polyline: Added encode/decodeSignedIntegers() functions

src/ol/parser/polyline.js

@@ -72,6 +72,50 @@ ol.parser.polyline.decodeFlatCoordinates = function(encoded, opt_dimension) {
 };
 
 
+/**
+ * Encode a list of signed integers and return an encoded string
+ *
+ * Attention: This function will modify the passed array!
+ *
+ * @param {Array.<number>} numbers A list of signed integers.
+ * @return {string} The encoded string.
+ */
+ol.parser.polyline.encodeSignedIntegers = function(numbers) {
+  var numbersLength = numbers.length;
+  for (var i = 0; i < numbersLength; ++i) {
+    var num = numbers[i];
+
+    var signedNum = num << 1;
+    if (num < 0) {
+      signedNum = ~(signedNum);
+    }
+
+    numbers[i] = signedNum;
+  }
+
+  return ol.parser.polyline.encodeUnsignedIntegers(numbers);
+};
+
+
+/**
+ * Decode a list of signed integers from an encoded string
+ *
+ * @param {string} encoded An encoded string.
+ * @return {Array.<number>} A list of signed integers.
+ */
+ol.parser.polyline.decodeSignedIntegers = function(encoded) {
+  var numbers = ol.parser.polyline.decodeUnsignedIntegers(encoded);
+
+  var numbersLength = numbers.length;
+  for (var i = 0; i < numbersLength; ++i) {
+    var num = numbers[i];
+    numbers[i] = (num & 1) ? ~(num >> 1) : (num >> 1);
+  }
+
+  return numbers;
+};
+
+
 /**
  * Encode a list of unsigned integers and return an encoded string
  *

test/spec/ol/parser/polyline.test.js

@@ -27,6 +27,28 @@ describe('ol.parser.polyline', function() {
   });
 
 
+  var signedIntegers = [0, 15, -1, -16, 16, 1];
+  var encodedSignedIntegers = '?]@^_@A';
+
+  describe('encodeSignedIntegers', function() {
+    it('returns expected value', function() {
+      var encodeSignedIntegers = ol.parser.polyline.encodeSignedIntegers;
+
+      expect(encodeSignedIntegers(
+          signedIntegers.slice())).toEqual(encodedSignedIntegers);
+    });
+  });
+
+  describe('decodeSignedIntegers', function() {
+    it('returns expected value', function() {
+      var decodeSignedIntegers = ol.parser.polyline.decodeSignedIntegers;
+
+      expect(decodeSignedIntegers(
+          encodedSignedIntegers)).toEqual(signedIntegers);
+    });
+  });
+
+
   var unsignedIntegers = [0, 30, 1, 31, 32, 2, 174];
   var encodedUnsignedIntegers = '?]@^_@AmD';