Implement ToLength from ES6 section 7.1.15

src/runtime.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This files contains runtime support implemented in JavaScript.
 
 // CAUTION: Some of the functions specified in this file are called
 // directly from compiled code. These are the functions with names in
 // ALL CAPS. The compiled code passes the first argument in 'this' and
 // it does not push the function onto the stack. This means that you
@@ skipping 573 matching lines @@
     if (NUMBER_IS_NAN(x) && NUMBER_IS_NAN(y)) return true;
     // x is +0 and y is -0 or vice versa.
     if (x === 0 && y === 0 && %_IsMinusZero(x) != %_IsMinusZero(y)) {
       return false;
     }
   }
   return x === y;
 }
 
 
+// ES6, draft 08-24-14, section 7.1.15

[rossberg, 2014/09/10 07:29:51]

Nit: move this next to ToInteger

[caitp (gmail), 2014/09/10 11:49:40]

Acknowledged.

+function ToLength(arg) {
+  arg = ToInteger(arg);
+  if (arg < +0) return 0;

[rossberg, 2014/09/10 07:29:51]

Nit: remove the +

[caitp (gmail), 2014/09/10 11:49:40]

Acknowledged.

+  return arg < $Number.MAX_SAFE_INTEGER ? arg : $Number.MAX_SAFE_INTEGER;
+}
+
+
 /* ---------------------------------
    - - -   U t i l i t i e s   - - -
    ---------------------------------
 */
 
 // Returns if the given x is a primitive value - not an object or a
 // function.
 function IsPrimitive(x) {
   // Even though the type of null is "object", null is still
   // considered a primitive value. IS_SPEC_OBJECT handles this correctly
@@ skipping 44 matching lines @@
   return i;
 }
 
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));