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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

'require util/polyfill';

$jscomp.polyfill('Math.imul', function(orig) {
  if (orig) return orig;

  /**
   * Performs C-like 32-bit signed integer multiplication.
   *
   * Polyfills the static function Math.imul().
   *
   * @param {number} a Any number, or value that can be coerced to a number.
   * @param {number} b Any number, or value that can be coerced to a number.
   * @return {number} The 32-bit integer product of a and b.
   */
  var polyfill = function(a, b) {
    // This algorithm is taken from v8.
    // Note: If multiplication overflows 32 bits, then we risk losing
    // precision.  We must therefore break the inputs into 16-bit
    // words and multiply separately.
    a = Number(a);
    b = Number(b);
    var ah = (a >>> 16) & 0xFFFF;  // Treat individual words as unsigned
    var al = a & 0xFFFF;
    var bh = (b >>> 16) & 0xFFFF;
    var bl = b & 0xFFFF;
    var lh = ((ah * bl + al * bh) << 16) >>> 0;  // >>> 0 casts to uint
    return (al * bl + lh) | 0;  // | 0 casts back to signed
  };

  return polyfill;
}, 'es6', 'es3');