Fast path and benchmark for ConstantSourceNode

Author: orottier

benches/my_benchmark.rs

@@ -50,6 +50,17 @@ pub fn bench_audio_buffer_decode() {
     assert_eq!(buffer.length(), 101129);
 }
 
+pub fn bench_constant_source() {
+    let mut ctx = OfflineAudioContext::new(2, black_box(SAMPLES), SAMPLE_RATE);
+    let mut src = ctx.create_constant_source();
+
+    src.connect(&ctx.destination());
+    src.start_at(1.);
+    src.stop_at(9.);
+
+    assert_eq!(ctx.start_rendering_sync().length(), SAMPLES);
+}
+
 pub fn bench_sine() {
     let mut ctx = OfflineAudioContext::new(2, black_box(SAMPLES), SAMPLE_RATE);
     let mut osc = ctx.create_oscillator();
@@ -301,6 +312,7 @@ macro_rules! iai_or_criterion {
 iai_or_criterion!(
     bench_ctor,
     bench_audio_buffer_decode,
+    bench_constant_source,
     bench_sine,
     bench_sine_gain,
     bench_sine_gain_delay,

src/node/constant_source.rs

@@ -201,23 +201,33 @@ impl AudioProcessor for ConstantSourceRenderer {
 
         let offset = params.get(&self.offset);
         let output_channel = output.channel_data_mut(0);
-        let mut current_time = scope.current_time;
-
-        output_channel
-            .iter_mut()
-            .zip(offset.iter().cycle())
-            .for_each(|(o, &value)| {
-                if current_time < self.start_time || current_time >= self.stop_time {
-                    *o = 0.;
-                } else {
-                    // as we pick values directly from the offset param which is already
-                    // computed at sub-sample accuracy, we don't need to do more than
-                    // copying the values to their right place.
-                    *o = value;
-                }
-
-                current_time += dt;
-            });
+
+        // fast path
+        if offset.len() == 1
+            && self.start_time <= scope.current_time
+            && self.stop_time > next_block_time
+        {
+            output_channel.fill(offset[0]);
+        } else {
+            // sample accurate path
+            let mut current_time = scope.current_time;
+
+            output_channel
+                .iter_mut()
+                .zip(offset.iter().cycle())
+                .for_each(|(o, &value)| {
+                    if current_time < self.start_time || current_time >= self.stop_time {
+                        *o = 0.;
+                    } else {
+                        // as we pick values directly from the offset param which is already
+                        // computed at sub-sample accuracy, we don't need to do more than
+                        // copying the values to their right place.
+                        *o = value;
+                    }
+
+                    current_time += dt;
+                });
+        }
 
         // tail_time false when output has ended this quantum
         let still_running = self.stop_time >= next_block_time;