceil and std::bit_floor that work on unsigned integers.

Example

#include <bit/bit.h>
int main()
{
    std::size_t   n = 4;
    bit::vector<> v(n);

    std::cout << "Smallest possible unit floor bit-vectors:\n";
    v.reset();
    for (std::size_t i = 0; i < n+1; v.set(i), ++i)
        std::cout << v << ".unit_floor():      " << v.unit_floor() << "\n";
    std::cout << "\n";

    std::cout << "Fixed size unit floor bit-vectors:\n";
    v.reset();
    for (std::size_t i = 0; i < n+1; v.set(i), ++i)
        std::cout << v << ".unit_floor(false): " << v.unit_floor(false) << "\n";
    std::cout << "\n";

    std::cout << "Smallest possible unit ceiling bit-vectors:\n";
    v.reset();
    for (std::size_t i = 0; i < n+1; v.set(i), ++i)
        std::cout << v << ".unit_ceil():       " << v.unit_ceil() << "\n";
    std::cout << "\n";

    std::cout << "Fixed size unit ceiling bit-vectors:\n";
    v.reset();
    for (std::size_t i = 0; i < n+1; v.set(i), ++i)
        std::cout << v << ".unit_ceil(false):  " << v.unit_ceil(false) << "\n";
}

Output

Smallest possible unit floor bit-vectors:
[0 0 0 0].unit_floor():      []
[1 0 0 0].unit_floor():      [1]
[1 1 0 0].unit_floor():      [0 1]
[1 1 1 0].unit_floor():      [0 0 1]
[1 1 1 1].unit_floor():      [0 0 0 1]

Fixed size unit floor bit-vectors:
[0 0 0 0].unit_floor(false): []
[1 0 0 0].unit_floor(false): [1 0 0 0]
[1 1 0 0].unit_floor(false): [0 1 0 0]
[1 1 1 0].unit_floor(false): [0 0 1 0]
[1 1 1 1].unit_floor(false): [0 0 0 1]

Smallest possible unit ceiling bit-vectors:
[0 0 0 0].unit_ceil():       [1]
[1 0 0 0].unit_ceil():       [0 1]
[1 1 0 0].unit_ceil():       [0 0 1]
[1 1 1 0].unit_ceil():       [0 0 0 1]
[1 1 1 1].unit_ceil():       [0 0 0 0 1]

Fixed size unit ceiling bit-vectors:
[0 0 0 0].unit_ceil(false):  [1 0 0 0 0]
[1 0 0 0].unit_ceil(false):  [0 1 0 0 0]
[1 1 0 0].unit_ceil(false):  [0 0 1 0 0]
[1 1 1 0].unit_ceil(false):  [0 0 0 1 0]
[1 1 1 1].unit_ceil(false):  [0 0 0 0 1]

See Also