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8370057: Correct scale handling of BigDecimal.sqrt #27882

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8370057: Correct scale handling of BigDecimal.sqrt #27882

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JDK-8370057: Correct scale handling of BigDecimal.sqrt
jddarcy Oct 17, 2025
aa5d60f
Respond to review feedback.
jddarcy Oct 20, 2025
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6 changes: 3 additions & 3 deletions src/java.base/share/classes/java/math/BigDecimal.java
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
*
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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
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7 changes: 4 additions & 3 deletions test/jdk/java/math/BigDecimal/SquareRootTests.java
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Original file line number Diff line number Diff line change
@@ -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
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);

Expand Down