82 lines
2.8 KiB
C++
82 lines
2.8 KiB
C++
// Copyright 2022 Google LLC
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google LLC nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// safe_math.h: Helpful math functions.
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#ifndef SAFE_MATH_H__
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#define SAFE_MATH_H__
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#include <utility>
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namespace google_breakpad {
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// Adds `a` and `b`, returning a pair of:
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// - The result after any truncation.
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// - Whether an overflow/underflow occurred.
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template <typename T>
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std::pair<T, bool> AddWithOverflowCheck(T a, T b) {
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#ifdef _WIN32
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// Since C++11, unsigned overflow is well-defined; do everything unsigned,
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// assuming 2's complement.
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if (std::is_unsigned<T>::value) {
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T result = a + b;
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// Since we're adding two values >= 0, having a smaller value implies
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// overflow.
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bool overflow = result < a;
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return {result, overflow};
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}
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using TUnsigned = typename std::make_unsigned<T>::type;
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T result = TUnsigned(a) + TUnsigned(b);
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bool overflow;
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if ((a >= 0) == (b >= 0)) {
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if (a >= 0) {
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overflow = result < a;
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} else {
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overflow = result > a;
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}
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} else {
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// If signs are different, it's impossible for overflow to happen.
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overflow = false;
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}
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return {result, overflow};
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#else
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T result;
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bool overflow = __builtin_add_overflow(a, b, &result);
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return {result, overflow};
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#endif
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}
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template <typename T>
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T AddIgnoringOverflow(T a, T b) {
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return AddWithOverflowCheck(a, b).first;
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}
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} // namespace google_breakpad
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#endif // SAFE_MATH_H__
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