Skip to content

8370057: Correct scale handling of BigDecimal.sqrt #27882

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 2 commits into from
Closed

8370057: Correct scale handling of BigDecimal.sqrt #27882

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
2393649
JDK-8370057: Correct scale handling of BigDecimal.sqrt
jddarcy Oct 17, 2025
aa5d60f
Respond to review feedback.
jddarcy Oct 20, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
7 changes: 4 additions & 3 deletions src/java.base/share/classes/java/math/BigDecimal.java
View file
Open in desktop
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 +2174,8 @@ 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 = this.scale/2;
final int preferredScale = Math.ceilDiv(this.scale, 2);

BigDecimal result;
if (mc.roundingMode == RoundingMode.UNNECESSARY || mc.precision == 0) { // Exact result requested
Expand Down
5 changes: 3 additions & 2 deletions test/jdk/java/math/BigDecimal/SquareRootTests.java
View file
Open in desktop
Original file line number Diff line number Diff line change
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