How is the modulo operator implemented in the HotSpot JVM?

Question

I understand that the modulus operation can be optimised using a little & wise magic where the divisor is a power of 2...

• and presuma

Answer 1

I spent some time on this very question, writing this blog post with all the details.

In short:

• The HotSpot JDK 1.8 irem (mod int) is ~20% slower than the n & (pow2-1) trick
• The HotSpot JDK 1.8 frem (mod float) is 3x slower
• You mileage varies based on JIT passes, so the benefit for Int's is minimal

So, there is a clear benefit to not do mod on Doubles, and you might get some benefit with Natural Integer Dividends and power of 2 Divisors.