fastest way to negate a number

Question

I was thinking this morning here, what would be the fastest way to reverse a number of positive to negative and from negative to positive, of course, the simplest way might

Answer 1

Solution using high level language

Questions like these are popular in interviews and competitive programming world .

I landed here researching more solution for negation of a number without using - or + operator .

For this :

1. complement a number using ~ operator
2. Then add 1 to the number obtained in step 1 using Half adder logic :

> int addNumbers(int x, int y)
>       {
>                    if(y==0)  return x; // carry is 0 
>                    return addNumbers(x^y,(x&y)<<1);
>         }

Here x^y performs addition of bits and x&y handles carry operation