dart: use floor and integer tests (#728)

Author: drinckes

dart/lib/src/open_location_code.dart

@@ -254,11 +254,6 @@ bool isFull(String code) {
 /// * [codeLength]: The number of significant digits in the output code, not
 /// including any separator characters.
 String encode(num latitude, num longitude, {int codeLength = pairCodeLength}) {
-  if (codeLength < minDigitCount ||
-      (codeLength < pairCodeLength && codeLength.isOdd)) {
-    throw ArgumentError('Invalid Open Location Code length: $codeLength');
-  }
-  codeLength = min(maxDigitCount, codeLength);
   var integers = locationToIntegers(latitude, longitude);
   return encodeIntegers(integers[0], integers[1], codeLength);
 }
@@ -269,7 +264,7 @@ List<int> locationToIntegers(num latitude, num longitude) {
   // Convert latitude into a positive integer clipped into the range 0-(just
   // under 180*2.5e7). Latitude 90 needs to be adjusted to be just less, so the
   // returned code can also be decoded.
-  var latVal = (latitude * finalLatPrecision).round().toInt();
+  var latVal = (latitude * finalLatPrecision).floor().toInt();
   latVal += latitudeMax * finalLatPrecision;
   if (latVal < 0) {
     latVal = 0;
@@ -278,7 +273,7 @@ List<int> locationToIntegers(num latitude, num longitude) {
   }
   // Convert longitude into a positive integer and normalise it into the range
   // 0-360*8.192e6.
-  var lngVal = (longitude * finalLngPrecision).round().toInt();
+  var lngVal = (longitude * finalLngPrecision).floor().toInt();
   lngVal += longitudeMax * finalLngPrecision;
   if (lngVal < 0) {
     // Dart's % operator differs from other languages in that it returns the
@@ -293,6 +288,11 @@ List<int> locationToIntegers(num latitude, num longitude) {
 
 /// Encode a location into an Open Location Code.
 String encodeIntegers(int latVal, int lngVal, int codeLength) {
+  if (codeLength < minDigitCount ||
+      (codeLength < pairCodeLength && codeLength.isOdd)) {
+    throw ArgumentError('Invalid Open Location Code length: $codeLength');
+  }
+  codeLength = min(maxDigitCount, codeLength);
   List<String> code = List<String>.filled(maxDigitCount + 1, '');
   code[separatorPosition] = separator;
 

dart/test/encode_test.dart

@@ -19,19 +19,71 @@ import 'package:test/test.dart';
 import 'utils.dart';
 
 // code,lat,lng,latLo,lngLo,latHi,lngHi
-void checkEncodeDecode(String csvLine) {
+void checkEncodeDegrees(String csvLine) {
   var elements = csvLine.split(',');
   num lat = double.parse(elements[0]);
   num lng = double.parse(elements[1]);
-  int len = int.parse(elements[2]);
-  var want = elements[3];
+  int len = int.parse(elements[4]);
+  var want = elements[5];
   var got = olc.encode(lat, lng, codeLength: len);
   expect(got, equals(want));
 }
 
+void checkEncodeIntegers(String csvLine) {
+  var elements = csvLine.split(',');
+  int lat = int.parse(elements[2]);
+  int lng = int.parse(elements[3]);
+  int len = int.parse(elements[4]);
+  var want = elements[5];
+  var got = olc.encodeIntegers(lat, lng, len);
+  expect(got, equals(want));
+}
+
+void checkLocationToIntegers(String csvLine) {
+  var elements = csvLine.split(',');
+  num latDegrees = double.parse(elements[0]);
+  num lngDegrees = double.parse(elements[1]);
+  int latInteger = int.parse(elements[2]);
+  int lngInteger = int.parse(elements[3]);
+  var got = olc.locationToIntegers(latDegrees, lngDegrees);
+  // Due to floating point precision limitations, we may get values 1 less than expected.
+  expect(got[0], lessThanOrEqualTo(latInteger));
+  expect(got[0] + 1, greaterThanOrEqualTo(latInteger));
+  expect(got[1], lessThanOrEqualTo(lngInteger));
+  expect(got[1] + 1, greaterThanOrEqualTo(lngInteger));
+}
+
 void main() {
-  test('Check encode decode', () {
-    csvLinesFromFile('encoding.csv').forEach(checkEncodeDecode);
+  // Encoding from degrees permits a small percentage of errors.
+  // This is due to floating point precision limitations.
+  test('Check encode from degrees', () {
+    // The proportion of tests that we will accept generating a different code.
+    // This should not be significantly different from any other implementation.
+    num allowedErrRate = 0.05;
+    int errors = 0;
+    int tests = 0;
+    csvLinesFromFile('encoding.csv').forEach((csvLine) {
+      tests++;
+      var elements = csvLine.split(',');
+      num lat = double.parse(elements[0]);
+      num lng = double.parse(elements[1]);
+      int len = int.parse(elements[4]);
+      var want = elements[5];
+      var got = olc.encode(lat, lng, codeLength: len);
+      if (got != want) {
+        print("ENCODING DIFFERENCE: Got '$got', expected '$want'");
+        errors++;
+      }
+    });
+    expect(errors / tests, lessThanOrEqualTo(allowedErrRate));
+  });
+
+  test('Check encode from integers', () {
+    csvLinesFromFile('encoding.csv').forEach(checkEncodeIntegers);
+  });
+
+  test('Check conversion of degrees to integers', () {
+    csvLinesFromFile('encoding.csv').forEach(checkLocationToIntegers);
   });
 
   test('MaxCodeLength', () {