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