Impala Public Jenkins has submitted this change and it was merged. ( 
http://gerrit.cloudera.org:8080/9078 )

Change subject: IMPALA-6422: Use ldexp() instead of powf() in HLL.
......................................................................

IMPALA-6422: Use ldexp() instead of powf() in HLL.

Using ldexp() to compute a floating point power of two is
over 10x faster than powf().

This change is particularly helpful for speeding up
COMPUTE STATS TABLESAMPLE which has many calls to
HllFinalEstimate() where floating point power of two
computations are relevant.

Testing:
- core/hdfs run passed

Change-Id: I517614d3f9cf1cf56b15a173c3cfe76e0f2e0382
Reviewed-on: http://gerrit.cloudera.org:8080/9078
Reviewed-by: Alex Behm <[email protected]>
Tested-by: Impala Public Jenkins
---
M be/src/exec/incr-stats-util.cc
M be/src/exprs/aggregate-functions-ir.cc
M be/src/exprs/aggregate-functions.h
3 files changed, 9 insertions(+), 13 deletions(-)

Approvals:
  Alex Behm: Looks good to me, approved
  Impala Public Jenkins: Verified

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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: merged
Gerrit-Change-Id: I517614d3f9cf1cf56b15a173c3cfe76e0f2e0382
Gerrit-Change-Number: 9078
Gerrit-PatchSet: 5
Gerrit-Owner: Alex Behm <[email protected]>
Gerrit-Reviewer: Alex Behm <[email protected]>
Gerrit-Reviewer: Impala Public Jenkins
Gerrit-Reviewer: Tim Armstrong <[email protected]>
Gerrit-Reviewer: anujphadke <[email protected]>

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