<xstd/bits/bit_span/bit_subspan.hpp>

bit_subspan

template<bit_blocks Blocks, size_t Extent, size_t N>
class bit_subspan {
public:
  // as bit_span, with
  static constexpr size_t extent = Extent;

  template<class OtherBlocks, size_t OtherExtent>
      requires see below
    constexpr explicit(Extent != dynamic_extent) bit_subspan(const bit_subspan<OtherBlocks, OtherExtent, N>& other)
      noexcept;
};

A window: the part of a bit_span or of another window that first, last and subspan return. As bit_span, with:

• It stores what span stores, the start split over a pointer and a position because bits are not addressable, and the count where Extent is dynamic_extent: three words, or two at a static extent.
• It is made by first, last and subspan, which on a window return a window over the same Blocks and N. Between extents the rule is span's: a static window converts to a dynamic one implicitly, and a dynamic one to a static one explicitly. Preconditions: the sizes agree. A window of mutable bits converts to one of const bits.
• At a static extent, size, empty and max_size are constants of the type, as for basic_bit_array; at the dynamic extent they are functions, and max_size() is size().
• A write to a window masks its end blocks, so the bits around it, which share those blocks, are untouched.