add initial step sequencer implementation

sequencer/simple_seq.h

@@ -0,0 +1,66 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdlib>
+#include <vector>
+
+using namespace std;
+
+namespace trnr {
+
+enum playback_dir {
+	PB_FORWARD,
+	PB_BACKWARD,
+	PB_PENDULUM,
+	PB_RANDOM
+};
+
+struct simple_seq {
+	size_t current_pos;
+	size_t length;
+	playback_dir playback_dir;
+	vector<int> data;
+	bool pendulum_forward;
+};
+
+inline void simple_seq_init(simple_seq& s, size_t length)
+{
+	s.current_pos = 0;
+	s.length = length;
+	s.playback_dir = PB_FORWARD;
+	s.data.resize(s.length);
+	s.data.assign(s.length, 0);
+	s.pendulum_forward = true;
+}
+
+inline int simple_seq_process_step(simple_seq& s)
+{
+	// play head advancement
+	if (s.playback_dir == PB_FORWARD ||
+		s.playback_dir == PB_PENDULUM && s.pendulum_forward)
+		s.current_pos++;
+	else if (s.playback_dir == PB_BACKWARD ||
+			 s.playback_dir == PB_PENDULUM && !s.pendulum_forward)
+		s.current_pos--;
+	else if (s.playback_dir == PB_RANDOM) s.current_pos = rand() % s.length;
+
+	// play head reset
+	switch (s.playback_dir) {
+	case PB_FORWARD:
+		if (s.current_pos > s.length - 1) s.current_pos = 0;
+		break;
+	case PB_BACKWARD:
+		if (s.current_pos < 0) s.current_pos = s.length - 1;
+		break;
+	case PB_PENDULUM:
+		if (s.pendulum_forward && s.current_pos >= s.length - 1)
+			s.pendulum_forward = false;
+		else if (!s.pendulum_forward && s.current_pos <= 0) s.pendulum_forward = true;
+		break;
+	case PB_RANDOM:
+		break;
+	}
+
+	return s.data[s.current_pos];
+}
+} // namespace trnr