| /* |
| * Copyright 2014 Google Inc. All rights reserved. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include "checked_adder.h" |
| |
| #include <climits> |
| #include <iostream> |
| |
| class CheckedAdder : public Adder { |
| private: |
| bool add_overflows(int x, int y) { |
| if (y > x) |
| std::swap(x, y); |
| // Now y <= x. |
| const int half_max = INT_MAX / 2; |
| const int half_min = INT_MIN / 2; |
| if (x > half_max) { |
| // We can't have negative overflow, but might have positive overflow. |
| if (y > half_max) |
| return true; |
| if (y <= 0) |
| return false; |
| // x <= INT_MAX && y <= half_max, |
| // so: x + y <= INT_MAX + half_max |
| // so: x - half_max + y <= INT_MAX |
| // so: (x - half_max + y) doesn't overflow. |
| // (x + y) > INT_MAX iff (x - half_max + y) > (INT_MAX - half_max) |
| return (x - half_max + y) > (INT_MAX - half_max); |
| } |
| // y <= x <= half_max, can't have positive overflow. |
| if (y < half_min) { |
| // We can't have positive overflow, but might have negative overflow. |
| if (x < half_min) |
| return true; |
| if (x >= 0) |
| return false; |
| // y >= INT_MIN && x >= half_min, |
| // so: y + x >= INT_MIN + half_min |
| // so: y - half_min + x >= INT_MAX |
| // so: (y - half_min + x) doesn't overflow. |
| // (y + x) < INT_MIN iff (y - half_min + x) < (INT_MIN - half_min) |
| return (y - half_min + x) < (INT_MIN - half_min); |
| } |
| // Neither negative nor positive overflow. |
| return false; |
| } |
| |
| public: |
| INJECT(CheckedAdder()) = default; |
| |
| virtual int add(int x, int y) override { |
| if (add_overflows(x, y)) { |
| std::cerr << "CheckedAdder: detected overflow during addition of " << x << " and " << y << std::endl; |
| abort(); |
| } |
| return x + y; |
| } |
| }; |
| |
| fruit::Component<Adder> getCheckedAdderComponent() { |
| return fruit::createComponent().bind<Adder, CheckedAdder>(); |
| } |