Brian Wilkerson
a0487f0f90
Change-Id: I2db2a7e3af6841ecc565c57a82bceac7bd892d4d Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/132454 Reviewed-by: Konstantin Shcheglov <scheglov@google.com> Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
56 lines
2.0 KiB
Dart
56 lines
2.0 KiB
Dart
// Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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/// Jenkins hash function, optimized for small integers.
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///
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/// Static methods borrowed from sdk/lib/math/jenkins_smi_hash.dart. Non-static
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/// methods are an enhancement for the "front_end" package.
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///
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/// Where performance is critical, use [hash2], [hash3], or [hash4], or the
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/// pattern `finish(combine(combine(...combine(0, a), b)..., z))`, where a..z
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/// are hash codes to be combined.
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///
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/// For ease of use, you may also use this pattern:
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/// `(new JenkinsSmiHash()..add(a)..add(b)....add(z)).hashCode`, where a..z are
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/// the sub-objects whose hashes should be combined. This pattern performs the
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/// same operations as the performance critical variant, but allocates an extra
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/// object.
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class JenkinsSmiHash {
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/// Accumulates the hash code [value] into the running hash [hash].
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static int combine(int hash, int value) {
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hash = 0x1fffffff & (hash + value);
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hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
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return hash ^ (hash >> 6);
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}
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/// Finalizes a running hash produced by [combine].
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static int finish(int hash) {
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hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3));
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hash = hash ^ (hash >> 11);
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return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
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}
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/// Combines together two hash codes.
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static int hash2(int a, int b) => finish(combine(combine(0, a), b));
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/// Combines together three hash codes.
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static int hash3(int a, int b, int c) =>
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finish(combine(combine(combine(0, a), b), c));
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/// Combines together four hash codes.
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static int hash4(int a, int b, int c, int d) =>
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finish(combine(combine(combine(combine(0, a), b), c), d));
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int _hash = 0;
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/// Accumulates the object [o] into the hash.
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void add(Object o) {
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_hash = combine(_hash, o.hashCode);
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}
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/// Finalizes the hash and return the resulting hashcode.
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@override
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int get hashCode => finish(_hash);
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}
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