Add more complex mixing of random seed.

tests/lib/math/random_test.dart

Index: tests/lib/math/random_test.dart
diff --git a/tests/lib/math/random_test.dart b/tests/lib/math/random_test.dart
index 28cf084714bf912fe09981aa6434e07726d8e821..f769efb793e691f69c13232324e0ad58d3b55ab2 100644
--- a/tests/lib/math/random_test.dart
+++ b/tests/lib/math/random_test.dart
@@ -11,50 +11,91 @@ import "package:expect/expect.dart";
 import 'dart:math';
 
 main() {
+  checkSequence();
+  checkSeed();
+}
+
+void checkSequence() {
+  // Check the sequence of numbers generated by the random generator for a seed
+  // doesn't change unintendedly, and it agrees between implementations.
   var rnd = new Random(20130307);
   // Make sure we do not break the random number generation.
   // If the random algorithm changes, make sure both the VM and dart2js
   // generate the same new sequence.
   var i = 1;
-  Expect.equals(         1, rnd.nextInt(i *= 2));
-  Expect.equals(         1, rnd.nextInt(i *= 2));
+  Expect.equals(         0, rnd.nextInt(i *= 2));
+  Expect.equals(         3, rnd.nextInt(i *= 2));
   Expect.equals(         7, rnd.nextInt(i *= 2));
-  Expect.equals(         6, rnd.nextInt(i *= 2));
-  Expect.equals(         6, rnd.nextInt(i *= 2));
-  Expect.equals(        59, rnd.nextInt(i *= 2));
-  Expect.equals(        11, rnd.nextInt(i *= 2));
-  Expect.equals(       212, rnd.nextInt(i *= 2));
+  Expect.equals(         5, rnd.nextInt(i *= 2));
+  Expect.equals(        29, rnd.nextInt(i *= 2));
   Expect.equals(        17, rnd.nextInt(i *= 2));
-  Expect.equals(       507, rnd.nextInt(i *= 2));
-  Expect.equals(      1060, rnd.nextInt(i *= 2));
-  Expect.equals(       891, rnd.nextInt(i *= 2));
-  Expect.equals(      1534, rnd.nextInt(i *= 2));
-  Expect.equals(      8404, rnd.nextInt(i *= 2));
-  Expect.equals(     13839, rnd.nextInt(i *= 2));
-  Expect.equals(     23298, rnd.nextInt(i *= 2));
-  Expect.equals(     53622, rnd.nextInt(i *= 2));
-  Expect.equals(    205997, rnd.nextInt(i *= 2));
-  Expect.equals(    393823, rnd.nextInt(i *= 2));
-  Expect.equals(    514614, rnd.nextInt(i *= 2));
-  Expect.equals(    233715, rnd.nextInt(i *= 2));
-  Expect.equals(    895357, rnd.nextInt(i *= 2));
-  Expect.equals(   4726185, rnd.nextInt(i *= 2));
-  Expect.equals(   7976427, rnd.nextInt(i *= 2));
-  Expect.equals(  31792146, rnd.nextInt(i *= 2));
-  Expect.equals(  35563210, rnd.nextInt(i *= 2));
-  Expect.equals( 113261265, rnd.nextInt(i *= 2));
-  Expect.equals( 205117298, rnd.nextInt(i *= 2));
-  Expect.equals( 447729735, rnd.nextInt(i *= 2));
-  Expect.equals(1072507596, rnd.nextInt(i *= 2));
-  Expect.equals(2134030067, rnd.nextInt(i *= 2));
-  Expect.equals( 721180690, rnd.nextInt(i *= 2));
+  Expect.equals(       104, rnd.nextInt(i *= 2));
+  Expect.equals(       199, rnd.nextInt(i *= 2));
+  Expect.equals(       408, rnd.nextInt(i *= 2));
+  Expect.equals(       362, rnd.nextInt(i *= 2));
+  Expect.equals(       995, rnd.nextInt(i *= 2));
+  Expect.equals(      2561, rnd.nextInt(i *= 2));
+  Expect.equals(      2548, rnd.nextInt(i *= 2));
+  Expect.equals(      9553, rnd.nextInt(i *= 2));
+  Expect.equals(      2628, rnd.nextInt(i *= 2));
+  Expect.equals(     42376, rnd.nextInt(i *= 2));
+  Expect.equals(    101848, rnd.nextInt(i *= 2));
+  Expect.equals(     85153, rnd.nextInt(i *= 2));
+  Expect.equals(    495595, rnd.nextInt(i *= 2));
+  Expect.equals(    647122, rnd.nextInt(i *= 2));
+  Expect.equals(    793546, rnd.nextInt(i *= 2));
+  Expect.equals(   1073343, rnd.nextInt(i *= 2));
+  Expect.equals(   4479969, rnd.nextInt(i *= 2));
+  Expect.equals(   9680425, rnd.nextInt(i *= 2));
+  Expect.equals(  28460171, rnd.nextInt(i *= 2));
+  Expect.equals(  49481738, rnd.nextInt(i *= 2));
+  Expect.equals(   9878974, rnd.nextInt(i *= 2));
+  Expect.equals( 132552472, rnd.nextInt(i *= 2));
+  Expect.equals( 210267283, rnd.nextInt(i *= 2));
+  Expect.equals( 125422442, rnd.nextInt(i *= 2));
+  Expect.equals( 226275094, rnd.nextInt(i *= 2));
+  Expect.equals(1639629168, rnd.nextInt(i *= 2));
   Expect.equals(0x100000000, i);
   // If max is too large expect an ArgumentError.
   Expect.throws(() => rnd.nextInt(i + 1), (e) => e is ArgumentError);
 
   rnd = new Random(6790);
-  Expect.approxEquals(0.7360144236, rnd.nextDouble());
-  Expect.approxEquals(0.3292339731, rnd.nextDouble());
-  Expect.approxEquals(0.3489622548, rnd.nextDouble());
-  Expect.approxEquals(0.9815975892, rnd.nextDouble());
+  Expect.approxEquals(0.1202733131, rnd.nextDouble());
+  Expect.approxEquals(0.5554054805, rnd.nextDouble());
+  Expect.approxEquals(0.0385160727, rnd.nextDouble());
+  Expect.approxEquals(0.2836345217, rnd.nextDouble());
+}
+
+void checkSeed() {
+  // Check that various seeds generate the expected first values.
+  // 53 significant bits, so the number is representable in JS.
+  var rawSeed = 0x19a32c640e1d71;
+  var expectations = [
+    26007, 43006, 46458, 18610, 16413, 50455,  2164, 47399,  8859,  9732,
+    20367, 33935, 54549, 54913,  4819, 24198, 49353, 22277, 51852, 35959,
+    45347, 12100, 10136, 22372, 15293, 20066,  1351, 49030, 64845, 12793,
+    50916, 55784, 43170, 27653, 34696,  1492, 50255,  9597, 45929,  2874,
+    27629, 53084, 36064, 42140, 32016, 41751, 13967, 20516,   578, 16773,
+    53064, 14814, 22737, 48846, 45147, 10205, 56584, 63711, 44128, 21099,
+    47966, 35471, 39576,  1141, 45716, 54940, 57406, 15437, 31721, 35044,
+    28136, 39797, 50801, 22184, 58686
+  ];
+  var negative_seed_expectations = [
+    12170, 42844, 39228, 64032, 29046, 57572,  8453, 52224, 27060, 28454,
+    20510, 28804, 59221, 53422, 11047, 50864, 33997, 19611,  1250, 65088,
+    19690, 11396,    20, 48867, 44862, 47129, 58724, 13325, 50005, 33320,
+    16523,  4740, 63721, 63272, 30545, 51403, 35845,  3943, 31850, 23148,
+    26307,  1724, 29281, 39988, 43653, 48012, 43810, 16755, 13105, 25325,
+    32648, 19958, 38838,  8322,  3421, 28624, 17269, 45385, 50680,  1696,
+    26088,  2787, 48566, 34357, 27731, 51764,  8455, 16498, 59721, 59568,
+    46333,  7935, 51459, 36766, 50711
+  ];
+  for (var i = 0, m = 1; i < 75; i++) {
+    Expect.equals(expectations[i], new Random(rawSeed * m).nextInt(65536));
+    Expect.equals(negative_seed_expectations[i],
+                  new Random(rawSeed * -m).nextInt(65536));
+    m *= 2;
+  }
+  // And test zero seed too.
+  Expect.equals(21391, new Random(0).nextInt(65536));
 }