[Impala-CR](cdh5-trunk) IMPALA-2809: Improve scalar ByteSwap().

["Alex Behm (Code Review)" <ge...@cloudera.org>]

Hello Tim Armstrong,

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

    http://gerrit.cloudera.org:8080/3033

to look at the new patch set (#3).

Change subject: IMPALA-2809: Improve scalar ByteSwap().
......................................................................

IMPALA-2809: Improve scalar ByteSwap().

This patch improves our ByteSwap() function by handling
more byte sizes in the fast path, as opposed to the
loop-based slow path.

ByteSwap() is used heavily in when scanning Parquet decimals.

Before this patch, VTune showed ByteSwap() among the top
three worst cycle offenders when running TPCH-Q6 on my local
setup with a large lineitem table.

After this patch, ByteSwap() shows no significant contribution
to the overall cycles spent.

There was a measurable improvement of a few percent for TPCH-Q6.

Change-Id: I4f462e6bdb022db46b48889a6a7426120a80d9b4
---
M be/src/util/bit-util.h
A be/src/util/bit-util.inline.h
M be/src/util/decimal-util.h
3 files changed, 135 insertions(+), 29 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala refs/changes/33/3033/3
-- 
To view, visit http://gerrit.cloudera.org:8080/3033
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I4f462e6bdb022db46b48889a6a7426120a80d9b4
Gerrit-PatchSet: 3
Gerrit-Project: Impala
Gerrit-Branch: cdh5-trunk
Gerrit-Owner: Alex Behm <al...@cloudera.com>
Gerrit-Reviewer: Alex Behm <al...@cloudera.com>
Gerrit-Reviewer: Taras Bobrovytsky <tb...@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <ta...@cloudera.com>