Does the Java compiler or the JIT compiler optimize divisions or multiplications by a constant power of two down to bitshifting?
For example, are the following two statements optimized to be the same?
int median = start + (end - start) >>> 1;
int median = start + (end - start) / 2;
(basically this question but for Java)
No, the Java compiler doesn't do that, because it can't be sure on what the sign of (end - start) will be. Why does this matter? Bit shifts on negative integers yield a different result than an ordinary division. Here you can see a demo: this simple test:
System.out.println((-10) >> 1); // prints -5
System.out.println((-11) >> 1); // prints -6
System.out.println((-11) / 2); // prints -5
Also note that I used >> instead of >>>. A >>> is an unsigned bitshift, while >> is signed.
System.out.println((-10) >>> 1); // prints 2147483643
@Mystical: I wrote a benchmark, that shows that the compiler / JVM doesn't do that optimization: https://ideone.com/aKDShA