[Runtime] optimize BigDecimal.divide

Summary: Use binary search in zero stripping of BigDecimal.divide Testing: jtreg Reviewers: Issue: https://github.com/dragonwell-project/dragonwell11/issues/ CR: https://github.com/dragonwell-project/dragonwell11/pull/
dragonwell-project · Jul 30, 2024 · d1d8c8f · d1d8c8f
1 parent 1811fb0
commit d1d8c8f
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diff --git a/src/hotspot/share/runtime/arguments.cpp b/src/hotspot/share/runtime/arguments.cpp
@@ -4115,6 +4115,10 @@ jint Arguments::parse(const JavaVMInitArgs* initial_cmd_args) {
     DumpAppCDSWithKlassId = true;
   }
 
+  if (UseBigDecimalOpt) {
+    PropertyList_add(&_system_properties, new SystemProperty("java.math.BigDecimal.opt", "true", true));
+  }
+
   // Set object alignment values.
   set_object_alignment();
 

diff --git a/src/hotspot/share/runtime/globals_ext.hpp b/src/hotspot/share/runtime/globals_ext.hpp
@@ -93,6 +93,9 @@
   product(bool, ReduceNMethodSize, false,                                   \
           "Move immutable data of nmethod out of code cache")               \
                                                                             \
+    product(bool, UseBigDecimalOpt, true,                                   \
+          "use binary search in zero stripping of BigDecimal")              \
+                                                                            \
   //add new AJDK specific flags here
 
 

diff --git a/src/java.base/share/classes/java/math/BigDecimal.java b/src/java.base/share/classes/java/math/BigDecimal.java
@@ -368,6 +368,16 @@ protected StringBuilderHelper initialValue() {
      */
     private static final BigDecimal ONE_HALF = valueOf(5L, 1);
 
+    private static boolean opt;
+    static {
+        try {
+            opt = Boolean.parseBoolean(System.getProperty("java.math.BigDecimal.optimization"));
+        } catch (SecurityException e) {
+            // When user define some secure environment, system property here may be inaccessible.
+            opt = false;
+        }
+    }
+
     // Constructors
 
     /**
@@ -4860,6 +4870,38 @@ private static boolean needIncrement(MutableBigInteger mdivisor, int roundingMod
         return commonNeedIncrement(roundingMode, qsign, cmpFracHalf, mq.isOdd());
     }
 
+    /**
+     * Remove insignificant trailing zeros from this
+     * {@code BigInteger} value until the preferred scale is reached or no
+     * more zeros can be removed. This is a faster version of createAndStripZerosToMatchScale
+     * using binary search instead of linear search.
+     *
+     * @return new {@code BigDecimal} with a scale possibly reduced
+     * to be closed to the preferred scale.
+     */
+    private static BigDecimal createAndStripZerosToMatchScaleFast(BigInteger intVal, int scale, long preferredScale) {
+        BigInteger qr[]; // quotient-remainder pair
+        int scaleStep;
+        while (intVal.compareMagnitude(BigInteger.TEN) >= 0
+                && scale > preferredScale) {
+            scaleStep = checkScale(intVal, Math.max(((long) scale - preferredScale) / 2, 1l));
+            if (intVal.getLowestSetBit() >= scaleStep) { // intVal can be divided by pow(10, scaleStep) only if intVal has more trailing zeros than scaleStep
+                qr = intVal.divideAndRemainder(bigTenToThe(scaleStep));
+                if (qr[1].signum() == 0) {
+                    intVal = qr[0];
+                    scale = checkScale(intVal, (long) scale - scaleStep); // could Overflow
+                    continue;
+                }
+            }
+            if (scaleStep == 1) {
+                break;
+            } else {
+                preferredScale = scale - scaleStep;
+            }
+        }
+        return valueOf(intVal, scale, 0);
+    }
+
     /**
      * Remove insignificant trailing zeros from this
      * {@code BigInteger} value until the preferred scale is reached or no
@@ -4870,6 +4912,9 @@ private static boolean needIncrement(MutableBigInteger mdivisor, int roundingMod
      * to be closed to the preferred scale.
      */
     private static BigDecimal createAndStripZerosToMatchScale(BigInteger intVal, int scale, long preferredScale) {
+        if (opt && preferredScale >= Integer.MIN_VALUE) {
+            return createAndStripZerosToMatchScaleFast(intVal, scale, preferredScale);
+        }
         BigInteger qr[]; // quotient-remainder pair
         while (intVal.compareMagnitude(BigInteger.TEN) >= 0
                && scale > preferredScale) {