1 /*
2 * Copyright 2014 Google Inc. All rights reserved.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "checked_adder.h"
18
19 #include <climits>
20 #include <iostream>
21
22 class CheckedAdder : public Adder {
23 private:
add_overflows(int x,int y)24 bool add_overflows(int x, int y) {
25 if (y > x)
26 std::swap(x, y);
27 // Now y <= x.
28 const int half_max = INT_MAX / 2;
29 const int half_min = INT_MIN / 2;
30 if (x > half_max) {
31 // We can't have negative overflow, but might have positive overflow.
32 if (y > half_max)
33 return true;
34 if (y <= 0)
35 return false;
36 // x <= INT_MAX && y <= half_max,
37 // so: x + y <= INT_MAX + half_max
38 // so: x - half_max + y <= INT_MAX
39 // so: (x - half_max + y) doesn't overflow.
40 // (x + y) > INT_MAX iff (x - half_max + y) > (INT_MAX - half_max)
41 return (x - half_max + y) > (INT_MAX - half_max);
42 }
43 // y <= x <= half_max, can't have positive overflow.
44 if (y < half_min) {
45 // We can't have positive overflow, but might have negative overflow.
46 if (x < half_min)
47 return true;
48 if (x >= 0)
49 return false;
50 // y >= INT_MIN && x >= half_min,
51 // so: y + x >= INT_MIN + half_min
52 // so: y - half_min + x >= INT_MAX
53 // so: (y - half_min + x) doesn't overflow.
54 // (y + x) < INT_MIN iff (y - half_min + x) < (INT_MIN - half_min)
55 return (y - half_min + x) < (INT_MIN - half_min);
56 }
57 // Neither negative nor positive overflow.
58 return false;
59 }
60
61 public:
62 INJECT(CheckedAdder()) = default;
63
add(int x,int y)64 virtual int add(int x, int y) override {
65 if (add_overflows(x, y)) {
66 std::cerr << "CheckedAdder: detected overflow during addition of " << x << " and " << y << std::endl;
67 abort();
68 }
69 return x + y;
70 }
71 };
72
getCheckedAdderComponent()73 fruit::Component<Adder> getCheckedAdderComponent() {
74 return fruit::createComponent().bind<Adder, CheckedAdder>();
75 }
76