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From "Jim Apple (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-4939, IMPALA-4940: Decimal V2 multiplication
Date Wed, 27 Sep 2017 20:31:02 GMT
Jim Apple has posted comments on this change. ( http://gerrit.cloudera.org:8080/7438 )

Change subject: IMPALA-4939, IMPALA-4940: Decimal V2 multiplication
......................................................................


Patch Set 6:

> I totally agree about doing anything fancy as a followup.  In
 > particular, I did not find anything at all useful in AVX to help. 
 > There is no vectored multiply large enough for this, and FMA
 > operations won't help either as they basically only help with
 > precision loss on floating point types.
 > 
 > Considering the perf difference is so extreme in some cases, I
 > think we should strongly consider either living with the broken
 > behavior until we can come up with a solution, or else verifying
 > with users making use of the DECIMAL_V2 feature that this will not
 > be a problem.

AVX2 has 32x8 times 32x8 multiplication. I have elsewhere simulated 64-bit multiplication
with this, combines with additions and shifts, and received a speedup on 64x4 times 64x4 operations.


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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I37ad6232d7953bd75c18dc86e665b2b501a1ebe1
Gerrit-Change-Number: 7438
Gerrit-PatchSet: 6
Gerrit-Owner: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Gerrit-Reviewer: Dan Hecht <dhecht@cloudera.com>
Gerrit-Reviewer: Jim Apple <jbapple-impala@apache.org>
Gerrit-Reviewer: Michael Ho <kwho@cloudera.com>
Gerrit-Reviewer: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>
Gerrit-Reviewer: Zach Amsden <zamsden@cloudera.com>
Gerrit-Comment-Date: Wed, 27 Sep 2017 20:31:02 +0000
Gerrit-HasComments: No

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