8183912: java.math.BigDecimal.movePointLeft() should return this if called with zero argument

[Brian Burkhalter]

https://bugs.openjdk.java.net/browse/JDK-8183912 
<https://bugs.openjdk.java.net/browse/JDK-8183912>

For the patch included below, the JMH benchmark MovePointLeftZero attached to 
the above issue, when run with options "-f 1 -wi 5 -w 5 -i 10 -r 10" (one fork, 
five warmup iterations of five seconds each, ten measurement iterations of ten 
seconds each), shows an order of magnitude (10X) throughput improvement for a 
zero left shift. The effect on the positive left shift case appears to be at 
the level of measurement noise.

Thanks,

Brian

--- a/src/java.base/share/classes/java/math/BigDecimal.java
+++ b/src/java.base/share/classes/java/math/BigDecimal.java
@@ -2871,6 +2871,8 @@
      * @throws ArithmeticException if scale overflows.
      */
     public BigDecimal movePointLeft(int n) {
+        if (n == 0) return this;
+
         // Cannot use movePointRight(-n) in case of n==Integer.MIN_VALUE
         int newScale = checkScale((long)scale + n);
         BigDecimal num = new BigDecimal(intVal, intCompact, newScale, 0);
@@ -2893,6 +2895,8 @@
      * @throws ArithmeticException if scale overflows.
      */
     public BigDecimal movePointRight(int n) {
+        if (n == 0) return this;
+
         // Cannot use movePointLeft(-n) in case of n==Integer.MIN_VALUE
         int newScale = checkScale((long)scale - n);
         BigDecimal num = new BigDecimal(intVal, intCompact, newScale, 0);