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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 
     14 // -------------------------------------------------------------------
     15 // http://tc39.github.io/proposal-string-pad-start-end/
     16 
     17 function StringPad(thisString, maxLength, fillString) {
     18   maxLength = TO_LENGTH(maxLength);
     19   var stringLength = thisString.length;
     20 
     21   if (maxLength <= stringLength) return "";
     22 
     23   if (IS_UNDEFINED(fillString)) {
     24     fillString = " ";
     25   } else {
     26     fillString = TO_STRING(fillString);
     27     if (fillString === "") {
     28       // If filler is the empty String, return S.
     29       return "";
     30     }
     31   }
     32 
     33   var fillLength = maxLength - stringLength;
     34   var repetitions = (fillLength / fillString.length) | 0;
     35   var remainingChars = (fillLength - fillString.length * repetitions) | 0;
     36 
     37   var filler = "";
     38   while (true) {
     39     if (repetitions & 1) filler += fillString;
     40     repetitions >>= 1;
     41     if (repetitions === 0) break;
     42     fillString += fillString;
     43   }
     44 
     45   if (remainingChars) {
     46     filler += %_SubString(fillString, 0, remainingChars);
     47   }
     48 
     49   return filler;
     50 }
     51 
     52 function StringPadStart(maxLength, fillString) {
     53   CHECK_OBJECT_COERCIBLE(this, "String.prototype.padStart")
     54   var thisString = TO_STRING(this);
     55 
     56   return StringPad(thisString, maxLength, fillString) + thisString;
     57 }
     58 %FunctionSetLength(StringPadStart, 1);
     59 
     60 function StringPadEnd(maxLength, fillString) {
     61   CHECK_OBJECT_COERCIBLE(this, "String.prototype.padEnd")
     62   var thisString = TO_STRING(this);
     63 
     64   return thisString + StringPad(thisString, maxLength, fillString);
     65 }
     66 %FunctionSetLength(StringPadEnd, 1);
     67 
     68 utils.InstallFunctions(GlobalString.prototype, DONT_ENUM, [
     69   "padStart", StringPadStart,
     70   "padEnd", StringPadEnd
     71 ]);
     72 
     73 });
     74