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Date: Wed, 1 Mar 2017 18:06:02 +0000
From: "Dan Hecht (Code Review)" <gerrit@cloudera.org>
To: Zach Amsden <zamsden@cloudera.com>, impala-cr@cloudera.com,
        reviews@impala.incubator.apache.org
CC: Michael Ho <kwho@cloudera.com>
Reply-To: dhecht@cloudera.com
Subject: =?UTF-8?Q?=5BImpala-ASF-CR=5D_IMPALA-4813=3A_Round_on_divide_and_multiply=0A?=
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archived-at: Wed, 01 Mar 2017 18:06:08 -0000

Dan Hecht has posted comments on this change.

Change subject: IMPALA-4813: Round on divide and multiply
......................................................................


Patch Set 8:

(2 comments)

http://gerrit.cloudera.org:8080/#/c/6132/8/be/src/runtime/decimal-test.cc
File be/src/runtime/decimal-test.cc:

Line 635:             result_scale);
> Are you sure you didn't miss the max(6, t1.scale + t2.precision + 1) above?
When the desired result precision is > 38, the java code reduces both precision and scale (see createAdjustedDecimalType()).  This code only reduces precision.

A simple example that would show the difference is:

DECIMAL(38,38) / DECIMAL(38,38).

The java code will give DECIMAL(38,6).  This code will give:

result_scale = min(38, max(6, 38 + 38 + 1)) = 38
result_prec = min(38, 38 - 38 + 38 + 38) = 38
i.e. DECIMAL(38, 38).


http://gerrit.cloudera.org:8080/#/c/6132/8/be/src/runtime/decimal-value.inline.h
File be/src/runtime/decimal-value.inline.h:

Line 350:     DCHECK(sizeof(RESULT_T) > 8 || abs(r) <= DecimalUtil::MAX_UNSCALED_DECIMAL8);
> That is what I was trying to say.
How about using the DCHECK I wrote out then, to be clear about this?


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Gerrit-MessageType: comment
Gerrit-Change-Id: Ie6bfcbe37555b74598d409c6f84f06b0ae5c4312
Gerrit-PatchSet: 8
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Zach Amsden <zamsden@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dhecht@cloudera.com>
Gerrit-Reviewer: Michael Ho
Gerrit-Reviewer: Michael Ho <kwho@cloudera.com>
Gerrit-Reviewer: Zach Amsden <zamsden@cloudera.com>
Gerrit-HasComments: Yes