Change sign using bitwise operators

Question

How to change the sign of int using bitwise operators? Obviously we can use x*=-1 or x/=-1. Is there any fastest way of doing this?

I did a sm

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

Answer 2

The speed difference between non-floating point (e.g. int math) addition/multiplication and bitwise operations is less than negligible on almost all machines.

There is no general way to turn an n-bit signed integer into its negative equivalent using only bitwise operations, as the negation operation looks like x = (~x) + 1, which requires one addition. However, assuming the signed integer is 32 bit you can probably write a bitwise equation to do this calculation. Note: do not do this.

The most common, readable way to negate a number is x = -x.

Answer 3

Java uses Complement Two representation. In order to change a sign, it means you must do a bitwise negation (it would be equivalent to xor with FFFF) and add 1.

x = ~x + 1;

I am almost sure that -x is, if anything, faster than that.