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Programming-Idioms

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  • Haskell

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.

addingWillOverflow x y = y > maxBound - x

Integers in Haskell are arbitrary sized. But Int:s etc aren't.

This would function would work for any Numeric types with a maxbound (such as Int, Word8 etc).

PROBLEM: this doesn't detect negative overflow.
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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