c++ - get absolute value without using abs function nor if statement

Question

I was thinking how to get the absolute value of an integer without using if statement nor abs(). At first I was using shift bits left (<<), trying to get negative sign out of the range, then shift bits right back to where it be, but unfortunately it doesn't work for me. Please let me know why it isn't working and other alternatives ways to do it.

Answer 1

From Bit Twiddling Hacks:

int v;           // we want to find the absolute value of v
unsigned int r;  // the result goes here 
int const mask = v >> sizeof(int) * CHAR_BIT - 1;

r = (v + mask) ^ mask;