sdk/lib/math/jenkins_smi_hash.dart

// Copyright (c) 2013, 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.

part of dart.math;

/// This is the [Jenkins hash function][1] but using masking to keep
/// values in SMI range.
///
/// [1]: http://en.wikipedia.org/wiki/Jenkins_hash_function
///
/// Use:
/// Hash each value with the hash of the previous value, then get the final
/// hash by calling finish.
///
///     var hash = 0;
///     for (var value in values) {
///       hash = JenkinsSmiHash.combine(hash, value.hashCode);
///     }
///     hash = JenkinsSmiHash.finish(hash);
class _JenkinsSmiHash {
  // TODO(11617): This class should be optimized and standardized elsewhere.

  static int combine(int hash, int value) {
    hash = 0x1fffffff & (hash + value);
    hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
    return hash ^ (hash >> 6);
  }

  static int finish(int hash) {
    hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3));
    hash = hash ^ (hash >> 11);
    return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
  }

  static int hash2(int a, int b) => finish(combine(combine(0, a), b));

  static int hash4(int a, int b, int c, int d) =>
      finish(combine(combine(combine(combine(0, a), b), c), d));
}