8370057: Correct scale handling of BigDecimal.sqrt

Reviewed-by: rgiulietti

Author: jddarcy

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

@@ -154,7 +154,7 @@
  * <tr><th scope="row">Subtract</th><td>max(minuend.scale(), subtrahend.scale())</td>
  * <tr><th scope="row">Multiply</th><td>multiplier.scale() + multiplicand.scale()</td>
  * <tr><th scope="row">Divide</th><td>dividend.scale() - divisor.scale()</td>
- * <tr><th scope="row">Square root</th><td>radicand.scale()/2</td>
+ * <tr><th scope="row">Square root</th><td>ceil(radicand.scale()/2.0)</td>
  * </tbody>
  * </table>
  *
@@ -2113,7 +2113,7 @@ public BigDecimal[] divideAndRemainder(BigDecimal divisor, MathContext mc) {
      * with rounding according to the context settings.
      *
      * <p>The preferred scale of the returned result is equal to
-     * {@code this.scale()/2}. The value of the returned result is
+     * {@code Math.ceilDiv(this.scale(), 2)}. The value of the returned result is
      * always within one ulp of the exact decimal value for the
      * precision in question.  If the rounding mode is {@link
      * RoundingMode#HALF_UP HALF_UP}, {@link RoundingMode#HALF_DOWN
@@ -2174,7 +2174,7 @@ public BigDecimal sqrt(MathContext mc) {
 
         // The code below favors relative simplicity over checking
         // for special cases that could run faster.
-        final int preferredScale = this.scale/2;
+        final int preferredScale = Math.ceilDiv(this.scale, 2);
 
         BigDecimal result;
         if (mc.roundingMode == RoundingMode.UNNECESSARY || mc.precision == 0) { // Exact result requested

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2025, 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
@@ -348,7 +348,7 @@ private static int lowPrecisionPerfectSquares() {
 
             for (int scale = 0; scale <= 4; scale++) {
                 BigDecimal scaledSquare = square.setScale(scale, RoundingMode.UNNECESSARY);
-                int expectedScale = scale/2;
+                int expectedScale = Math.ceilDiv(scale, 2);
                 for (int precision = 0; precision <= 5; precision++) {
                     for (RoundingMode rm : RoundingMode.values()) {
                         MathContext mc = new MathContext(precision, rm);
@@ -582,7 +582,8 @@ public static BigDecimal sqrt(BigDecimal bd, MathContext mc) {
                 // The code below favors relative simplicity over checking
                 // for special cases that could run faster.
 
-                int preferredScale = bd.scale()/2;
+                int preferredScale = Math.ceilDiv(bd.scale(), 2);
+
                 BigDecimal zeroWithFinalPreferredScale =
                     BigDecimal.valueOf(0L, preferredScale);