public-offering
/
pad.pub0.org
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

skiplist: Convert point operations into `Point` methods

pull/5003/head
Richard Hansen 2021-04-11 21:11:30 -04:00
parent 3c1be95e07
commit 9fc88f3601
1 changed files with 91 additions and 90 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

181
src/static/js/skiplist.js
View File

@ -23,7 +23,6 @@
*/
const _entryWidth = (e) => (e && e.width) || 0;
const _getNodeAtPoint = (point) => point.nodes[0].downPtrs[0];
// A "point" object at index x allows modifications immediately after the first x elements of the
// skiplist, such as multiple inserts or deletes. After an insert or delete using point P, the point
@ -66,6 +65,94 @@ class Point {
toString() {
return `Point(${this.loc})`;
}
insert(entry) {
const newNode = {
key: entry.key,
entry,
levels: 0,
upPtrs: [],
downPtrs: [],
downSkips: [],
downSkipWidths: [],
};
const pNodes = this.nodes;
const pIdxs = this.idxs;
const pLoc = this.loc;
const widthLoc = this.widthSkips[0] + this.nodes[0].downSkipWidths[0];
const newWidth = _entryWidth(entry);
// The new node will have at least level 1
// With a proability of 0.01^(n-1) the nodes level will be >= n
while (newNode.levels === 0 || Math.random() < 0.01) {
const lvl = newNode.levels;
newNode.levels++;
if (lvl === pNodes.length) {
// assume we have just passed the end of this.nodes, and reached one level greater
// than the skiplist currently supports
pNodes[lvl] = this._skipList._start;
pIdxs[lvl] = -1;
this._skipList._start.levels++;
this._skipList._end.levels++;
this._skipList._start.downPtrs[lvl] = this._skipList._end;
this._skipList._end.upPtrs[lvl] = this._skipList._start;
this._skipList._start.downSkips[lvl] = this._skipList._numNodes + 1;
this._skipList._start.downSkipWidths[lvl] = this._skipList._totalWidth;
this.widthSkips[lvl] = 0;
}
const me = newNode;
const up = pNodes[lvl];
const down = up.downPtrs[lvl];
const skip1 = pLoc - pIdxs[lvl];
const skip2 = up.downSkips[lvl] + 1 - skip1;
up.downSkips[lvl] = skip1;
up.downPtrs[lvl] = me;
me.downSkips[lvl] = skip2;
me.upPtrs[lvl] = up;
me.downPtrs[lvl] = down;
down.upPtrs[lvl] = me;
const widthSkip1 = widthLoc - this.widthSkips[lvl];
const widthSkip2 = up.downSkipWidths[lvl] + newWidth - widthSkip1;
up.downSkipWidths[lvl] = widthSkip1;
me.downSkipWidths[lvl] = widthSkip2;
}
for (let lvl = newNode.levels; lvl < pNodes.length; lvl++) {
const up = pNodes[lvl];
up.downSkips[lvl]++;
up.downSkipWidths[lvl] += newWidth;
}
this._skipList._keyToNodeMap[`$KEY$${newNode.key}`] = newNode;
this._skipList._numNodes++;
this._skipList._totalWidth += newWidth;
}
delete() {
const elem = this.nodes[0].downPtrs[0];
const elemWidth = _entryWidth(elem.entry);
for (let i = 0; i < this.nodes.length; i++) {
if (i < elem.levels) {
const up = elem.upPtrs[i];
const down = elem.downPtrs[i];
const totalSkip = up.downSkips[i] + elem.downSkips[i] - 1;
up.downPtrs[i] = down;
down.upPtrs[i] = up;
up.downSkips[i] = totalSkip;
const totalWidthSkip = up.downSkipWidths[i] + elem.downSkipWidths[i] - elemWidth;
up.downSkipWidths[i] = totalWidthSkip;
} else {
const up = this.nodes[i];
up.downSkips[i]--;
up.downSkipWidths[i] -= elemWidth;
}
}
delete this._skipList._keyToNodeMap[`$KEY$${elem.key}`];
this._skipList._numNodes--;
this._skipList._totalWidth -= elemWidth;
}
getNode() {
return this.nodes[0].downPtrs[0];
}
}
/**
@ -116,90 +203,6 @@ class SkipList {
return n;
}
_insertKeyAtPoint(point, entry) {
const newNode = {
key: entry.key,
entry,
levels: 0,
upPtrs: [],
downPtrs: [],
downSkips: [],
downSkipWidths: [],
};
const pNodes = point.nodes;
const pIdxs = point.idxs;
const pLoc = point.loc;
const widthLoc = point.widthSkips[0] + point.nodes[0].downSkipWidths[0];
const newWidth = _entryWidth(entry);
// The new node will have at least level 1
// With a proability of 0.01^(n-1) the nodes level will be >= n
while (newNode.levels === 0 || Math.random() < 0.01) {
const lvl = newNode.levels;
newNode.levels++;
if (lvl === pNodes.length) {
// assume we have just passed the end of point.nodes, and reached one level greater
// than the skiplist currently supports
pNodes[lvl] = this._start;
pIdxs[lvl] = -1;
this._start.levels++;
this._end.levels++;
this._start.downPtrs[lvl] = this._end;
this._end.upPtrs[lvl] = this._start;
this._start.downSkips[lvl] = this._numNodes + 1;
this._start.downSkipWidths[lvl] = this._totalWidth;
point.widthSkips[lvl] = 0;
}
const me = newNode;
const up = pNodes[lvl];
const down = up.downPtrs[lvl];
const skip1 = pLoc - pIdxs[lvl];
const skip2 = up.downSkips[lvl] + 1 - skip1;
up.downSkips[lvl] = skip1;
up.downPtrs[lvl] = me;
me.downSkips[lvl] = skip2;
me.upPtrs[lvl] = up;
me.downPtrs[lvl] = down;
down.upPtrs[lvl] = me;
const widthSkip1 = widthLoc - point.widthSkips[lvl];
const widthSkip2 = up.downSkipWidths[lvl] + newWidth - widthSkip1;
up.downSkipWidths[lvl] = widthSkip1;
me.downSkipWidths[lvl] = widthSkip2;
}
for (let lvl = newNode.levels; lvl < pNodes.length; lvl++) {
const up = pNodes[lvl];
up.downSkips[lvl]++;
up.downSkipWidths[lvl] += newWidth;
}
this._keyToNodeMap[`$KEY$${newNode.key}`] = newNode;
this._numNodes++;
this._totalWidth += newWidth;
}
_deleteKeyAtPoint(point) {
const elem = point.nodes[0].downPtrs[0];
const elemWidth = _entryWidth(elem.entry);
for (let i = 0; i < point.nodes.length; i++) {
if (i < elem.levels) {
const up = elem.upPtrs[i];
const down = elem.downPtrs[i];
const totalSkip = up.downSkips[i] + elem.downSkips[i] - 1;
up.downPtrs[i] = down;
down.upPtrs[i] = up;
up.downSkips[i] = totalSkip;
const totalWidthSkip = up.downSkipWidths[i] + elem.downSkipWidths[i] - elemWidth;
up.downSkipWidths[i] = totalWidthSkip;
} else {
const up = point.nodes[i];
up.downSkips[i]--;
up.downSkipWidths[i] -= elemWidth;
}
}
delete this._keyToNodeMap[`$KEY$${elem.key}`];
this._numNodes--;
this._totalWidth -= elemWidth;
}
_propagateWidthChange(node) {
const oldWidth = node.downSkipWidths[0];
const newWidth = _entryWidth(node.entry);
@ -261,7 +264,7 @@ class SkipList {
atIndex(i) {
if (i < 0) console.warn(`atIndex(${i})`);
if (i >= this._numNodes) console.warn(`atIndex(${i}>=${this._numNodes})`);
return _getNodeAtPoint(new Point(this, i)).entry;
return (new Point(this, i)).getNode().entry;
}
// differs from Array.splice() in that new elements are in an array, not varargs
@ -275,12 +278,10 @@ class SkipList {
if (!newEntryArray) newEntryArray = [];
const pt = new Point(this, start);
for (let i = 0; i < deleteCount; i++) {
this._deleteKeyAtPoint(pt);
}
for (let i = 0; i < deleteCount; i++) pt.delete();
for (let i = (newEntryArray.length - 1); i >= 0; i--) {
const entry = newEntryArray[i];
this._insertKeyAtPoint(pt, entry);
pt.insert(entry);
}
}