skiplist: Convert point operations into `Point` methods
Richard Hansen
parent
3c1be95e07
commit
9fc88f3601
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@ -23,7 +23,6 @@
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*/
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*/
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const _entryWidth = (e) => (e && e.width) || 0;
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const _entryWidth = (e) => (e && e.width) || 0;
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const _getNodeAtPoint = (point) => point.nodes[0].downPtrs[0];
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// A "point" object at index x allows modifications immediately after the first x elements of the
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// A "point" object at index x allows modifications immediately after the first x elements of the
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// skiplist, such as multiple inserts or deletes. After an insert or delete using point P, the point
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// skiplist, such as multiple inserts or deletes. After an insert or delete using point P, the point
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@ -66,6 +65,94 @@ class Point {
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toString() {
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toString() {
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return `Point(${this.loc})`;
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return `Point(${this.loc})`;
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}
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}
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insert(entry) {
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const newNode = {
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key: entry.key,
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entry,
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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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const pNodes = this.nodes;
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const pIdxs = this.idxs;
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const pLoc = this.loc;
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const widthLoc = this.widthSkips[0] + this.nodes[0].downSkipWidths[0];
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const newWidth = _entryWidth(entry);
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// The new node will have at least level 1
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// With a proability of 0.01^(n-1) the nodes level will be >= n
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while (newNode.levels === 0 || Math.random() < 0.01) {
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const lvl = newNode.levels;
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newNode.levels++;
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if (lvl === pNodes.length) {
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// assume we have just passed the end of this.nodes, and reached one level greater
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// than the skiplist currently supports
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pNodes[lvl] = this._skipList._start;
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pIdxs[lvl] = -1;
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this._skipList._start.levels++;
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this._skipList._end.levels++;
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this._skipList._start.downPtrs[lvl] = this._skipList._end;
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this._skipList._end.upPtrs[lvl] = this._skipList._start;
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this._skipList._start.downSkips[lvl] = this._skipList._numNodes + 1;
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this._skipList._start.downSkipWidths[lvl] = this._skipList._totalWidth;
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this.widthSkips[lvl] = 0;
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}
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const me = newNode;
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const up = pNodes[lvl];
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const down = up.downPtrs[lvl];
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const skip1 = pLoc - pIdxs[lvl];
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const 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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const widthSkip1 = widthLoc - this.widthSkips[lvl];
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const 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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for (let lvl = newNode.levels; lvl < pNodes.length; lvl++) {
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const 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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this._skipList._keyToNodeMap[`$KEY$${newNode.key}`] = newNode;
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this._skipList._numNodes++;
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this._skipList._totalWidth += newWidth;
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}
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delete() {
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const elem = this.nodes[0].downPtrs[0];
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const elemWidth = _entryWidth(elem.entry);
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for (let i = 0; i < this.nodes.length; i++) {
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if (i < elem.levels) {
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const up = elem.upPtrs[i];
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const down = elem.downPtrs[i];
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const totalSkip = up.downSkips[i] + elem.downSkips[i] - 1;
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up.downPtrs[i] = down;
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down.upPtrs[i] = up;
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up.downSkips[i] = totalSkip;
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const totalWidthSkip = up.downSkipWidths[i] + elem.downSkipWidths[i] - elemWidth;
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up.downSkipWidths[i] = totalWidthSkip;
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} else {
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const up = this.nodes[i];
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up.downSkips[i]--;
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up.downSkipWidths[i] -= elemWidth;
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}
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}
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delete this._skipList._keyToNodeMap[`$KEY$${elem.key}`];
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this._skipList._numNodes--;
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this._skipList._totalWidth -= elemWidth;
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}
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getNode() {
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return this.nodes[0].downPtrs[0];
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}
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}
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}
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/**
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/**
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@ -116,90 +203,6 @@ class SkipList {
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return n;
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return n;
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}
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}
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_insertKeyAtPoint(point, entry) {
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const newNode = {
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key: entry.key,
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entry,
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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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const pNodes = point.nodes;
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const pIdxs = point.idxs;
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const pLoc = point.loc;
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const widthLoc = point.widthSkips[0] + point.nodes[0].downSkipWidths[0];
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const newWidth = _entryWidth(entry);
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// The new node will have at least level 1
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// With a proability of 0.01^(n-1) the nodes level will be >= n
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while (newNode.levels === 0 || Math.random() < 0.01) {
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const lvl = newNode.levels;
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newNode.levels++;
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if (lvl === pNodes.length) {
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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] = this._start;
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pIdxs[lvl] = -1;
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this._start.levels++;
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this._end.levels++;
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this._start.downPtrs[lvl] = this._end;
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this._end.upPtrs[lvl] = this._start;
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this._start.downSkips[lvl] = this._numNodes + 1;
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this._start.downSkipWidths[lvl] = this._totalWidth;
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point.widthSkips[lvl] = 0;
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}
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const me = newNode;
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const up = pNodes[lvl];
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const down = up.downPtrs[lvl];
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const skip1 = pLoc - pIdxs[lvl];
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const 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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const widthSkip1 = widthLoc - point.widthSkips[lvl];
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const 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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for (let lvl = newNode.levels; lvl < pNodes.length; lvl++) {
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const 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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this._keyToNodeMap[`$KEY$${newNode.key}`] = newNode;
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this._numNodes++;
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this._totalWidth += newWidth;
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}
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_deleteKeyAtPoint(point) {
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const elem = point.nodes[0].downPtrs[0];
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const elemWidth = _entryWidth(elem.entry);
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for (let i = 0; i < point.nodes.length; i++) {
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if (i < elem.levels) {
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const up = elem.upPtrs[i];
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const down = elem.downPtrs[i];
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const totalSkip = up.downSkips[i] + elem.downSkips[i] - 1;
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up.downPtrs[i] = down;
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down.upPtrs[i] = up;
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up.downSkips[i] = totalSkip;
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const totalWidthSkip = up.downSkipWidths[i] + elem.downSkipWidths[i] - elemWidth;
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up.downSkipWidths[i] = totalWidthSkip;
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} else {
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const up = point.nodes[i];
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up.downSkips[i]--;
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up.downSkipWidths[i] -= elemWidth;
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}
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}
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delete this._keyToNodeMap[`$KEY$${elem.key}`];
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this._numNodes--;
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this._totalWidth -= elemWidth;
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}
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_propagateWidthChange(node) {
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_propagateWidthChange(node) {
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const oldWidth = node.downSkipWidths[0];
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const oldWidth = node.downSkipWidths[0];
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const newWidth = _entryWidth(node.entry);
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const newWidth = _entryWidth(node.entry);
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@ -261,7 +264,7 @@ class SkipList {
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atIndex(i) {
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atIndex(i) {
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if (i < 0) console.warn(`atIndex(${i})`);
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if (i < 0) console.warn(`atIndex(${i})`);
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if (i >= this._numNodes) console.warn(`atIndex(${i}>=${this._numNodes})`);
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if (i >= this._numNodes) console.warn(`atIndex(${i}>=${this._numNodes})`);
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return _getNodeAtPoint(new Point(this, i)).entry;
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return (new Point(this, i)).getNode().entry;
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}
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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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// differs from Array.splice() in that new elements are in an array, not varargs
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@ -275,12 +278,10 @@ class SkipList {
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if (!newEntryArray) newEntryArray = [];
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if (!newEntryArray) newEntryArray = [];
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const pt = new Point(this, start);
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const pt = new Point(this, start);
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for (let i = 0; i < deleteCount; i++) {
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for (let i = 0; i < deleteCount; i++) pt.delete();
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this._deleteKeyAtPoint(pt);
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}
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for (let i = (newEntryArray.length - 1); i >= 0; i--) {
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for (let i = (newEntryArray.length - 1); i >= 0; i--) {
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const entry = newEntryArray[i];
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const entry = newEntryArray[i];
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this._insertKeyAtPoint(pt, entry);
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pt.insert(entry);
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}
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}
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}
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}
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