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