Merge pull request #377 from orottier/feature/no-denormals

Flush denormal float values in audio graph processing

Author: orottier

Cargo.toml

@@ -25,6 +25,7 @@ hound = "3.5"
 hrtf = "0.8.1"
 llq = "0.1.1"
 log = "0.4"
+no_denormals = "0.1.2"
 num-complex = "0.4"
 realfft = "3.3"
 rubato = "0.14"

src/render/graph.rs

@@ -403,6 +403,7 @@ impl Graph {
                 // This may lead to logic bugs later on, but it is the best that we can do.
                 // The alternative is to crash and reboot the render thread.
                 let catch_me = AssertUnwindSafe(|| node.process(params, scope));
+
                 match panic::catch_unwind(catch_me) {
                     Ok(tail_time) => (true, tail_time),
                     Err(e) => {

src/render/thread.rs

@@ -151,10 +151,10 @@ impl RenderThread {
         let num_frames = (length + RENDER_QUANTUM_SIZE - 1) / RENDER_QUANTUM_SIZE;
 
         for _ in 0..num_frames {
-            // handle addition/removal of nodes/edges
+            // Handle addition/removal of nodes/edges
             self.handle_control_messages();
 
-            // update time
+            // Update time
             let current_frame = self
                 .frames_played
                 .fetch_add(RENDER_QUANTUM_SIZE as u64, Ordering::SeqCst);
@@ -168,8 +168,14 @@ impl RenderThread {
                 node_id: Cell::new(AudioNodeId(0)), // placeholder value
             };
 
-            // render audio graph
-            let rendered = self.graph.as_mut().unwrap().render(&scope);
+            // Render audio graph
+            let graph = self.graph.as_mut().unwrap();
+
+            // For x64 and aarch, process with denormal floats disabled (for performance, #194)
+            #[cfg(any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64"))]
+            let rendered = no_denormals::no_denormals(|| graph.render(&scope));
+            #[cfg(not(any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64")))]
+            let rendered = graph.render(&scope);
 
             rendered.channels().iter().enumerate().for_each(
                 |(channel_number, rendered_channel)| {
@@ -186,10 +192,15 @@ impl RenderThread {
     }
 
     pub fn render<S: FromSample<f32> + Clone>(&mut self, output_buffer: &mut [S]) {
-        // collect timing information
+        // Collect timing information
         let render_start = Instant::now();
 
-        // perform actual rendering
+        // Perform actual rendering
+
+        // For x64 and aarch, process with denormal floats disabled (for performance, #194)
+        #[cfg(any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64"))]
+        no_denormals::no_denormals(|| self.render_inner(output_buffer));
+        #[cfg(not(any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64")))]
         self.render_inner(output_buffer);
 
         // calculate load value and ship to control thread

tests/denormals.rs

@@ -0,0 +1,30 @@
+use web_audio_api::context::{BaseAudioContext, OfflineAudioContext};
+use web_audio_api::node::{AudioNode, AudioScheduledSourceNode};
+
+#[test]
+fn test_flush_denormals() {
+    let context = OfflineAudioContext::new(1, 128, 48000.);
+
+    let mut signal = context.create_constant_source();
+    signal.start();
+
+    let gain1 = context.create_gain();
+    gain1.gain().set_value(0.001);
+    signal.connect(&gain1);
+
+    let gain2 = context.create_gain();
+    gain2.gain().set_value(f32::MIN_POSITIVE);
+    gain1.connect(&gain2);
+
+    let gain3 = context.create_gain();
+    gain3.gain().set_value(f32::MAX);
+    gain2.connect(&gain3);
+
+    gain3.connect(&context.destination());
+
+    let output = context.start_rendering_sync();
+
+    // When denormals are flushed, we expect the output to be exactly 0.0
+    // If not, the output will be ~0.004
+    assert_eq!(output.get_channel_data(0), &[0.; 128][..]);
+}