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From "Zach Amsden (Code Review)" <>
Subject [Impala-ASF-CR] IMPALA-2020: Add rounding for decimal casts
Date Mon, 13 Feb 2017 23:51:37 GMT
Zach Amsden has posted comments on this change.

Change subject: IMPALA-2020: Add rounding for decimal casts

Patch Set 5:

File be/src/exprs/

PS5, Line 303: return to_type(dv.whole_part(scale)); 
> any reason not to have ToInt<>() handle this case too by passing in 'round'
Not really - I thought the saner behavior for ToInt was rounding and wrote this cast first,
which didn't require a parameter, whereas FromDouble does as it is used in places where no
context is available.  I can add this if you think it is useful.
File be/src/exprs/

Line 185:         value_.decimal4_val = Decimal4Value::FromDouble(type, v, &overflow,
> where is this used? will it break compatibility?
In what sense?
File be/src/runtime/decimal-value.h:

PS5, Line 54: bool* overflow,
            :       bool round
> here and below, let's keep input parameters first, then output params.
Done.  Means I can't give a default value to round unless I also give a default value to overflow,
but lets do that anyway.

Is it okay if I change the ABI here to be

>From Double (const ColumnType& t, double d, bool round = true, bool& overflow
= of_ignored)

and then have a static bool DecimalValue::of_ignored which will get inserted when the caller
doesn't bother to check overflow.  (Actually, Q: can reference arguments even have default
values?)  The reason being to prevent a nullptr deref crash.  Worth having a debate about
references vs. pointers here.  Passing a pointer allows us to omit the overflow check from
ever happening (ptr == nullptr should be known at compile time) but we currently don't do
that or null checks in any of the places where we pass back this style of overflow.  I think
we probably will want the overflow check in all runtime cases so maybe this doesn't matter.

Line 232:   inline typename RESULT_T::underlying_type_t ToInt(int scale, bool& overflow)
> add a function comment.

PS5, Line 232:  bool& overflow
> use 'bool* overflow'. we generally use pointers for output params to make i
You have answered my last question.  Please ignore
File be/src/runtime/decimal-value.inline.h:

Line 50:     if (abs(d) >= max_value) {
> is this correct? 'd' is already scaled here.  please be sure to test the up
Yeah that is bogus.  What we need is the maximum integer value that represents a base 10 number
of length precision, so the -scale should go.

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Gerrit-MessageType: comment
Gerrit-Change-Id: I2daf186b4770a022f9cb349d512067a1dd624810
Gerrit-PatchSet: 5
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Zach Amsden <>
Gerrit-Reviewer: Dan Hecht <>
Gerrit-Reviewer: Michael Ho
Gerrit-Reviewer: Zach Amsden <>
Gerrit-HasComments: Yes

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