Add extended waveshaper primitives for fuzz and tube effects

waveshaper.h

@@ -0,0 +1,64 @@
+//
+// Extended waveshaper primitives for guitar effects
+//
+// These complement distortion.h (soft_clip, hard_clip, asymmetric_clip)
+// with additional clipping styles for fuzz, synth, and tube tones.
+//
+
+//
+// Internal soft clip helper for diode_clip below
+// Same algorithm as distortion.h's soft_clip: x / (1 + |x|)
+//
+static inline float _ws_soft_clip(float x)
+{
+	float ax = x >= 0 ? x : -x;
+	return x / (1 + ax);
+}
+
+//
+// Foldback distortion - signal folds back when exceeding threshold
+// Creates complex harmonics, useful for synth-style fuzz
+//
+static inline float fold_back(float x, float threshold)
+{
+	int iterations = 0;
+
+	if (threshold <= 0)
+		return 0;
+
+	// Limit iterations to prevent infinite loop on extreme input
+	while ((x > threshold || x < -threshold) && iterations++ < 16) {
+		if (x > threshold)
+			x = 2 * threshold - x;
+		else
+			x = -2 * threshold - x;
+	}
+	return x;
+}
+
+//
+// Tube-style waveshaper using polynomial approximation
+// Based on: y = (3x - x³) / 2, normalized for |x| <= 1
+// Provides gentle compression with soft knee
+//
+static inline float tube_clip(float x)
+{
+	// Pre-limit to avoid polynomial blowup
+	if (x > 1.5f) x = 1.5f;
+	if (x < -1.5f) x = -1.5f;
+
+	float x2 = x * x;
+	return x * (1.5f - 0.5f * x2);
+}
+
+//
+// Diode clipper emulation - asymmetric soft clip
+// Approximates silicon diode clipping (forward voltage ~0.6V)
+// ratio controls asymmetry (1.0 = symmetric, 0.5 = half negative clip)
+//
+static inline float diode_clip(float x, float ratio)
+{
+	float pos = _ws_soft_clip(x);
+	float neg = _ws_soft_clip(x * ratio) / ratio;
+	return x >= 0 ? pos : neg;
+}