CODEWITHSUNDEEP
javamathinteger-overflow
user7466895
user7466895

Reputation: 319

Java finding the midpoint between two integers

I'm attempting to find the integer midpoint between two integers. For example mid(2,3) would be 2, not 2.5. I had the below which works fine, but i'd like to work with numbers from MIN_VALUE to MAX_VALUE, and doing so causes overflow so completely incorrect results.

public static int mid(int x, int y){
    int midpoint =  (x+y)/2;
    return midpoint;
}

I've now got:

public static int mid(int x, int y){
    int low = Math.min(x, y);
    int high = Math.max(x, y);
    int midpoint =  (low + high) >>> 1;
    return midpoint;
}

This seems to work for values of x and y from 0 up to Integer.MAX_VALUE, however is incorrect if x is a negative number and i'm unsure why that is?

Upvotes: 2

Views: 10247

Answers (4)

Linh Nguyen
Linh Nguyen

Reputation: 1138

How about this one?

public static int mid(int x, int y) {
   return x/2 + y/2 + (x%2 + y%2)/2;
}

Upvotes: 4

bin he
bin he

Reputation: 187

a >>> operator fills the top bits with zero, unlike >> which extends the sign bit into the top bits.so bitwise operator >> is helpful:

public static int mid(int x, int y){
   int midpoint =  (x>>1) + (y>>1);

    if((x&0b1)/0b1==1&&(y&0b1)/0b1==1){
        midpoint++;
    }

    return midpoint;
}

for example: 1111 1110(decimal -2) + 0000 0001(decimal 1) = 1111 1111(decimal -1)

1111 1111(decimal -1)>>1 = 1111 1111(decimal -1)

while

1111 1111(decimal -1)>>>1 = 0111 1111(decimal 127)

(java type 'Integer' is 4 bytes,here just to illustrate )

I think this may be useful to understand the result;

Upvotes: 1

Michael Sharp
Michael Sharp

Reputation: 496

What about something like this?

public static int mid(int x, int y){
    long difference = (long)y - x;
    long adDiff = difference/2;
    return (long) (x + adDiff);
}

You have to cast it to a long so that in the instance where y-x is greater then MAX_VALUE you don't overflow.

Upvotes: 1

Viet
Viet

Reputation: 3409

You can work around with convert to long and back:

public static int mid(int x, int y) {
    return (int) (((long)x + y) / 2);
}

Upvotes: 2

Related Questions