Reland: SIMD the main loop for k-rate Oscillator

The main processing loop for the k-rate Oscillator is updated to use
SSE2 instructions to speed up processing.

Four tests fail because we have slightly reduced accuracy.  Testing
shows that the loss of accuracy is due to using a float for
virtual_read_index in the loop instead of a double as previously.  A
implementation using a double passes all the original tests but does
show that it does lose performance.  I think the change in accuracy is
acceptable.

WebAudio Bench results from a linux machine.  In summary, the SIMD
version is about 60% as much time (about 1.75 times faster).

Without CL:
TEST	μs	MIN	Q1	MEDIAN	Q3	MAX	MEAN	STDDEV
Baseline	713	713	748	757	766	877	760.25	18.35
Oscillator	949	949	972	990	1005	1132	990.78	24.35

With CL:
TEST	μs	MIN	Q1	MEDIAN	Q3	MAX	MEAN	STDDEV
Baseline	728	728	747	756	763	908	757.46	16.81
Oscillator	521	521	549	564	581	874	566.87	27.77

Bug: 1013118
Change-Id: Ic5445cc152e960b41817f245ac306691f7c57f90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2246831Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#778579}

third_party/blink/renderer/modules/webaudio/oscillator_node.h

@@ -89,6 +89,24 @@ class OscillatorHandler final : public AudioScheduledSourceHandler {
   // Compute the output for k-rate AudioParams
   double ProcessKRate(int n, float* dest_p, double virtual_read_index) const;
 
+  // Scalar version for the main loop in ProcessKRate().  Returns the updated
+  // virtual_read_index.
+  double ProcessKRateScalar(int start_index,
+                            int n,
+                            float* dest_p,
+                            double virtual_read_index,
+                            float frequency,
+                            float rate_scale) const;
+
+  // Vectorized version (if available) for the main loop in ProcessKRate().
+  // Returns the number of elements processed and the updated
+  // virtual_read_index.
+  std::tuple<int, double> ProcessKRateVector(int n,
+                                             float* dest_p,
+                                             double virtual_read_index,
+                                             float frequency,
+                                             float rate_scale) const;
+
   // Compute the output for a-rate AudioParams
   double ProcessARate(int n,
                       float* dest_p,

third_party/blink/web_tests/webaudio/Analyser/realtimeanalyser-fftsize-reset.html

@@ -23,7 +23,7 @@
         testFFTSize(should, {
           initialFFTSize: 128,
           finalFFTSize: 1024,
-          errorThreshold: {relativeThreshold: 1.9238e-6}
+          errorThreshold: {relativeThreshold: 1.9455e-6}
         }).then(() => task.done());
       });
 
@@ -31,7 +31,7 @@
         testFFTSize(should, {
           initialFFTSize: 512,
           finalFFTSize: 256,
-          errorThreshold: {relativeThreshold: 1.8166e-6}
+          errorThreshold: {relativeThreshold: 1.8592e-6}
         }).then(() => task.done());
       });
 

third_party/blink/web_tests/webaudio/Oscillator/no-dezippering.html

@@ -57,7 +57,7 @@
               frequency1: frequency1,
               paramName: 'detune',
               newValue: detune,
-              thresholds: [1.1921e-7, 1.3114e-6],
+              thresholds: [1.1921e-7, 3.6657e-6],
             }).then(() => task.done());
           });
 

third_party/blink/web_tests/webaudio/Oscillator/osc-440hz.html

@@ -14,10 +14,10 @@
 
       // Minimum allowed SNR between the actual oscillator and the expected
       // result.  Experimentally determined.
-      let snrThreshold = 59.287;
+      let snrThreshold = 59.280;
       // Max absolute difference between actual and expected oscillator
       // outputs.  Experimentally determined.
-      let maxDiffThreshold = 1.5632e-3;
+      let maxDiffThreshold = 1.5640e-3;
 
       let audit = Audit.createTaskRunner();
 

third_party/blink/web_tests/webaudio/Oscillator/osc-negative-freq.html

@@ -27,7 +27,7 @@
         runTest(should, {
           message: 'Sum of positive and negative frequency sine oscillators',
           type: 'sine',
-          threshold: 4.1724e-7
+          threshold: 1.5349e-6
         }).then(() => task.done());
       });
 
@@ -35,7 +35,7 @@
         runTest(should, {
           message: 'Sum of positive and negative frequency square oscillators',
           type: 'square',
-          threshold: 1.4753e-6
+          threshold: 1.1496e-5
         }).then(() => task.done());
       });
 
@@ -44,7 +44,7 @@
           message:
               'Sum of positive and negative frequency sawtooth oscillators',
           type: 'sawtooth',
-          threshold: 1.4753e-6
+          threshold: 1.1506e-5
         }).then(() => task.done());
       });
 
@@ -53,7 +53,7 @@
           message:
               'Sum of positive and negative frequency triangle oscillators',
           type: 'triangle',
-          threshold: 2.9803e-7
+          threshold: 1.0133e-5
         }).then(() => task.done());
       });
 
@@ -145,7 +145,7 @@
               should(
                   actual,
                   'Sum of positive and negative frequency custom oscillators')
-                  .beCloseToArray(expected, {absoluteThreshold: 4.1724e-7});
+                  .beCloseToArray(expected, {absoluteThreshold: 2.2352e-6});
             })
             .then(() => task.done());
       });

third_party/blink/web_tests/webaudio/Oscillator/start-sampling.html

@@ -27,7 +27,7 @@
           },
           function(task, should) {
             testStartSampling(should, 1.25, {
-              error: 1.0843e-4,
+              error: 1.0880e-4,
               snrThreshold: 84.054
             }).then(task.done.bind(task));
           });
@@ -39,7 +39,7 @@
           },
           function(task, should) {
             testStartSampling(should, 1.75, {
-              error: 1.0839e-4,
+              error: 1.0844e-4,
               snrThreshold: 84.056
             }).then(task.done.bind(task));
           });
@@ -57,8 +57,8 @@
             // 1/2 frame from the preceding sampling frame.  This tests one path
             // of the internal implementation.
             testStartWithGain(should, defaultSampleRate, {
-              error: 4.1724e-7,
-              snrThreshold: 137.536
+              error: 1.9521e-6,
+              snrThreshold: 128.12
             }).then(task.done.bind(task));
           });
 
@@ -75,8 +75,8 @@
             // frame from the preceding sampling frame.  This tests one path of
             // the internal implementation.
             testStartWithGain(should, 48000, {
-              error: 4.1724e-7,
-              snrThreshold: 137.536
+              error: 1.9521e-6,
+              snrThreshold: 122.92
             }).then(task.done.bind(task));
           });
 

third_party/blink/web_tests/webaudio/PeriodicWave/ctor-periodicwave.html

@@ -134,14 +134,14 @@
         verifyPeriodicWaveOutput(
             should, {real: [0, 1], imag: [0, 1], disableNormalization: false},
             generateReference(x => Math.SQRT1_2 * (Math.sin(x) + Math.cos(x))),
-            2.7165e-5)
+            2.7225e-5)
             .then(() => task.done());
       });
 
       audit.define('3: real/imag periodicwave test', (task, should) => {
         verifyPeriodicWaveOutput(
             should, {real: [0, 1], imag: [0, 1], disableNormalization: true},
-            generateReference(x => Math.sin(x) + Math.cos(x)), 3.8416e-5)
+            generateReference(x => Math.sin(x) + Math.cos(x)), 3.8501e-5)
             .then(() => task.done());
       });