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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';
'require util/defines';

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

  if ($jscomp.SIMPLE_FROUND_POLYFILL || typeof Float32Array !== 'function') {
    // Explicitly requested a no-op polyfill, or Float32Array not available.
    return /** @return {number} */ function(/** number */ arg) {
      return arg;
    };
  }

  var arr = new Float32Array(1);
  /**
   * Rounds the given double-precision number to single-precision (float32).
   *
   * Polyfills the static function Math.fround().
   *
   * This polyfill is slightly incorrect for IE8 and IE9, where it performs no
   * rounding at all. This is generally not a problem, since Math.fround is
   * primarily used for optimization (to force faster 32-bit operations rather
   * than 64-bit), but in cases where (a) the logic actually depends on a
   * correct fround implementation and (b) the application targets very old
   * browsers, this polyfill will be insufficient.  For that case, see
   * https://gist.github.com/shicks/7a97ec6b3f10212e60a89a7f6d2d097d for a
   * more correct polyfill that does not depend on Float32Array.
   *
   * @param {number} arg A 64-bit double-precision number.
   * @return {number} The closest float32 to the argument.
   */
  var polyfill = function(arg) {
    arr[0] = arg;
    return arr[0];
  };
  return polyfill;
}, 'es6', 'es3');