actualChecksum

    fn actualChecksum(f: *AllocFooter, s: *SafeAllocator) u32 {
        if (f.isExtended()) {
            const len = f.extended().len;
            const addr: usize = if (s.isLarge(len, f.userAlign()))
                @intFromPtr(f.extended().container.large_entry)
            else
                @intFromPtr(f.extended().container.bucket_prev);

            const len_bytes: [@sizeOf(usize)]u8 = @bitCast(len);
            const container: [@sizeOf(usize)]u8 = @bitCast(addr);
            const regular_bytes: [2]u8 = @bitCast(f.data);
            const data_bytes = len_bytes ++ container ++ regular_bytes;

            return @truncate(std.hash.Wyhash.hash(@truncate(@intFromPtr(f)), &data_bytes));
        }
        return @truncate(std.hash.int(@as(u16, @bitCast(f.data)) ^ @intFromPtr(f)));
    }