P2: level-tracker UPDATE-loop located (inline bidirectional IIR in FUN_180529fe0), structural module leveltrack (iir_first_order/bidirectional/unrolled4); scalar==unrolled verified; remaining = live A[] coeffs

dsp/leveltrack.cpp

@@ -0,0 +1,42 @@
+#include "leveltrack.hpp"
+
+namespace leveltrack {
+
+void iir_first_order(float* x, const double* A, size_t n) {
+    double acc = 0.0;
+    for (size_t i = 0; i < n; i++) {
+        double y = static_cast<double>(x[i]) * A[i] + acc;
+        acc = y;
+        x[i] = static_cast<float>(y);
+    }
+}
+
+void iir_bidirectional(float* x, const double* A, size_t n) {
+    iir_first_order(x, A, n);
+    // reverse pass over reversed indices back into x (keep array order).
+    double acc = 0.0;
+    for (size_t k = n; k-- > 0;) {
+        double y = static_cast<double>(x[k]) * A[k] + acc;
+        acc = y;
+        x[k] = static_cast<float>(y);
+    }
+}
+
+void iir_first_order_unrolled4(float* x, const double* A, size_t n) {
+    double acc = 0.0;
+    size_t i = 0;
+    for (; i + 4 <= n;) {
+        for (int u = 0; u < 4; u++, i++) {
+            double y = static_cast<double>(x[i]) * A[i] + acc;
+            acc = y;
+            x[i] = static_cast<float>(y);
+        }
+    }
+    for (; i < n; i++) {
+        double y = static_cast<double>(x[i]) * A[i] + acc;
+        acc = y;
+        x[i] = static_cast<float>(y);
+    }
+}
+
+}  // namespace leveltrack