RFR[S]:8241874 [PPC64] Improve performance of Long.reverseBytes() and Integer.reverseBytes() on Power9

[Corey Ashford]

On 4/2/20 7:27 AM, Michihiro Horie wrote:
> Hi Corey,
> 
> I’m not a reviewer, but I can run your benchmark in my local P9 node if 
> you share it.
> 
> Best regards,
> Michihiro

The tests are somewhat hokey; I added the shifts to keep the compiler 
from hoisting the code that it could predetermine the result.

Here's the one for Long.reverseBytes():

import java.lang.*;

class ReverseLong
{
     public static void main(String args[])
     {
         long reversed, re_reversed;
	long accum = 0;
	long orig = 0x1122334455667788L;
	long start = System.currentTimeMillis();
	for (int i = 0; i < 1_000_000_000; i++) {
		// Try to keep java from figuring out stuff in advance
		reversed = Long.reverseBytes(orig);
		re_reversed = Long.reverseBytes(reversed);
		if (re_reversed != orig) {
         		System.out.println("Orig: " + String.format("%16x", orig) + 
"  Re-reversed: " + String.format("%16x", re_reversed));
		}
		accum += orig;
		orig = Long.rotateRight(orig, 3);
	}
	System.out.println("Elapsed time: " + 
Long.toString(System.currentTimeMillis() - start));
	System.out.println("accum: " + Long.toString(accum));
     }
}


And the one for Integer.reverseBytes():

import java.lang.*;

class ReverseInt
{
     public static void main(String args[])
     {
         int reversed, re_reversed;
	int orig = 0x11223344;
	int accum = 0;
	long start = System.currentTimeMillis();
	for (int i = 0; i < 1_000_000_000; i++) {
		// Try to keep java from figuring out stuff in advance
		reversed = Integer.reverseBytes(orig);
		re_reversed = Integer.reverseBytes(reversed);
		if (re_reversed != orig) {
         		System.out.println("Orig: " + String.format("%08x", orig) + 
"  Re-reversed: " + String.format("%08x", re_reversed));
		}
		accum += orig;
		orig = Integer.rotateRight(orig, 3);
	}
	System.out.println("Elapsed time: " + 
Long.toString(System.currentTimeMillis() - start));
	System.out.println("accum: " + Integer.toString(accum));
     }
}