8341402: BigDecimal's square root optimization

src/java.base/share/classes/java/math/BigDecimal.java

@@ -2247,7 +2247,7 @@ public BigDecimal sqrt(MathContext mc) {
                         || mc.roundingMode == RoundingMode.HALF_EVEN && sqrt.testBit(0)
                         // Check if remainder is non-zero
                         || !workingInt.equals(workingSqrt.multiply(workingSqrt))
-                        || working.compareTo(new BigDecimal(workingInt)) != 0) {
+                        || !working.isInteger()) {
                     increment = true;
                 }
             }
@@ -2262,7 +2262,7 @@ public BigDecimal sqrt(MathContext mc) {
                 BigInteger[] sqrtRem = workingInt.sqrtAndRemainder();
                 sqrt = sqrtRem[0];
                 // Check if remainder is non-zero
-                if (sqrtRem[1].signum != 0 || working.compareTo(new BigDecimal(workingInt)) != 0)
+                if (sqrtRem[1].signum != 0 || !working.isInteger())
                     sqrt = sqrt.add(1L);
             }
 
@@ -3475,6 +3475,14 @@ private static String getValueString(int signum, String intString, int scale) {
         return buf.toString();
     }
 
+    /**
+     * @return {@code true} if and only if {@code this == this.toBigInteger()}
+     */
+    boolean isInteger() {
+        return scale <= 0 || signum() == 0
+                || stripZerosToMatchScale(intVal, intCompact, scale, 0L).scale == 0;
+    }
+
     /**
      * Converts this {@code BigDecimal} to a {@code BigInteger}.
      * This conversion is analogous to the

test/jdk/java/math/BigDecimal/SquareRootTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 4851777 8233452
+ * @bug 4851777 8233452 8341402
  * @summary Tests of BigDecimal.sqrt().
  */