Embedded C++: Templates and constexpr

Compile-time work, zero run-time cost.

A template builds code for many types from one definition. A fixed-size buffer class can take its length as a template parameter, so memory is sized at compile time.

constexpr lets the compiler compute values such as tables or baud-rate divisors during the build. The chip just reads the finished result.

Both features avoid dynamic memory, which is ideal for small devices.

template <typename T, unsigned N>
class Buffer {
  public:
    void put(T v) { data[idx++ % N] = v; }
  private:
    T data[N]; unsigned idx = 0;
};

constexpr unsigned divisor(unsigned clk, unsigned baud) { return clk / (16 * baud); }
Buffer<unsigned char, 32> rx;