Question

I know that I can perform divide by 2 using right shift.

For simplicity, take a 4 bit number system

-1 - 1111
-2 - 1110
-3 - 1101
-4 - 1100
-5 - 1011
-6 - 1010
-7 - 1001
-8 - 1000
7  - 0111
6  - 0110
5  - 0101
4  - 0100
3  - 0011
2  - 0010
1  - 0001
0  - 0000

If I try to perform

6 / 2 = 0110 >> 1 = 0011 = 3
-6/ 2 = 1010 >> 1 = 1101 = -3

Is valid for both +ve and -ve number

However, when come to 1

1 / 2 = 0001 >> 1 = 0000 = 0
-1/ 2 = 1111 >> 1 = 1111 = -1

Seems like there is a special case in -1, as right shift then to move it to negative infinity.

Currently, I need to put a special if check for this, as I am expecting -1 / 2 = 0.

I was wondering how do you guy handle this exception in your code? You guy put an if check?

Answer 1

Any negative odd number won’t work. However to answer your question, if you know you can have negative numbers, just divide by 2. This is turned into a shift with a fixup by the jit/compiler.