Revert: StringCanonicalizer for Fasta

pkg/front_end/lib/src/fasta/scanner/canonicalizer.dart

-// Copyright (c) 2017, 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.
-
-library fasta.scanner.abstract_scanner;
-
-import 'dart:convert';
-
-class Node {
-  var /* String | List<int> */ data; 
-  int start;
-  int end;
-  String payload;
-  Node next;
-  Node(this.data, this.start, this.end, this.payload, this.next);
-}
-
-/**
- * A hash table for triples:
- *  (list of bytes, start, end) --> canonicalized string
- * Using triples avoids allocating string slices before checking if they
- * are canonical.
- * 
- * Gives about 3% speedup on dart2js.
- */
-class StringCanonicalizer {
-  /// Mask away top bits to keep hash calculation within 32-bit SMI range.
-  static const int MASK = 16 * 1024 * 1024 - 1;
-
-  static const int INITIAL_SIZE = 8 * 1024;
-
-  /// Linear size of a hash table.
-  int _size = INITIAL_SIZE;
-  /// Items in a hash table.
-  int _count = 0;
-  /// The table itself.
-  Node _nodes = new List<Node>(INITIAL_SIZE);
-
-  static String decode(List<int> data, int start, int end, bool asciiOnly) {
-    var s;
-    if (asciiOnly) {
-      s = new String.fromCharCodes(data, start, end);
-    } else {
-      s = new Utf8Decoder(allowMalformed: true).convert(data, start, end);
-    }
-    return s;
-  }
-
-  static int hashBytes(List<int> data, int start, int end) {
-    int h = 5381;
-    for (int i = start; i < end; i++) {
-      h = ((h << 5) + h + data[i]) & MASK;
-    }
-    return h;
-  }
-
-  static int hashString(String data, int start, int end) {
-    int h = 5381;
-    for (int i = start; i < end; i++) {
-      h = ((h << 5) + h + data.codeUnitAt(i)) & MASK;
-    }
-    return h;
-  }
-
-  rehash() {
-    var newSize = _size * 2;
-    var newNodes = new List<Node>(newSize);
-    for (int i = 0; i < _size; i++) {
-      Node t = _nodes[i];
-      while (t != null) {
-        Node n = t.next;
-        int newIndex = hashBytes(t.data, t.start, t.end) & (newSize - 1);
-        Node s = newNodes[newIndex];
-        t.next = s;
-        newNodes[newIndex] = t;
-        t = n;
-      }
-    }
-    _size = newSize;
-    _nodes = newNodes;
-  }
-
-  String canonicalize(data, int start, int end, bool asciiOnly) {
-    if (_count > _size) rehash();
-    int index = data is String
-        ? hashString(data, start, end)
-        : hashBytes(data, start, end);
-    index = index & (_size - 1);
-    Node s = _nodes[index];
-    Node t = s;
-    int len = end - start;
-    while (t != null) {
-      if (t.end - t.start == len) {
-        int i = start, j = t.start;
-        while (i < end && data[i] == t.data[j]) {
-          i++;
-          j++;
-        }
-        if (i == end) {
-          return t.payload;
-        }
-      }
-      t = t.next;
-    }
-    String payload;
-    if (data is String)
-      payload = data.substring(start, end);
-    else
-      payload = decode(data, start, end, asciiOnly);
-    _nodes[index] = new Node(data, start, end, payload, s);
-    _count++;
-    return payload;
-  }
-
-  clear() {
-    _nodes = new List<Node>(_size);
-  }
-}