Add a reference follower to the benchmark

benchmarks/BM_powerFollower.cpp

@@ -33,6 +33,10 @@ public:
         follower_.setSampleRate(sfz::config::defaultSampleRate);
         follower_.setSamplesPerBlock(blockSize);
         follower_.clear();
+
+        //
+        refFollower_.init(sfz::config::defaultSampleRate);
+        refFollower_.clear();
     }
 
     void TearDown(const ::benchmark::State& /* state */)
@@ -42,10 +46,70 @@ public:
     static constexpr size_t numFrames = 65536;
     sfz::PowerFollower follower_;
     sfz::AudioBuffer<float> inputSignal_;
+
+    //
+    struct ReferenceFollower {
+        /*
+          import("stdfaust.lib");
+          process = (_, _) : + : an.amp_follower_ud(att, rel) with { att = 5e-3; rel = 200e-3; };
+        */
+
+        void init(float sampleRate)
+        {
+            fConst0 = std::min<float>(192000.0f, std::max<float>(1.0f, float(sampleRate)));
+            fConst1 = std::exp((0.0f - (200.0f / fConst0)));
+            fConst2 = (1.0f - fConst1);
+            fConst3 = std::exp((0.0f - (5.0f / fConst0)));
+            fConst4 = (1.0f - fConst3);
+        }
+        void clear()
+        {
+            for (int l0 = 0; (l0 < 2); l0 = (l0 + 1)) {
+                fRec1[l0] = 0.0f;
+            }
+            for (int l1 = 0; (l1 < 2); l1 = (l1 + 1)) {
+                fRec0[l1] = 0.0f;
+            }
+        }
+        float process(float input0, float input1)
+        {
+            float fTemp0 = std::fabs((float(input0) + float(input1)));
+            fRec1[0] = std::max<float>(fTemp0, ((fConst3 * fRec1[1]) + (fConst4 * fTemp0)));
+            fRec0[0] = ((fConst1 * fRec0[1]) + (fConst2 * fRec1[0]));
+            float output = fRec0[0];
+            fRec1[1] = fRec1[0];
+            fRec0[1] = fRec0[0];
+            return output;
+        }
+
+        float fConst0;
+        float fConst1;
+        float fConst2;
+        float fConst3;
+        float fConst4;
+        float fRec1[2];
+        float fRec0[2];
+    };
+    ReferenceFollower refFollower_;
 };
 
 constexpr size_t PowerFollowerFixture::numFrames;
 
+BENCHMARK_DEFINE_F(PowerFollowerFixture, ReferenceFollower) (benchmark::State& state)
+{
+    sfz::AudioSpan<float> inputSignal(inputSignal_);
+    auto input0 = inputSignal.getConstSpan(0);
+    auto input1 = inputSignal.getConstSpan(1);
+
+    for (auto _ : state) {
+        auto& follower = refFollower_;
+        float output = 0;
+        for (size_t i = 0, n = inputSignal.getNumFrames(); i < n; ++i)
+            output = follower.process(input0[i], input1[i]);
+        benchmark::DoNotOptimize(output);
+    }
+}
+
 BENCHMARK_DEFINE_F(PowerFollowerFixture, Follower) (benchmark::State& state)
 {
     sfz::AudioSpan<float> inputSignal(inputSignal_);
@@ -57,4 +121,5 @@ BENCHMARK_DEFINE_F(PowerFollowerFixture, Follower) (benchmark::State& state)
     }
 }
 
+BENCHMARK_REGISTER_F(PowerFollowerFixture, ReferenceFollower)->Range(1, 1);
 BENCHMARK_REGISTER_F(PowerFollowerFixture, Follower)->RangeMultiplier(2)->Range(1 << 5, 1 << 12);