Bug 874764 - Add CheckedInt support for operator%. - r=bjacob,waldo

mfbt/CheckedInt.h

@@ -450,6 +450,44 @@ IsDivValid(T x, T y)
          !(IsSigned<T>::value && x == MinValue<T>::value && y == T(-1));
 }
 
+template<typename T, bool IsTSigned = IsSigned<T>::value>
+struct IsModValidImpl;
+
+template<typename T>
+inline bool
+IsModValid(T x, T y)
+{
+  return IsModValidImpl<T>::run(x, y);
+}
+
+/*
+ * Mod is pretty simple.
+ * For now, let's just use the ANSI C definition:
+ * If x or y are negative, the results are implementation defined.
+ *   Consider these invalid.
+ * Undefined for y=0.
+ * The result will never exceed either x or y.
+ *
+ * Checking that x>=0 is a warning when T is unsigned.
+ */
+
+template<typename T>
+struct IsModValidImpl<T, false> {
+  static inline bool run(T x, T y) {
+    return y >= 1;
+  }
+};
+
+template<typename T>
+struct IsModValidImpl<T, true> {
+  static inline bool run(T x, T y) {
+    if (x < 0)
+      return false;
+
+    return y >= 1;
+  }
+};
+
 template<typename T, bool IsSigned = IsSigned<T>::value>
 struct NegateImpl;
 
@@ -619,22 +657,31 @@ class CheckedInt
                                     const CheckedInt<U>& rhs);
     template<typename U>
     CheckedInt& operator +=(U rhs);
+
     template<typename U>
     friend CheckedInt<U> operator -(const CheckedInt<U>& lhs,
                                     const CheckedInt<U>& rhs);
     template<typename U>
     CheckedInt& operator -=(U rhs);
+
     template<typename U>
     friend CheckedInt<U> operator *(const CheckedInt<U>& lhs,
                                     const CheckedInt<U>& rhs);
     template<typename U>
     CheckedInt& operator *=(U rhs);
+
     template<typename U>
     friend CheckedInt<U> operator /(const CheckedInt<U>& lhs,
                                     const CheckedInt<U>& rhs);
     template<typename U>
     CheckedInt& operator /=(U rhs);
 
+    template<typename U>
+    friend CheckedInt<U> operator %(const CheckedInt<U>& lhs,
+                                    const CheckedInt<U>& rhs);
+    template<typename U>
+    CheckedInt& operator %=(U rhs);
+
     CheckedInt operator -() const
     {
       return detail::NegateImpl<T>::negate(*this);
@@ -726,6 +773,7 @@ MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Add, +)
 MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Sub, -)
 MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Mul, *)
 MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Div, /)
+MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Mod, %)
 
 #undef MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR
 
@@ -786,6 +834,7 @@ MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(+, +=)
 MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(*, *=)
 MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(-, -=)
 MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(/, /=)
+MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(%, %=)
 
 #undef MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS
 

mfbt/tests/TestCheckedInt.cpp

@@ -190,6 +190,26 @@ void test()
     VERIFY_IS_INVALID(one - min + min);
   }
 
+  /* Modulo checks */
+  VERIFY_IS_INVALID(zero % zero);
+  VERIFY_IS_INVALID(one % zero);
+  VERIFY_IS_VALID(zero % one);
+  VERIFY_IS_VALID(zero % max);
+  VERIFY_IS_VALID(one % max);
+  VERIFY_IS_VALID(max % one);
+  VERIFY_IS_VALID(max % max);
+  if (isTSigned) {
+    const CheckedInt<T> minusOne = zero - one;
+    VERIFY_IS_INVALID(minusOne % minusOne);
+    VERIFY_IS_INVALID(zero % minusOne);
+    VERIFY_IS_INVALID(one % minusOne);
+    VERIFY_IS_INVALID(minusOne % one);
+
+    VERIFY_IS_INVALID(min % min);
+    VERIFY_IS_INVALID(zero % min);
+    VERIFY_IS_INVALID(min % one);
+  }
+
   /* Unary operator- checks */
 
   const CheckedInt<T> negOne = -one;
@@ -347,10 +367,15 @@ void test()
   VERIFY_IS_INVALID(someInvalid / one);
   VERIFY_IS_INVALID(zero / someInvalid);
   VERIFY_IS_INVALID(one / someInvalid);
+  VERIFY_IS_INVALID(someInvalid % zero);
+  VERIFY_IS_INVALID(someInvalid % one);
+  VERIFY_IS_INVALID(zero % someInvalid);
+  VERIFY_IS_INVALID(one % someInvalid);
   VERIFY_IS_INVALID(someInvalid + someInvalid);
   VERIFY_IS_INVALID(someInvalid - someInvalid);
   VERIFY_IS_INVALID(someInvalid * someInvalid);
   VERIFY_IS_INVALID(someInvalid / someInvalid);
+  VERIFY_IS_INVALID(someInvalid % someInvalid);
 
   /* Check that mixing checked integers with plain integers in expressions is allowed */
 
@@ -382,6 +407,13 @@ void test()
     x /= 2;
     VERIFY(x == two);
   }
+  VERIFY(three % 2 == one);
+  VERIFY(3 % two == one);
+  {
+    CheckedInt<T> x = three;
+    x %= 2;
+    VERIFY(x == one);
+  }
 
   VERIFY(one == 1);
   VERIFY(1 == one);