Code Review Request, 8152237 Support BigInteger.TWO

[Peter Levart]

Ok, here's a test...

with just the following change:


diff -r 9ea9fb3c0c88 src/java.base/share/classes/java/math/BigInteger.java
--- a/src/java.base/share/classes/java/math/BigInteger.java     Wed Mar 
23 18:24:35 2016 +0100
+++ b/src/java.base/share/classes/java/math/BigInteger.java     Wed Mar 
23 19:55:01 2016 +0100
@@ -41,6 +41,7 @@
  import jdk.internal.math.DoubleConsts;
  import jdk.internal.math.FloatConsts;
  import jdk.internal.HotSpotIntrinsicCandidate;
+import jdk.internal.vm.annotation.Stable;

  /**
   * Immutable arbitrary-precision integers.  All operations behave as if
@@ -1213,8 +1214,10 @@
       * Initialize static constant array when class is loaded.
       */
      private static final int MAX_CONSTANT = 16;
-    private static BigInteger posConst[] = new BigInteger[MAX_CONSTANT+1];
-    private static BigInteger negConst[] = new BigInteger[MAX_CONSTANT+1];
+    @Stable
+    private static final BigInteger posConst[] = new 
BigInteger[MAX_CONSTANT+1];
+    @Stable
+    private static final BigInteger negConst[] = new 
BigInteger[MAX_CONSTANT+1];

      /**
       * The cache of powers of each radix.  This allows us to not have to



The results of simple benchmark:

/*

Original:

Benchmark                  Mode  Cnt  Score   Error  Units
BigIntegerBench.ONE        avgt   10  2.396 ± 0.232  ns/op
BigIntegerBench.valueOf_1  avgt   10  2.846 ± 0.233  ns/op
BigIntegerBench.valueOf_2  avgt   10  2.808 ± 0.054  ns/op

Patched:

Benchmark                  Mode  Cnt  Score   Error  Units
BigIntegerBench.ONE        avgt   10  2.381 ± 0.126  ns/op
BigIntegerBench.valueOf_1  avgt   10  2.347 ± 0.089  ns/op
BigIntegerBench.valueOf_2  avgt   10  2.323 ± 0.022  ns/op

*/
package jdk.test;

import org.openjdk.jmh.annotations.*;

import java.math.BigInteger;
import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime)
@Fork(1)
@Warmup(iterations = 5)
@Measurement(iterations = 10)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class BigIntegerBench {

     @Benchmark
     public BigInteger ONE() {
         return BigInteger.ONE;
     }

     @Benchmark
     public BigInteger valueOf_1() {
         return BigInteger.valueOf(1);
     }

     @Benchmark
     public BigInteger valueOf_2() {
         return BigInteger.valueOf(2);
     }
}


So, no need to change the API and all uses of valueOf(-MAX_CONSTANT <= i 
<= MAX_CONSTANT) for constant 'i' will be faster a bit.

Regards, Peter


On 03/23/2016 07:01 PM, Peter Levart wrote:
> Hi Xuelei,
>
> On 03/23/2016 04:26 AM, Xuelei Fan wrote:
>> Hi,
>>
>> Please review the update for the supporting of BigInteger.TWO:
>>
>> http://cr.openjdk.java.net/~xuelei/8152237/webrev/
>>
>> BigInteger.valueOf(2) is a common BigInteger value used in binary and 
>> cryptography operation calculation.  The BigInteger.TWO is not 
>> exported, and hence BigInteger.valueOf(2) is used instead in 
>> applications and JDK components.  The export of static BigInteger.TWO 
>> can improve performance and simplify existing code.
>>
>> Thanks,
>> Xuelei
>
> I think (haven't tried, just speculate) you could achieve the same 
> performance by:
>
> - adding final qualifier to static BigInteger.[posConst|negConst] fields
> - annotating those fields with @jdk.internal.vm.annotation.Stable 
> annotation
>
> This way BigInteger.valueOf(-MAX_CONSTANT <= i <= MAX_CONSTANT) when 
> called with a constant argument should fold into a constant when 
> compiled by JIT.
>
> The same optimization could be performed for valueOf methods of 
> java.lang.Byte, Character, Short, Integer & Long.
>
> @Stable annotation was a package-private annotation in 
> java.lang.invoke, reserved for method handles infrastructure, but has 
> since been made public and moved to a concealed package of java.base. 
> There is already a precedent for its use outside in java.lang.invoke: 
> in java.lang.String. For example:
>
> static final String s = ".....";
>
> s.charAt(0); // is folded into a constant by JIT
>
>
>
> Regards, Peter
>

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