Index: lib/math/random.dart |
=================================================================== |
--- lib/math/random.dart (revision 0) |
+++ lib/math/random.dart (revision 0) |
@@ -0,0 +1,109 @@ |
+// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file |
+// for details. All rights reserved. Use of this source code is governed by a |
+// BSD-style license that can be found in the LICENSE file. |
+ |
+// A part of the dart:math library. |
+ |
+/** |
+ * A random number generator. The default implementation supplies a stream of |
+ * pseudo-random bits which is not suitable for cryptographic purposes. |
+ */ |
+interface Random default _Random { |
+ /** |
+ * Creates a random-number generator. The optional parameter [seed] is used |
+ * to initialize the internal state of the generator. The implementation of |
+ * the random stream can change between releases of the library. |
+ * |
+ * Implementation note: The default implementation uses up to 64-bits of seed. |
+ */ |
+ Random([int seed]); |
+ |
+ /** |
+ * Generates a positive random integer uniformly distributed on the range |
+ * from 0, inclusive, to [max], exclusive. |
+ * |
+ * Implementation note: The default implementation supports [max] values |
+ * between 1 and ((1<<32) - 1) inclusive. |
+ */ |
+ int nextInt(int max); |
+ |
+ /** |
+ * Generates a positive random floating point value uniformly distributed on |
+ * the range from 0.0, inclusive, to 1.0, exclusive. |
+ */ |
+ double nextDouble(); |
+ |
+ /** |
+ * Generates a random boolean value. |
+ */ |
+ bool nextBool(); |
+} |
+ |
+class _Random implements Random { |
+ |
+ _Random([int seed = null]) { |
+ if (seed == null) { |
+ seed = _nextSeed(); |
+ } |
+ do { |
+ seed = (seed + 0x5A17) & _MASK_64; |
+ } while (seed == 0); |
+ _state = seed; |
+ } |
+ |
+ // The algorithm used here is Multiply with Carry (MWC) with a Base b = 2^32. |
+ // http://en.wikipedia.org/wiki/Multiply-with-carry |
+ // The constant A is selected from "Numerical Recipes 3rd Edition" p.348 B1. |
+ int _nextInt32() { |
+ _state = ((_A * (_state & _MASK_32)) + (_state >> 32)) & _MASK_64; |
+ return _state & _MASK_32; |
+ } |
+ |
+ int nextInt(int max) { |
+ if (max <= 0 || max > _POW2_32) { |
+ throw new IllegalArgumentException("max must be positive and < 2^32:" |
+ " $max"); |
+ } |
+ if ((max & -max) == max) { |
+ // Fast case for powers of two. |
+ return _nextInt32() & (max - 1); |
+ } |
+ |
+ var rnd32; |
+ var result; |
+ do { |
+ rnd32 = _nextInt32(); |
+ result = rnd32 % max; |
+ } while (rnd32 - result + max >= _POW2_32); |
+ return result; |
+ } |
+ |
+ double nextDouble() { |
+ return ((nextInt(1 << (26)) << 27) + nextInt(1 << 27)) / _POW2_53_D; |
+ } |
+ |
+ bool nextBool() { |
+ return nextInt(1) == 0; |
+ } |
+ |
+ static final _MASK_32 = (1 << 32) - 1; |
+ static final _MASK_64 = (1 << 64) - 1; |
+ static final _POW2_32 = 1 << 32; |
+ static final _POW2_53_D = 1.0 * (1 << 53); |
+ |
+ static final _A = 0xffffda61; |
+ |
+ var _state; |
+ |
+ int _nextSeed() { |
+ if (_prng == null) { |
+ // TODO(iposva): Use system to get a random seed. |
+ _prng = new _Random(new Date.now().value); |
+ } |
+ // Trigger the PRNG once to change the internal state. |
+ _prng._nextInt32(); |
+ return _prng._state; |
+ } |
+ |
+ static var _prng = null; |
+} |