| 1 | // Copyright (c) 2018 Robert Ramey |
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| 2 | // |
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| 3 | // Distributed under the Boost Software License, Version 1.0. (See |
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| 4 | // accompanying file LICENSE_1_0.txt or copy at |
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| 5 | // http://www.boost.org/LICENSE_1_0.txt) |
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| 6 | |
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| 7 | #include <iostream> |
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| 8 | |
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| 9 | #include <boost/safe_numerics/safe_integer.hpp> |
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| 10 | |
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| 11 | int main(int, const char *[]){ |
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| 12 | std::cout << "example 3:" ; |
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| 13 | std::cout << "undetected underflow in data type" << std::endl; |
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| 14 | std::cout << "Not using safe numerics" << std::endl; |
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| 15 | // problem: decrement can yield incorrect result |
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| 16 | try{ |
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| 17 | unsigned int x = 0; |
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| 18 | // the following silently produces an incorrect result |
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| 19 | --x; |
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| 20 | std::cout << x << " != " << -1 << std::endl; |
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| 21 | |
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| 22 | // when comparing int and unsigned int, C++ converts |
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| 23 | // the int to unsigned int so the following assertion |
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| 24 | // fails to detect the above error! |
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| 25 | assert(x == -1); |
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| 26 | |
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| 27 | std::cout << "error NOT detected!" << std::endl; |
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| 28 | } |
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| 29 | catch(const std::exception &){ |
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| 30 | // never arrive here |
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| 31 | std::cout << "error detected!" << std::endl; |
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| 32 | } |
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| 33 | // solution: replace unsigned int with safe<unsigned int> |
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| 34 | std::cout << "Using safe numerics" << std::endl; |
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| 35 | try{ |
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| 36 | using namespace boost::safe_numerics; |
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| 37 | safe<unsigned int> x = 0; |
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| 38 | // decrement unsigned to less than zero throws exception |
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| 39 | --x; |
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| 40 | assert(false); // never arrive here |
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| 41 | } |
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| 42 | catch(const std::exception & e){ |
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| 43 | std::cout << e.what() << std::endl; |
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| 44 | std::cout << "error detected!" << std::endl; |
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| 45 | } |
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| 46 | return 0; |
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| 47 | } |
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| 48 | |
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