492 lines
12 KiB
JavaScript
492 lines
12 KiB
JavaScript
/**
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* This code is mostly from the old Etherpad. Please help us to comment this code.
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* This helps other people to understand this code better and helps them to improve it.
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* TL;DR COMMENTS ON THIS FILE ARE HIGHLY APPRECIATED
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*/
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/**
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* Copyright 2009 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS-IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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function newSkipList()
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{
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var PROFILER = window.PROFILER;
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if (!PROFILER)
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{
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PROFILER = function()
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{
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return {
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start: noop,
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mark: noop,
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literal: noop,
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end: noop,
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cancel: noop
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};
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};
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}
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function noop()
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{}
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// if there are N elements in the skiplist, "start" is element -1 and "end" is element N
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var start = {
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key: null,
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levels: 1,
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upPtrs: [null],
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downPtrs: [null],
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downSkips: [1],
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downSkipWidths: [0]
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};
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var end = {
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key: null,
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levels: 1,
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upPtrs: [null],
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downPtrs: [null],
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downSkips: [null],
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downSkipWidths: [null]
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};
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var numNodes = 0;
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var totalWidth = 0;
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var keyToNodeMap = {};
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start.downPtrs[0] = end;
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end.upPtrs[0] = start;
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// a "point" object at location x allows modifications immediately after the first
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// x elements of the skiplist, such as multiple inserts or deletes.
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// After an insert or delete using point P, the point is still valid and points
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// to the same index in the skiplist. Other operations with other points invalidate
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// this point.
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function _getPoint(targetLoc)
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{
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var numLevels = start.levels;
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var lvl = numLevels - 1;
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var i = -1,
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ws = 0;
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var nodes = new Array(numLevels);
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var idxs = new Array(numLevels);
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var widthSkips = new Array(numLevels);
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nodes[lvl] = start;
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idxs[lvl] = -1;
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widthSkips[lvl] = 0;
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while (lvl >= 0)
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{
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var n = nodes[lvl];
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while (n.downPtrs[lvl] && (i + n.downSkips[lvl] < targetLoc))
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{
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i += n.downSkips[lvl];
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ws += n.downSkipWidths[lvl];
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n = n.downPtrs[lvl];
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}
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nodes[lvl] = n;
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idxs[lvl] = i;
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widthSkips[lvl] = ws;
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lvl--;
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if (lvl >= 0)
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{
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nodes[lvl] = n;
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}
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}
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return {
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nodes: nodes,
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idxs: idxs,
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loc: targetLoc,
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widthSkips: widthSkips,
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toString: function()
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{
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return "getPoint(" + targetLoc + ")";
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}
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};
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}
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function _getNodeAtOffset(targetOffset)
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{
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var i = 0;
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var n = start;
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var lvl = start.levels - 1;
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while (lvl >= 0 && n.downPtrs[lvl])
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{
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while (n.downPtrs[lvl] && (i + n.downSkipWidths[lvl] <= targetOffset))
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{
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i += n.downSkipWidths[lvl];
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n = n.downPtrs[lvl];
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}
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lvl--;
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}
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if (n === start) return (start.downPtrs[0] || null);
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else if (n === end) return (targetOffset == totalWidth ? (end.upPtrs[0] || null) : null);
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return n;
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}
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function _entryWidth(e)
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{
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return (e && e.width) || 0;
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}
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function _insertKeyAtPoint(point, newKey, entry)
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{
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var p = PROFILER("insertKey", false);
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var newNode = {
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key: newKey,
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levels: 0,
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upPtrs: [],
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downPtrs: [],
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downSkips: [],
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downSkipWidths: []
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};
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p.mark("donealloc");
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var pNodes = point.nodes;
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var pIdxs = point.idxs;
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var pLoc = point.loc;
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var widthLoc = point.widthSkips[0] + point.nodes[0].downSkipWidths[0];
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var newWidth = _entryWidth(entry);
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p.mark("loop1");
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while (newNode.levels == 0 || Math.random() < 0.01)
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{
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var lvl = newNode.levels;
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newNode.levels++;
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if (lvl == pNodes.length)
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{
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// assume we have just passed the end of point.nodes, and reached one level greater
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// than the skiplist currently supports
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pNodes[lvl] = start;
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pIdxs[lvl] = -1;
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start.levels++;
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end.levels++;
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start.downPtrs[lvl] = end;
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end.upPtrs[lvl] = start;
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start.downSkips[lvl] = numNodes + 1;
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start.downSkipWidths[lvl] = totalWidth;
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point.widthSkips[lvl] = 0;
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}
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var me = newNode;
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var up = pNodes[lvl];
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var down = up.downPtrs[lvl];
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var skip1 = pLoc - pIdxs[lvl];
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var skip2 = up.downSkips[lvl] + 1 - skip1;
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up.downSkips[lvl] = skip1;
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up.downPtrs[lvl] = me;
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me.downSkips[lvl] = skip2;
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me.upPtrs[lvl] = up;
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me.downPtrs[lvl] = down;
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down.upPtrs[lvl] = me;
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var widthSkip1 = widthLoc - point.widthSkips[lvl];
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var widthSkip2 = up.downSkipWidths[lvl] + newWidth - widthSkip1;
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up.downSkipWidths[lvl] = widthSkip1;
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me.downSkipWidths[lvl] = widthSkip2;
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}
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p.mark("loop2");
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p.literal(pNodes.length, "PNL");
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for (var lvl = newNode.levels; lvl < pNodes.length; lvl++)
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{
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var up = pNodes[lvl];
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up.downSkips[lvl]++;
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up.downSkipWidths[lvl] += newWidth;
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}
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p.mark("map");
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keyToNodeMap['$KEY$' + newKey] = newNode;
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numNodes++;
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totalWidth += newWidth;
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p.end();
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}
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function _getNodeAtPoint(point)
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{
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return point.nodes[0].downPtrs[0];
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}
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function _incrementPoint(point)
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{
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point.loc++;
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for (var i = 0; i < point.nodes.length; i++)
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{
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if (point.idxs[i] + point.nodes[i].downSkips[i] < point.loc)
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{
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point.idxs[i] += point.nodes[i].downSkips[i];
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point.widthSkips[i] += point.nodes[i].downSkipWidths[i];
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point.nodes[i] = point.nodes[i].downPtrs[i];
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}
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}
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}
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function _deleteKeyAtPoint(point)
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{
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var elem = point.nodes[0].downPtrs[0];
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var elemWidth = _entryWidth(elem.entry);
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for (var i = 0; i < point.nodes.length; i++)
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{
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if (i < elem.levels)
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{
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var up = elem.upPtrs[i];
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var down = elem.downPtrs[i];
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var totalSkip = up.downSkips[i] + elem.downSkips[i] - 1;
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up.downPtrs[i] = down;
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down.upPtrs[i] = up;
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up.downSkips[i] = totalSkip;
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var totalWidthSkip = up.downSkipWidths[i] + elem.downSkipWidths[i] - elemWidth;
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up.downSkipWidths[i] = totalWidthSkip;
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}
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else
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{
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var up = point.nodes[i];
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var down = up.downPtrs[i];
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up.downSkips[i]--;
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up.downSkipWidths[i] -= elemWidth;
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}
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}
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delete keyToNodeMap['$KEY$' + elem.key];
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numNodes--;
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totalWidth -= elemWidth;
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}
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function _propagateWidthChange(node)
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{
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var oldWidth = node.downSkipWidths[0];
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var newWidth = _entryWidth(node.entry);
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var widthChange = newWidth - oldWidth;
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var n = node;
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var lvl = 0;
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while (lvl < n.levels)
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{
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n.downSkipWidths[lvl] += widthChange;
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lvl++;
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while (lvl >= n.levels && n.upPtrs[lvl - 1])
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{
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n = n.upPtrs[lvl - 1];
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}
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}
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totalWidth += widthChange;
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}
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function _getNodeIndex(node, byWidth)
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{
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var dist = (byWidth ? 0 : -1);
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var n = node;
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while (n !== start)
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{
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var lvl = n.levels - 1;
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n = n.upPtrs[lvl];
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if (byWidth) dist += n.downSkipWidths[lvl];
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else dist += n.downSkips[lvl];
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}
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return dist;
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}
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/*function _debugToString() {
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var array = [start];
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while (array[array.length-1] !== end) {
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array[array.length] = array[array.length-1].downPtrs[0];
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}
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function getIndex(node) {
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if (!node) return null;
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for(var i=0;i<array.length;i++) {
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if (array[i] === node)
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return i-1;
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}
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return false;
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}
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var processedArray = map(array, function(node) {
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var x = {key:node.key, levels: node.levels, downSkips: node.downSkips,
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upPtrs: map(node.upPtrs, getIndex), downPtrs: map(node.downPtrs, getIndex),
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downSkipWidths: node.downSkipWidths};
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return x;
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});
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return map(processedArray, function (x) { return x.toSource(); }).join("\n");
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}*/
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function _getNodeByKey(key)
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{
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return keyToNodeMap['$KEY$' + key];
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}
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// Returns index of first entry such that entryFunc(entry) is truthy,
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// or length() if no such entry. Assumes all falsy entries come before
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// all truthy entries.
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function _search(entryFunc)
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{
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var low = start;
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var lvl = start.levels - 1;
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var lowIndex = -1;
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function f(node)
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{
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if (node === start) return false;
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else if (node === end) return true;
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else return entryFunc(node.entry);
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}
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while (lvl >= 0)
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{
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var nextLow = low.downPtrs[lvl];
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while (!f(nextLow))
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{
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lowIndex += low.downSkips[lvl];
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low = nextLow;
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nextLow = low.downPtrs[lvl];
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}
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lvl--;
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}
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return lowIndex + 1;
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}
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/*
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The skip-list contains "entries", JavaScript objects that each must have a unique "key" property
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that is a string.
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*/
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var self = {
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length: function()
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{
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return numNodes;
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},
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atIndex: function(i)
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{
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if (i < 0) console.warn("atIndex(" + i + ")");
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if (i >= numNodes) console.warn("atIndex(" + i + ">=" + numNodes + ")");
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return _getNodeAtPoint(_getPoint(i)).entry;
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},
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// differs from Array.splice() in that new elements are in an array, not varargs
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splice: function(start, deleteCount, newEntryArray)
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{
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if (start < 0) console.warn("splice(" + start + ", ...)");
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if (start + deleteCount > numNodes)
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{
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console.warn("splice(" + start + ", " + deleteCount + ", ...), N=" + numNodes);
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console.warn("%s %s %s", typeof start, typeof deleteCount, typeof numNodes);
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console.trace();
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}
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if (!newEntryArray) newEntryArray = [];
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var pt = _getPoint(start);
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for (var i = 0; i < deleteCount; i++)
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{
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_deleteKeyAtPoint(pt);
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}
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for (var i = (newEntryArray.length - 1); i >= 0; i--)
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{
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var entry = newEntryArray[i];
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_insertKeyAtPoint(pt, entry.key, entry);
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var node = _getNodeByKey(entry.key);
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node.entry = entry;
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}
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},
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next: function(entry)
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{
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return _getNodeByKey(entry.key).downPtrs[0].entry || null;
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},
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prev: function(entry)
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{
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return _getNodeByKey(entry.key).upPtrs[0].entry || null;
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},
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push: function(entry)
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{
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self.splice(numNodes, 0, [entry]);
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},
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slice: function(start, end)
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{
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// act like Array.slice()
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if (start === undefined) start = 0;
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else if (start < 0) start += numNodes;
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if (end === undefined) end = numNodes;
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else if (end < 0) end += numNodes;
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if (start < 0) start = 0;
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if (start > numNodes) start = numNodes;
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if (end < 0) end = 0;
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if (end > numNodes) end = numNodes;
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dmesg(String([start, end, numNodes]));
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if (end <= start) return [];
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var n = self.atIndex(start);
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var array = [n];
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for (var i = 1; i < (end - start); i++)
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{
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n = self.next(n);
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array.push(n);
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}
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return array;
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},
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atKey: function(key)
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{
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return _getNodeByKey(key).entry;
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},
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indexOfKey: function(key)
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{
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return _getNodeIndex(_getNodeByKey(key));
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},
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indexOfEntry: function(entry)
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{
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return self.indexOfKey(entry.key);
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},
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containsKey: function(key)
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{
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return !!(_getNodeByKey(key));
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},
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// gets the last entry starting at or before the offset
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atOffset: function(offset)
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{
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return _getNodeAtOffset(offset).entry;
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},
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keyAtOffset: function(offset)
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{
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return self.atOffset(offset).key;
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},
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offsetOfKey: function(key)
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{
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return _getNodeIndex(_getNodeByKey(key), true);
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},
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offsetOfEntry: function(entry)
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{
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return self.offsetOfKey(entry.key);
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},
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setEntryWidth: function(entry, width)
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{
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entry.width = width;
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_propagateWidthChange(_getNodeByKey(entry.key));
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},
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totalWidth: function()
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{
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return totalWidth;
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},
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offsetOfIndex: function(i)
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{
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if (i < 0) return 0;
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if (i >= numNodes) return totalWidth;
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return self.offsetOfEntry(self.atIndex(i));
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},
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indexOfOffset: function(offset)
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{
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if (offset <= 0) return 0;
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if (offset >= totalWidth) return numNodes;
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return self.indexOfEntry(self.atOffset(offset));
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},
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search: function(entryFunc)
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{
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return _search(entryFunc);
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},
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//debugToString: _debugToString,
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debugGetPoint: _getPoint,
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debugDepth: function()
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{
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return start.levels;
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}
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}
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return self;
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}
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exports.newSkipList = newSkipList;
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