Maybe works?

state.h

@@ -9,22 +9,22 @@
 
 typedef struct {
 	float		clock_bpm;
-
 	float		vco_freq;
 	float		vco_volume;
 	vco_mode_t	vco_mode;
-
 	float		filter_freq;
 	float		filter_resonance;
-
 	float		env1_attack;
-	float		env1_release;
+	float		env1_decay;
 	float		env2_attack;
-	float		env2_release;
-
+	float		env2_decay;
 	float		reverb_amount;
 	bool		quant_enabled;
 	bool		amen_enabled;
+	float		beat_samples;
+	float		playback_rate;
+	float		clock_inc;
+	uint32_t	amen_inc_fp;
 } state_t;
 
 static inline float map_linear(float v, float min, float max) {
@@ -32,12 +32,17 @@ static inline float map_linear(float v, float min, float max) {
 }
 
 static inline float map_exponential(float v, float min, float max) {
-	return min + powf(max / min, v);
+	if (min == 0.0f) min = 1e-6f; 
+	return min * powf(max / min, v);
 }
 
 static inline float map_squared(float v, float min, float max) {
 	return min + (v * v) * (max - min);
 }
 
+static inline float max_constant(float _0, float val, float _1) {
+	return val;
+}
+
 void update_state(state_t* state, input_t* input);