JDK-8253409 : Double-rounding possibility in float fma
- Type: Bug
- Component: core-libs
- Sub-Component: java.lang
- Affected Version: 11,15
- Priority: P4
- Status: Closed
- Resolution: Fixed
- OS: generic
- CPU: generic
- Submitted: 2020-09-21
- Updated: 2021-03-22
- Resolved: 2021-02-23
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Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.
To download the current JDK release, click here.
| JDK 11 | JDK 13 | JDK 16 | JDK 17 |
|---|---|---|---|
| 11.0.11-oracleFixed | 13.0.7Fixed | 16.0.1Fixed | 17 b11Fixed  |
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Relates :
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Description
ADDITIONAL SYSTEM INFORMATION :
Ubuntu 18.04 on x86_64
$ java -version
openjdk version "11.0.8" 2020-07-14
OpenJDK Runtime Environment (build 11.0.8+10-post-Ubuntu-0ubuntu118.04.1)
OpenJDK 64-Bit Server VM (build 11.0.8+10-post-Ubuntu-0ubuntu118.04.1, mixed mode, sharing)
A DESCRIPTION OF THE PROBLEM :
I found Math.fma(float, float, float) method returned different values with or without -XX:-UseFMA VM option for the same inputs.
STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Save the code as FMAExample.java
2. Run `javac FMAExample.java`
3. Run `java -XX:-UseFMA FMAExample`
EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Step 3 prints out 0x1.000002p52
ACTUAL -
Step 3 printed out 0x1.000004p52
---------- BEGIN SOURCE ----------
public class FMAExample {
public static void main(String[] args) {
float a = 0x1.fffffep23f;
float b = 0x1.000004p28f;
float c = 0x1.fep5f;
// The below line prints out different values for +/-UseFMA option.
// -XX:+UseFMA: 0x1.000002p52
// -XX:-UseFMA: 0x1.000004p52
System.out.printf("%a\n", Math.fma(a, b, c));
}
}
---------- END SOURCE ----------
CUSTOMER SUBMITTED WORKAROUND :
Do not specify `java -XX:-UseFMA FMAExample`
Comments
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