[Impala-ASF-CR] IMPALA-5668: Fix cast(X as timestamp) for negative subsecond Decimals

["Csaba Ringhofer (Code Review)" <ge...@cloudera.org>]

Hello Lars Volker, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/8051

to look at the new patch set (#2).

Change subject: IMPALA-5668: Fix cast(X as timestamp) for negative subsecond Decimals
......................................................................

IMPALA-5668: Fix cast(X as timestamp) for negative subsecond Decimals

The timestamp conversion from negative fractional Decimal types
(interpreted as unix timestamp) was wrong - the whole part
was rounded toward zero, and fractional part was being added
instead of being subtracted.

Example for the wrong behaivour:
+-------------------------------------------------+
| cast(cast(-0.1 as decimal(20,10)) as timestamp) |
+-------------------------------------------------+
| 1970-01-01 00:00:00.100000000                   |
+-------------------------------------------------+
while casting to double works correctly:
+-----------------------------------------+
| cast(cast(-0.1 as double) as timestamp) |
+-----------------------------------------+
| 1969-12-31 23:59:59.900000000           |
+-----------------------------------------+

Change-Id: I8216f4c0f100c1bd68891cd6048236bfe4c205f0
---
M be/src/exprs/decimal-operators-ir.cc
M be/src/exprs/expr-test.cc
2 files changed, 9 insertions(+), 0 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/51/8051/2
-- 
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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I8216f4c0f100c1bd68891cd6048236bfe4c205f0
Gerrit-Change-Number: 8051
Gerrit-PatchSet: 2
Gerrit-Owner: Csaba Ringhofer <cs...@cloudera.com>
Gerrit-Reviewer: Lars Volker <lv...@cloudera.com>