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      1 // Copyright 2016 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 (function(global, utils) {
      6 
      7 %CheckIsBootstrapping();
      8 
      9 // -------------------------------------------------------------------
     10 // Imports
     11 
     12 var GlobalString = global.String;
     13 var MakeTypeError;
     14 
     15 utils.Import(function(from) {
     16   MakeTypeError = from.MakeTypeError;
     17 });
     18 
     19 // -------------------------------------------------------------------
     20 // http://tc39.github.io/proposal-string-pad-start-end/
     21 
     22 function StringPad(thisString, maxLength, fillString) {
     23   maxLength = TO_LENGTH(maxLength);
     24   var stringLength = thisString.length;
     25 
     26   if (maxLength <= stringLength) return "";
     27 
     28   if (IS_UNDEFINED(fillString)) {
     29     fillString = " ";
     30   } else {
     31     fillString = TO_STRING(fillString);
     32     if (fillString === "") {
     33       // If filler is the empty String, return S.
     34       return "";
     35     }
     36   }
     37 
     38   var fillLength = maxLength - stringLength;
     39   var repetitions = (fillLength / fillString.length) | 0;
     40   var remainingChars = (fillLength - fillString.length * repetitions) | 0;
     41 
     42   var filler = "";
     43   while (true) {
     44     if (repetitions & 1) filler += fillString;
     45     repetitions >>= 1;
     46     if (repetitions === 0) break;
     47     fillString += fillString;
     48   }
     49 
     50   if (remainingChars) {
     51     filler += %_SubString(fillString, 0, remainingChars);
     52   }
     53 
     54   return filler;
     55 }
     56 
     57 function StringPadStart(maxLength, fillString) {
     58   CHECK_OBJECT_COERCIBLE(this, "String.prototype.padStart")
     59   var thisString = TO_STRING(this);
     60 
     61   return StringPad(thisString, maxLength, fillString) + thisString;
     62 }
     63 %FunctionSetLength(StringPadStart, 1);
     64 
     65 function StringPadEnd(maxLength, fillString) {
     66   CHECK_OBJECT_COERCIBLE(this, "String.prototype.padEnd")
     67   var thisString = TO_STRING(this);
     68 
     69   return thisString + StringPad(thisString, maxLength, fillString);
     70 }
     71 %FunctionSetLength(StringPadEnd, 1);
     72 
     73 utils.InstallFunctions(GlobalString.prototype, DONT_ENUM, [
     74   "padStart", StringPadStart,
     75   "padEnd", StringPadEnd
     76 ]);
     77 
     78 });
     79