First pass idLib conversion from hex rays4.

source/shared/idlib/math/decay.cpp

@@ -0,0 +1,53 @@
+#include "decay.h"
+
+#include <cmath>
+
+idParametricDecay::idParametricDecay()
+    : delta(0.0f)
+    , linear(0.0f)
+    , t0(0.0f)
+    , tdelta(0.0f)
+    , lambda(0.0f) {
+}
+
+void idParametricDecay::Init(
+    const float newDelta,
+    const float newLinear,
+    const float newT0,
+    const float newTDelta,
+    const float newLambda
+) {
+    delta = newDelta;
+    linear = newLinear;
+    t0 = newT0;
+    tdelta = newTDelta;
+    lambda = newLambda;
+}
+
+void idParametricDecay::SetTZero(const float newT0) {
+    t0 = newT0;
+}
+
+void idParametricDecay::SetDelta(const float newDelta) {
+    delta = newDelta;
+}
+
+float idParametricDecay::Evaluate(const float t) const {
+    if (t < t0) {
+        return delta;
+    }
+
+    const float elapsed = t - t0;
+    if (elapsed > tdelta) {
+        return 0.0f;
+    }
+
+    const float normalizedTime = elapsed / tdelta;
+    const float exponential = std::pow(
+        0.5f,
+        elapsed / (lambda * tdelta)
+    );
+    return ((1.0f - linear) * exponential
+        + (1.0f - normalizedTime) * linear) * delta;
+}
+