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Programming-Idioms

  • Python
  • Java

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.

import static java.lang.Math.addExact;
import static java.lang.Math.subtractExact;
boolean willOverflow(int x, int y) {
    try {
        addExact(x, y);
        subtractExact(x, y);
        return false;
    } catch (ArithmeticException e) {
        return true;
    }
}
public boolean addingWillOverflow(int x, int y){
    boolean willOverFlow = false;
    if(x > 0 && y > 0){
        if(y > (Integer.MAX_VALUE - x)){
            willOverFlow = true;
        }
    }
    if(x < 0 && y < 0){
       if(y < (Integer.MIN_VALUE - x)){
           willOverFlow = true;
       }
    }
    return willOverFlow;
}

If both values are positive, make sure the difference between one and the MAX_VALUE is less than the other, otherwise they will overflow.
If both values are negative, make sure the difference between one and the MIN_VALUE is less than the other, otherwise they will underflow.
The case where one is negative and one is positive does not need to be checked as they will definitely not under or overflow in that scenario.
def adding_will_overflow(x,y):
    return False

Python has arbitrary precision integers so you shouldn't worry about overflow.
Also, don't bother coding this constant function!
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...
< > ⌨
deleplace 
boolean willOverflow(int x, int y) {
    try {
        addExact(x, y);
        subtractExact(x, y);
        return false;
    } catch (ArithmeticException e) {
        return true;
    }
}
public boolean addingWillOverflow(int x, int y){
    boolean willOverFlow = false;
    if(x > 0 && y > 0){
        if(y > (Integer.MAX_VALUE - x)){
            willOverFlow = true;
        }
    }
    if(x < 0 && y < 0){
       if(y < (Integer.MIN_VALUE - x)){
           willOverFlow = true;
       }
    }
    return willOverFlow;
}
def adding_will_overflow(x,y):
    return False
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;
bool addingWillOverflow(int x, int y) {
  return ((x > 0) && (y > INT_MAX - x)) ||
         ((x < 0) && (y < INT_MIN - x));
}
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));
}
bool addingWillOverflow(int x, int y)
{
  bool willOverflow = false;

  if (x > 0 && y > 0)
    if (y > (int.MaxValue - x)) willOverflow = true;

  if (x < 0 && y < 0)
    if (y < (int.MinValue - x)) willOverflow = true;

  return willOverflow;
}
bool addingWillOverflow(int x, int y)
{
    bool result;
    core.checkedint.adds(x, y, result);
    return result;
}
  logical function adding_will_overflow (x,y) result(res)
    integer, intent(in) :: x, y
    res = (x > 0 .and. y > huge(x) - x) .or. (x < 0 .and. y < huge(x) - x)
  end function adding_will_overflow
func addingWillOverflow(x int, y int) bool {
	if x > 0 {
		return y > math.MaxInt-x
	}
	return y < math.MinInt-x
}
addingWillOverflow x y = y > maxBound - x
function addingWillOverflow(x, y) {
  return x > 0 && y > 0 && x > Number.MAX_SAFE_INTEGER - y
}

local function intadding_will_overflow(x,y)
 return x>0
  and y>0 and x+y<x
  or y<0 and x+y>x
end
function _addingWillOverflow($x, $y): bool
{
    return (PHP_INT_MAX - $y) > $x;
}
function AddingWillOverFlow(x,y: Integer): Boolean;
begin
  Result := ((x > 0) and (y > 0) and (x > (High(Integer)-y))) or
            ((x < 0) and (y < 0) and ((Low(Integer)-x) > y));
end;
function AddingWillOverFlow(x,y: Integer): Boolean;
begin
  Result := (x > 0) and (y > 0) and (x > (MaxInt-y));
end;
sub adding_will_overflow {
    my ($x, $y) = @_;
    return 'Inf' eq $x + $y;
}

def addingWillOverflow(x,y)
  false
end
fn adding_will_overflow(x: usize, y: usize) -> bool {
    x.checked_add(y).is_none()
}