Reputation: 104702

Reduce one from absolute value?

I have an integer that needs its absolute value to be reduced by one.

Is there a shorter way than this:

if(number > 0) number--; else if (number < 0) number++;

Upvotes: 2

Answers (4)

David Sherret

Reputation: 106630

Even shorter:

number -= Math.Sign(number);

Math.Sign returns -1, 0, or 1 depending on the sign of the specified value.

Extension Method

Since you say you face this situation a lot it might be beneficial to make this an extension method to better express your intent:

public static int ReduceFromAbsoluteValue(this int number, int reduceValue)
{
    return number - Math.Sign(number) * reduceValue;
}

4.ReduceFromAbsoluteValue(1);  // 3
-4.ReduceFromAbsoluteValue(1); // -3
0.ReduceFromAbsoluteValue(1);  // 0

Alternatively name this AddToAbsoluteValue and change it to add the value.

Upvotes: 5

user555045

Reputation: 64904

Hack time!

return number - (number >> 31) + (-number >> 31);

x >> 31 will be -1 if x < 0, 0 otherwise. So if number < 0 it will subtract -1 (add 1). If number > 0 then -number < 0 and it adds -1 if number > 0. Both things are zero when number == 0 so it leaves that alone.

Upvotes: 2