RFR: 8074032: Instant.ofEpochMilli(millis).toEpochMilli() can throw arithmetic overflow in toEpochMilli()

[Daniel Fuchs]

Hi,

Please find below a patch for:

8074032: Instant.ofEpochMilli(millis).toEpochMilli() can
          throw arithmetic overflow in toEpochMilli()

http://cr.openjdk.java.net/~dfuchs/webrev_8074032/webrev.00/

The issue is that when converting milliseconds to seconds + nanos
Instant.ofEpochMilli() uses floorDiv and floorMod, as it should.
This means that for negative values of 'millis' then seconds will
be millis/1000 - 1,  and nanos will be positive.

When converting back to epoch millis, if multiplyExact is used
without precaution, then (millis/1000 -1) * 1000 may not fit in
a long. The solution is thus to compute ((millis/1000 -1) +1) * 1000
instead and then add (nanos - 1000) to the result.


Note: this issue is causing some JCK tests that call
LogRecord.setMillis(Long.MIN_VALUE) to fail.

best regards,

-- daniel