Move scanner tests into the front_end package.

pkg/front_end/lib/src/base/jenkins_smi_hash.dart

+// Copyright (c) 2016, 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.
+
+/// Jenkins hash function, optimized for small integers.
+/// Borrowed from sdk/lib/math/jenkins_smi_hash.dart.

[Brian Wilkerson, 2016/11/15 20:51:37]

"Borrowed from sdk/lib/math/jenkins_smi_hash.dart" --> "Originally borrowed from
sdk/lib/math/jenkins_smi_hash.dart. Enhanced with ..."

[Paul Berry, 2016/11/15 22:54:23]

Done.

+///
+/// Where performance is critical, use [hash2], [hash3], or [hash4], or the
+/// pattern `finish(combine(combine(...combine(0, a), b)..., z))`, where a..z
+/// are hash codes to be combined.
+///
+/// For ease of use, you may also use this pattern:
+/// `(new JenkinsSmiHash()..add(a)..add(b)....add(z)).hashCode`, where a..z are
+/// the sub-objects whose hashes should be combined.  This pattern performs the
+/// same operations as the performance critical variant, but allocates an extra
+/// object.
+class JenkinsSmiHash {
+  /// Accumulates the hash code [value] into the running hash [hash].
+  static int combine(int hash, int value) {
+    hash = 0x1fffffff & (hash + value);
+    hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
+    return hash ^ (hash >> 6);
+  }
+
+  /// Finalizes a running hash produced by [combine].
+  static int finish(int hash) {
+    hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3));
+    hash = hash ^ (hash >> 11);
+    return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
+  }
+
+  /// Combines together two hash codes.
+  static int hash2(a, b) => finish(combine(combine(0, a), b));
+
+  /// Combines together three hash codes.
+  static int hash3(a, b, c) => finish(combine(combine(combine(0, a), b), c));
+
+  /// Combines together four hash codes.
+  static int hash4(a, b, c, d) =>
+      finish(combine(combine(combine(combine(0, a), b), c), d));
+
+  int _hash = 0;
+
+  /// Accumulates the object [o] into the hash.
+  void add(Object o) {
+    _hash = combine(_hash, o.hashCode);
+  }
+
+  /// Finalizes the hash and return the resulting hashcode.
+  int get hashCode => finish(_hash);
+}