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Programming-Idioms

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  • C++

Idiom #85 Check if integer addition will overflow

Write boolean function addingWillOverflow which takes two integers x, y and return true if (x+y) overflows.

An overflow may be above the max positive value, or below the min negative value.

#include <limits>
bool addingWillOverflow(int x, int y) {
  return ((x > 0) && (y > std::numeric_limits<int>::max() - x)) ||
         ((x < 0) && (y < std::numeric_limits<int>::min() - x));
}
function Adding_Will_Overflow (X, Y : Integer) return Boolean is
begin
   return X > 0 and Y > 0 and X > Integer'Last - Y;
end Adding_Will_Overflow;

PROBLEM: this doesn't detect negative overflow.

New implementation...
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