RFR: 8336240: Test com/sun/crypto/provider/Cipher/DES/PerformanceTest.java fails with java.lang.ArithmeticException [v4]

[Bradford Wetmore]

On Fri, 19 Jul 2024 09:32:20 GMT, Fernando Guallini <fguallini at openjdk.org> wrote:

>> The manual test Cipher/DES/PerformanceTest.java fails with ArithmeticException due to potential division by zero. The issue arises when calculating the elapsed time using end - start, which could result in zero milliseconds if start and end are identical due to the high speed of execution. This leads to a division error in the following code snippet:
>> 
>> 
>> start = System.currentTimeMillis();
>> end = System.currentTimeMillis();
>> int speed = (int)((data.length * count)/(end - start));
>> 
>> This issue is easily reproducible on platforms where System.currentTimeMillis() has low granularity, such as many versions of Windows, end and start can be equal when obtaining System.currentTimeMillis() if the test runs very quickly.
>> 
>> The fix is to use System.nanoTime() instead, which is designed to measure elapsed time with very high precision. This value is then converted to microseconds so the tests can properly calculate the throughput (bytes processed per microsecond) for the report. Example output:
>> 
>> 
>> Algorithm                      DataSize Rounds Bytes/microsec
>> DES/ECB/NoPadding               1024    100       66
>> DES/ECB/NoPadding               1024    1000      50
>> DES/ECB/NoPadding               8192    100       70
>> DES/ECB/NoPadding               8192    1000      70
>> Average:                                            64
>
> Fernando Guallini has updated the pull request incrementally with one additional commit since the last revision:
> 
>   adding back the validation to avoid dividing by zero

Marked as reviewed by wetmore (Reviewer).

Alternatively, you could just add 1us and thus force it to be non-zero...it shouldn't affect the `speed` much.  Either way is fine.

-------------

PR Review: https://git.openjdk.org/jdk/pull/20135#pullrequestreview-2189115533
PR Comment: https://git.openjdk.org/jdk/pull/20135#issuecomment-2240039589