No IntegerDivisionByZeroException in Leg (as it only has doubles). Also fix a rounding issue.

dart/frog/leg/lib/js_helper.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('js_helper');
 
 #import('coreimpl.dart');
 
 #source('date_helper.dart');
 #source('regexp_helper.dart');
 #source('string_helper.dart');
 
 /**
-  * Returns true if both arguments are numbers.
-  * If only the first argument is a number, throws the given message as
-  * exception.
-  */
-bool checkNumbers(var a, var b, var message) {
+ * Returns true if both arguments are numbers.
+ *
+ * If only the first argument is a number, an
+ * [IllegalArgumentException] with the other argument is thrown.
+ */
+bool checkNumbers(var a, var b) {
   if (a is num) {
     if (b is num) {
       return true;
     } else {
       checkNull(b);
-      throw new IllegalArgumentException(message);
+      throw new IllegalArgumentException(b);
     }
   }
   return false;
 }
 
 
 bool isJsArray(var value) {
   return value !== null && JS('bool', @'$0.constructor === Array', value);
 }
 
 
 add(var a, var b) {
-  if (checkNumbers(a, b, 'num+ expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 + $1', a, b);
   } else if (a is String) {
     b = b.toString();
     if (b is String) {
       return JS('String', @'$0 + $1', a, b);
     }
     checkNull(b);
     throw new IllegalArgumentException(b);
   }
   checkNull(a);
   return UNINTERCEPTED(a + b);
 }
 
 div(var a, var b) {
-  if (checkNumbers(a, b, 'num/ expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 / $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a / b);
 }
 
 mul(var a, var b) {
-  if (checkNumbers(a, b, 'num* expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 * $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a * b);
 }
 
 sub(var a, var b) {
-  if (checkNumbers(a, b, 'num- expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 - $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a - b);
 }
 
 mod(var a, var b) {
-  if (checkNumbers(a, b, 'int% expects an int as second operand.')) {
-    if (b === 0) throw new IntegerDivisionByZeroException();
+  if (checkNumbers(a, b)) {
     // Euclidean Modulo.
     int result = JS('num', @'$0 % $1', a, b);
     if (result == 0) return 0;  // Make sure we don't return -0.0.
     if (result > 0) return result;
     if (b < 0) {
       return result - b;
     } else {
       return result + b;
     }
   }
   checkNull(a);
   return UNINTERCEPTED(a % b);
 }
 
 tdiv(var a, var b) {
-  if (checkNumbers(a, b, 'num~/ expects a number as second operand.')) {
-    if (b === 0) throw new IntegerDivisionByZeroException();
+  if (checkNumbers(a, b)) {
     return (a / b).truncate();
   }
   checkNull(a);
   return UNINTERCEPTED(a ~/ b);
 }
 
 eq(var a, var b) {
   if (JS('bool', @'typeof $0 === "object"', a)) {
     if (JS_HAS_EQUALS(a)) {
       return UNINTERCEPTED(a == b) === true;
@@ skipping 15 matching lines @@
       return UNINTERCEPTED(a == null) === true;
     } else {
       return false;
     }
   } else {
     return JS('bool', @'typeof $0 === "undefined"', a);
   }
 }
 
 gt(var a, var b) {
-  if (checkNumbers(a, b, 'num> expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('bool', @'$0 > $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a > b);
 }
 
 ge(var a, var b) {
-  if (checkNumbers(a, b, 'num>= expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('bool', @'$0 >= $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a >= b);
 }
 
 lt(var a, var b) {
-  if (checkNumbers(a, b, 'num< expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('bool', @'$0 < $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a < b);
 }
 
 le(var a, var b) {
-  if (checkNumbers(a, b, 'num<= expects a number as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('bool', @'$0 <= $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a <= b);
 }
 
 shl(var a, var b) {
   // TODO(floitsch): inputs must be integers.
-  if (checkNumbers(a, b, 'int<< expects an int as second operand.')) {
+  if (checkNumbers(a, b)) {
     if (b < 0) throw new IllegalArgumentException(b);
     return JS('num', @'$0 << $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a << b);
 }
 
 shr(var a, var b) {
   // TODO(floitsch): inputs must be integers.
-  if (checkNumbers(a, b, 'int>> expects an int as second operand.')) {
+  if (checkNumbers(a, b)) {
     if (b < 0) throw new IllegalArgumentException(b);
     return JS('num', @'$0 >> $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a >> b);
 }
 
 and(var a, var b) {
   // TODO(floitsch): inputs must be integers.
-  if (checkNumbers(a, b, 'int& expects an int as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 & $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a & b);
 }
 
 or(var a, var b) {
   // TODO(floitsch): inputs must be integers.
-  if (checkNumbers(a, b, 'int| expects an int as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 | $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a | b);
 }
 
 xor(var a, var b) {
   // TODO(floitsch): inputs must be integers.
-  if (checkNumbers(a, b, 'int^ expects an int as second operand.')) {
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 ^ $1', a, b);
   }
   checkNull(a);
   return UNINTERCEPTED(a ^ b);
 }
 
 not(var a) {
   if (JS('bool', @'typeof $0 === "number"', a)) return JS('num', @'~$0', a);
   checkNull(a);
   return UNINTERCEPTED(~a);
@@ skipping 305 matching lines @@
     checkNull(str);
     if (str is !String) throw new IllegalArgumentException(str);
     var value = JS('num', @'Date.parse($0)', str);
     if (value.isNaN()) throw new IllegalArgumentException(str);
     return value;
   }
 }
 
 builtin$compareTo$1(a, b) {
   checkNull(a);
-  if (checkNumbers(a, b, 'illegal argument')) {
+  if (checkNumbers(a, b)) {
     if (a < b) {
       return -1;
     } else if (a > b) {
       return 1;
     } else if (a == b) {
       if (a == 0) {
         bool aIsNegative = a.isNegative();
         bool bIsNegative = b.isNegative();
         if (aIsNegative == bIsNegative) return 0;
         if (aIsNegative) return -1;
@@ skipping 324 matching lines @@
   checkNull(receiver);
   if (receiver is num) {
     return JS('bool', @'isNaN($0)', receiver);
   } else {
     return UNINTERCEPTED(receiver.isNegative());
   }
 }
 
 builtin$remainder$1(a, b) {
   checkNull(a);
-  if (checkNumbers(a, b, 'num.remainder expects a number as second operand.')) {
-    if (b === 0) throw new IntegerDivisionByZeroException();
+  if (checkNumbers(a, b)) {
     return JS('num', @'$0 % $1', a, b);
   } else {
     return UNINTERCEPTED(a.remainder(b));
   }
 }
 
 builtin$abs$0(receiver) {
   checkNull(receiver);
   if (receiver is !num) return UNINTERCEPTED(receiver.abs());
 
@@ skipping 38 matching lines @@
   checkNull(receiver);
   if (receiver is !num) return UNINTERCEPTED(receiver.negate());
 
   return JS('num', @'-$0', receiver);
 }
 
 builtin$round$0(receiver) {
   checkNull(receiver);
   if (receiver is !num) return UNINTERCEPTED(receiver.round());
 
-  return JS('num', @'Math.round($0)', receiver);
+  if (JS('bool', @'$0 < 0', receiver)) {
+    return JS('num', @'-Math.round(-$0)', receiver);
+  } else {
+    return JS('num', @'Math.round($0)', receiver);
+  }
 }
 
 builtin$toDouble$0(receiver) {
   checkNull(receiver);
   if (receiver is !num) return UNINTERCEPTED(receiver.toDouble());
 
   // TODO(ahe): Just return receiver?
   return JS('double', @'$0 + 0', receiver);
 }
 
@@ skipping 344 matching lines @@
       }
     }
   } else if (JS('bool', @'$0 instanceof RangeError', ex)) {
     var message = JS('String', @'$0.message', ex);
     if (message.contains('call stack')) {
       return new StackOverflowException();
     }
   }
   return ex;
 }