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Date: Tue, 28 Feb 2017 23:58:46 +0000
From: "Zach Amsden (Code Review)" <gerrit@cloudera.org>
To: impala-cr@cloudera.com, reviews@impala.incubator.apache.org
CC: Dan Hecht <dhecht@cloudera.com>, Michael Ho <kwho@cloudera.com>
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Subject: =?UTF-8?Q?=5BImpala-ASF-CR=5D_IMPALA-4813=3A_Round_on_divide_and_multiply=0A?=
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archived-at: Tue, 28 Feb 2017 23:58:50 -0000

Zach Amsden has posted comments on this change.

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


Patch Set 5:

(9 comments)

http://gerrit.cloudera.org:8080/#/c/6132/2/be/src/exprs/decimal-operators-ir.cc
File be/src/exprs/decimal-operators-ir.cc:

PS2, Line 729: \
> ROUND && ?
I thought I already got rid of this, it's not needed.


http://gerrit.cloudera.org:8080/#/c/6132/5/be/src/runtime/decimal-value.inline.h
File be/src/runtime/decimal-value.inline.h:

PS5, Line 194: namespace detail {
> Why new namespace ? To avoid name collision ?
Yeah, even though this is "inline.h", this is still a private implementation detail.


PS5, Line 203: DCHECK(multiplier > 1);
> DCHECK(multiplier > 0 && multiplier % 2 == 0);
We still want multiplier > 1, since delta_scale > 0


PS5, Line 205: RESULT_T result = value / multiplier;
> Please consider hoisting this out of the loop so we don't need the else sta
Done


PS5, Line 208: a multiple of two.
> Should there be a DCHECK for this ? See comment above.
Done


PS5, Line 249:   // Check overflow again after rounding since +/-1 could cause decimal overflow
             :   if (result_precision == ColumnType::MAX_PRECISION) {
             :     *overflow |= abs(result) > DecimalUtil::MAX_UNSCALED_DECIMAL16;
> Should this be inside the if-stmt above ? I don't see any rounding outside 
Done


PS5, Line 285:   // Check overflow again after rounding since +/-1 could cause decimal overflow
             :   if (result_precision == ColumnType::MAX_PRECISION) {
             :     *overflow |= abs(result) > DecimalUtil::MAX_UNSCALED_DECIMAL16;
> Should this be inside the if-stmt above ? I don't see any rounding outside 
Done


PS5, Line 314:  if (round) {
> Should we skip this if *overflow is true ?
probably not worth it.  If things can inline, we may start computing x % y before overflow's value is known, so we may get better code.


PS5, Line 316:  free
             :       // free
> duplicated "free"
Done


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Gerrit-MessageType: comment
Gerrit-Change-Id: Ie6bfcbe37555b74598d409c6f84f06b0ae5c4312
Gerrit-PatchSet: 5
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