Tim Armstrong has posted comments on this change. ( 
http://gerrit.cloudera.org:8080/8329 )

Change subject: IMPALA-4964: Fix Decimal modulo overflow
......................................................................


Patch Set 2:

(2 comments)

Looks good, just a couple of things that could be clarified.

http://gerrit.cloudera.org:8080/#/c/8329/1/be/src/exprs/expr-test.cc
File be/src/exprs/expr-test.cc:

http://gerrit.cloudera.org:8080/#/c/8329/1/be/src/exprs/expr-test.cc@2286
PS1, Line 2286:   // Test modulo operator
It would be helpful to comment that (-x) % y == -(x % y) to make it easier to 
understand the results (I was initially confused about how negative modulo 
should be handled).

(I found this explanation helpful: https://stackoverflow.com/a/1907723)

I find negative numbers on the RHS of the modulo even more confusing so it 
might help to have a similar clarification.


http://gerrit.cloudera.org:8080/#/c/8329/2/be/src/runtime/decimal-value.inline.h
File be/src/runtime/decimal-value.inline.h:

http://gerrit.cloudera.org:8080/#/c/8329/2/be/src/runtime/decimal-value.inline.h@505
PS2, Line 505:   // inputs to int256_t.
Maybe briefly mention that we want to avoid int256_t is very slow - it's 
obvious to us now but might help a future reader of the code.



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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I5420201d4440d421e33e443df005cdcc16b8a6cd
Gerrit-Change-Number: 8329
Gerrit-PatchSet: 2
Gerrit-Owner: Taras Bobrovytsky <[email protected]>
Gerrit-Reviewer: Michael Ho <[email protected]>
Gerrit-Reviewer: Taras Bobrovytsky <[email protected]>
Gerrit-Reviewer: Tim Armstrong <[email protected]>
Gerrit-Reviewer: Zach Amsden <[email protected]>
Gerrit-Reviewer: anujphadke <[email protected]>
Gerrit-Comment-Date: Tue, 24 Oct 2017 00:13:21 +0000
Gerrit-HasComments: Yes

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