From f47684add3825a7865ce9094f4e558067c80c20a Mon Sep 17 00:00:00 2001
From: Hugh Rawlinson <hughr2005@gmail.com>
Date: Mon, 13 Jan 2020 22:11:18 -0500
Subject: [PATCH] WIP

---
 src/extractors/autocorrelation.js             |  33 ++-
 test/extractors/autocorrelation.js            |  13 +
 .../autocorrelationTestData/sin128.ac.json    | 257 ++++++++++++++++++
 .../autocorrelationTestData/sin128.json       | 130 +++++++++
 4 files changed, 422 insertions(+), 11 deletions(-)
 create mode 100644 test/extractors/autocorrelationTestData/sin128.ac.json
 create mode 100644 test/extractors/autocorrelationTestData/sin128.json

diff --git a/src/extractors/autocorrelation.js b/src/extractors/autocorrelation.js
index 44438e27..14730387 100644
--- a/src/extractors/autocorrelation.js
+++ b/src/extractors/autocorrelation.js
@@ -1,3 +1,21 @@
+function zeroIfOutOfBound(i, f) {
+  if (i < 0) {
+    return 0;
+  }
+  if (i >= f.length - 1) {
+    return 0;
+  }
+  return f[i];
+}
+
+function phi(t, f) {
+  var acc = 0;
+  for (var i = 0; i < f.length; i++) {
+    acc += f[i] * zeroIfOutOfBound(i + t, f);
+  }
+  return acc;
+}
+
 export default function autocorrelation() {
   if (typeof arguments[0].signal !== 'object') {
     throw new TypeError();
@@ -5,16 +23,9 @@ export default function autocorrelation() {
 
   const arr = arguments[0].signal;
 
-  var ac = new Float32Array(arr.length);
-  for (var lag = 0; lag < arr.length; lag++) {
-    var value = 0;
-    for (var index = 0; index < arr.length - lag; index++) {
-      let a = arr[index];
-      let otherindex = index - lag;
-      let b = otherindex >= 0 ? arr[otherindex] : 0;
-      value = value + a * b;
-    }
-    ac[lag] = value;
+  var ac = new Float32Array(arr.length*2);
+  for (var lag = -1*arr.length; lag < arr.length; lag++) {
+    ac[lag + arr.length] = phi(lag, arr);
   }
   return ac;
-}
+};
diff --git a/test/extractors/autocorrelation.js b/test/extractors/autocorrelation.js
index 9bf4114c..b3a76f8c 100644
--- a/test/extractors/autocorrelation.js
+++ b/test/extractors/autocorrelation.js
@@ -4,8 +4,21 @@ var TestData = require('../TestData');
 
 // Setup
 var autocorrelation = require('../../dist/node/extractors/autocorrelation');
+var sin128 = require('./autocorrelationTestData/sin128.json');
+var sin128AC = require('./autocorrelationTestData/sin128.ac.json');
 
 describe('autocorrelation', function () {
+  it.only('should blah', function(done) {
+    // assert.deepEqual(autocorrelation({signal: sin128}), new Float32Array(sin128AC));
+    autocorrelation({signal:sin128}).forEach((element, index) => {
+      try {
+        assert.approximately(element, sin128AC[index], 5);
+      } catch (e) {
+        throw Error(`index: ${index}: ${element}, ${sin128AC[index]} \n${e.message}`);
+      }
+    });
+  });
+
   it('should return correct autocorrelation value', function (done) {
     var en = autocorrelation({
       signal:TestData.VALID_SIGNAL,
diff --git a/test/extractors/autocorrelationTestData/sin128.ac.json b/test/extractors/autocorrelationTestData/sin128.ac.json
new file mode 100644
index 00000000..f8e2ef1e
--- /dev/null
+++ b/test/extractors/autocorrelationTestData/sin128.ac.json
@@ -0,0 +1,257 @@
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diff --git a/test/extractors/autocorrelationTestData/sin128.json b/test/extractors/autocorrelationTestData/sin128.json
new file mode 100644
index 00000000..4e735f7d
--- /dev/null
+++ b/test/extractors/autocorrelationTestData/sin128.json
@@ -0,0 +1,130 @@
+[
+    0,
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\ No newline at end of file