Replace _mappings array with data structure

Optimized for best case (called with sorted mappings), with comparable performance otherwise.

Author: crisptrutski

lib/source-map/mapping-list.js

@@ -0,0 +1,80 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
+/*
+ * Copyright 2014 Mozilla Foundation and contributors
+ * Licensed under the New BSD license. See LICENSE or:
+ * http://opensource.org/licenses/BSD-3-Clause
+ */
+if (typeof define !== 'function') {
+ var define = require('amdefine')(module, require);
+}
+define(function (require, exports, module) {
+
+ var util = require('./util');
+
+ /**
+ * Determine whether mappingB is after mappingA with respect to generated 
+ * position.
+ */
+ function generatedPositionAfter(mappingA, mappingB) {
+ // Optimized for most common case
+ var lineA = mappingA.generatedLine;
+ var lineB = mappingB.generatedLine;
+ var columnA = mappingA.generatedColumn;
+ var columnB = mappingB.generatedColumn;
+ return lineB > lineA || lineB == lineA && columnB >= columnA ||
+ util.compareByGeneratedPositions(mappingA, mappingB) <= 0;
+ }
+
+ /**
+ * A data structure to provide a sorted view of accumulated mappings in a
+ * performance conscious manner. It trades a neglibable overhead in general
+ * case for a large speedup in case of mappings being added in order.
+ */
+ function MappingList() {
+ this._array = [];
+ this._sorted = true;
+ // Serves as infimum
+ this._last = {generatedLine: -1, generatedColumn: 0};
+ }
+
+ /**
+ * Iterate through internal items. NOTE: order is NOT guaranteed.
+ */
+ MappingList.prototype.unsortedForEach = function MappingList_forEach() {
+ Array.prototype.forEach.apply(this._array, arguments);
+ };
+
+ /**
+ * Add the given source mapping.
+ *
+ * @param Object aMapping
+ */
+ MappingList.prototype.add = function MappingList_add(aMapping) {
+ var mapping;
+ if (generatedPositionAfter(this._last, aMapping)) {
+ this._last = aMapping;
+ this._array.push(aMapping);
+ } else {
+ this._sorted = false;
+ this._array.push(aMapping);
+ }
+ };
+
+ /**
+ * Returns the flat array representation of this structure.
+ * 
+ * WARNING: Returns internal data without copying, for performance
+ */
+ MappingList.prototype.toArray = function MappingList_toArray() {
+ if (this._sorted) {
+ return this._array;
+ } else {
+ // Sort runs in place
+ this._sorted = true;
+ return this._array.sort(util.compareByGeneratedPositions);
+ }
+ };
+
+ exports.MappingList = MappingList;
+
+});

lib/source-map/source-map-consumer.js

@@ -102,9 +102,9 @@ define(function (require, exports, module) {
  smc.sourceRoot);
  smc.file = aSourceMap._file;
 
- smc.__generatedMappings = aSourceMap._mappings.slice()
+ smc.__generatedMappings = aSourceMap._mappings.toArray()
  .sort(util.compareByGeneratedPositions);
- smc.__originalMappings = aSourceMap._mappings.slice()
+ smc.__originalMappings = aSourceMap._mappings.toArray()
  .sort(util.compareByOriginalPositions);
 
  return smc;

lib/source-map/source-map-generator.js

@@ -12,6 +12,7 @@ define(function (require, exports, module) {
  var base64VLQ = require('./base64-vlq');
  var util = require('./util');
  var ArraySet = require('./array-set').ArraySet;
+ var MappingList = require('./mapping-list').MappingList;
 
  /**
  * An instance of the SourceMapGenerator represents a source map which is
@@ -29,7 +30,7 @@ define(function (require, exports, module) {
  this._sourceRoot = util.getArg(aArgs, 'sourceRoot', null);
  this._sources = new ArraySet();
  this._names = new ArraySet();
- this._mappings = [];
+ this._mappings = new MappingList();
  this._sourcesContents = null;
  }
 
@@ -109,7 +110,7 @@ define(function (require, exports, module) {
  this._names.add(name);
  }
 
- this._mappings.push({
+ this._mappings.add({
  generatedLine: generated.line,
  generatedColumn: generated.column,
  originalLine: original != null && original.line,
@@ -186,7 +187,7 @@ define(function (require, exports, module) {
  var newNames = new ArraySet();
 
  // Find mappings for the "sourceFile"
- this._mappings.forEach(function (mapping) {
+ this._mappings.unsortedForEach(function (mapping) {
  if (mapping.source === sourceFile && mapping.originalLine != null) {
  // Check if it can be mapped by the source map, then update the mapping.
  var original = aSourceMapConsumer.originalPositionFor({
@@ -292,15 +293,10 @@ define(function (require, exports, module) {
  var result = '';
  var mapping;
 
- // The mappings must be guaranteed to be in sorted order before we start
- // serializing them or else the generated line numbers (which are defined
- // via the ';' separators) will be all messed up. Note: it might be more
- // performant to maintain the sorting as we insert them, rather than as we
- // serialize them, but the big O is the same either way.
- this._mappings.sort(util.compareByGeneratedPositions);
+ var mappings = this._mappings.toArray();
 
- for (var i = 0, len = this._mappings.length; i < len; i++) {
- mapping = this._mappings[i];
+ for (var i = 0, len = mappings.length; i < len; i++) {
+ mapping = mappings[i];
 
  if (mapping.generatedLine !== previousGeneratedLine) {
  previousGeneratedColumn = 0;
@@ -311,7 +307,7 @@ define(function (require, exports, module) {
  }
  else {
  if (i > 0) {
- if (!util.compareByGeneratedPositions(mapping, this._mappings[i - 1])) {
+ if (!util.compareByGeneratedPositions(mapping, mappings[i - 1])) {
  continue;
  }
  result += ',';