Flush denormal float values in audio graph processing

Fixes #194

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

@@ -399,10 +399,21 @@ impl Graph {
             let params = AudioParamValues::from(&*nodes);
             scope.node_id.set(*index);
             let (success, tail_time) = {
+                // 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 process_fn = || no_denormals::no_denormals(|| node.process(params, scope));
+                #[cfg(not(any(
+                    target_arch = "x86",
+                    target_arch = "x86_64",
+                    target_arch = "aarch64"
+                )))]
+                let process_fn = node.process(params, scope);
+
                 // We are abusing AssertUnwindSafe here, we cannot guarantee it upholds.
                 // 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));
+                let catch_me = AssertUnwindSafe(process_fn);
+
                 match panic::catch_unwind(catch_me) {
                     Ok(tail_time) => (true, tail_time),
                     Err(e) => {

tests/denormals.rs

@@ -0,0 +1,34 @@
+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 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][..]);
+}