getOrPutInternal

        fn getOrPutInternal(self: *Self, key: anytype, ctx: anytype, header: *IndexHeader, comptime I: type) GetOrPutResult {
            const slice = self.entries.slice();
            const hashes_array = if (store_hash) slice.items(.hash) else {};
            const keys_array = slice.items(.key);
            const values_array = slice.items(.value);
            const indexes = header.indexes(I);

            const h = checkedHash(ctx, key);
            const start_index = safeTruncate(usize, h);
            const end_index = start_index +% indexes.len;

            var index = start_index;
            var distance_from_start_index: I = 0;
            while (index != end_index) : ({
                index +%= 1;
                distance_from_start_index += 1;
            }) {
                var slot = header.constrainIndex(index);
                var slot_data = indexes[slot];

                // If the slot is empty, there can be no more items in this run.
                // We didn't find a matching item, so this must be new.
                // Put it in the empty slot.
                if (slot_data.isEmpty()) {
                    const new_index = self.entries.addOneAssumeCapacity();
                    indexes[slot] = .{
                        .distance_from_start_index = distance_from_start_index,
                        .entry_index = @as(I, @intCast(new_index)),
                    };

                    // update the hash if applicable
                    if (store_hash) hashes_array.ptr[new_index] = h;

                    return .{
                        .found_existing = false,
                        .key_ptr = &keys_array.ptr[new_index],
                        .value_ptr = &values_array.ptr[new_index],
                        .index = new_index,
                    };
                }

                // This pointer survives the following append because we call
                // entries.ensureTotalCapacity before getOrPutInternal.
                const i = slot_data.entry_index;
                const hash_match = if (store_hash) h == hashes_array[i] else true;
                if (hash_match and checkedEql(ctx, key, keys_array[i], i)) {
                    return .{
                        .found_existing = true,
                        .key_ptr = &keys_array[slot_data.entry_index],
                        .value_ptr = &values_array[slot_data.entry_index],
                        .index = slot_data.entry_index,
                    };
                }

                // If the entry is closer to its target than our current distance,
                // the entry we are looking for does not exist.  It would be in
                // this slot instead if it was here.  So stop looking, and switch
                // to insert mode.
                if (slot_data.distance_from_start_index < distance_from_start_index) {
                    // In this case, we did not find the item. We will put a new entry.
                    // However, we will use this index for the new entry, and move
                    // the previous index down the line, to keep the max distance_from_start_index
                    // as small as possible.
                    const new_index = self.entries.addOneAssumeCapacity();
                    if (store_hash) hashes_array.ptr[new_index] = h;
                    indexes[slot] = .{
                        .entry_index = @as(I, @intCast(new_index)),
                        .distance_from_start_index = distance_from_start_index,
                    };
                    distance_from_start_index = slot_data.distance_from_start_index;
                    var displaced_index = slot_data.entry_index;

                    // Find somewhere to put the index we replaced by shifting
                    // following indexes backwards.
                    index +%= 1;
                    distance_from_start_index += 1;
                    while (index != end_index) : ({
                        index +%= 1;
                        distance_from_start_index += 1;
                    }) {
                        slot = header.constrainIndex(index);
                        slot_data = indexes[slot];
                        if (slot_data.isEmpty()) {
                            indexes[slot] = .{
                                .entry_index = displaced_index,
                                .distance_from_start_index = distance_from_start_index,
                            };
                            return .{
                                .found_existing = false,
                                .key_ptr = &keys_array.ptr[new_index],
                                .value_ptr = &values_array.ptr[new_index],
                                .index = new_index,
                            };
                        }

                        if (slot_data.distance_from_start_index < distance_from_start_index) {
                            indexes[slot] = .{
                                .entry_index = displaced_index,
                                .distance_from_start_index = distance_from_start_index,
                            };
                            displaced_index = slot_data.entry_index;
                            distance_from_start_index = slot_data.distance_from_start_index;
                        }
                    }
                    unreachable;
                }
            }
            unreachable;
        }