Question

How do I eliminate the ternary operator from the code below? I’m looking for something using only integer operators (shifts, additions, etc).

a = (a < 0) ? (-a * 2) - 1 : (a * 2)

Answer 1

Off the top of my head, assuming a is an int:

a = 2*a*(1+2*(a>>31)) - (a>>>31);

>> is arithmetic (signed) shift left. So a>>31 replaces all the bits with the sign bit. All bits set gives -1. Multiple by two and add one, negatives go to -1 and positives (and zero) to 1.

>>> is logical (unsigned) shift left. So a>>>31 clears the top 31 bits and places the sign bit in bit 0 (0 for positive numbers and zero; 1 for negative numbers).

The “proper” way of doing something vaguely like this is:

a ^= a>>31;
a *= 2;