Review Request 124539: Refactor KDevHash to use boost::hash_combine approach internally.

[Milian Wolff]

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https://git.reviewboard.kde.org/r/124539/
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(Updated Aug. 2, 2015, 2:16 p.m.)


Review request for KDevelop.


Repository: kdevplatform


Description (updated)
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Instead of hashing every byte of an integral type individually,
we leverage qHash and boost::hash_combine to create an overall
hash. The result should be just as good, as it's proven technology,
but the hash functions themselves become much faster. This is
demonstrated by the newly added benchmark.

Before:

    ********* Start testing of TestKDevHash *********
    Config: Using QtTest library 5.5.0, Qt 5.5.0 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.1.0)
    PASS   : TestKDevHash::initTestCase()
    PASS   : TestKDevHash::benchHash_int()
    RESULT : TestKDevHash::benchHash_int():
         0.075 msecs per iteration (total: 77, iterations: 1024)
    PASS   : TestKDevHash::benchHash_uint()
    RESULT : TestKDevHash::benchHash_uint():
         0.075 msecs per iteration (total: 77, iterations: 1024)
    PASS   : TestKDevHash::benchHash_quint64()
    RESULT : TestKDevHash::benchHash_quint64():
         0.15 msecs per iteration (total: 77, iterations: 512)
    PASS   : TestKDevHash::benchHash_bool()
    RESULT : TestKDevHash::benchHash_bool():
         0.018 msecs per iteration (total: 77, iterations: 4096)
    PASS   : TestKDevHash::cleanupTestCase()
    Totals: 6 passed, 0 failed, 0 skipped, 0 blacklisted
    ********* Finished testing of TestKDevHash *********

After:

    ********* Start testing of TestKDevHash *********
    Config: Using QtTest library 5.5.0, Qt 5.5.0 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.1.0)
    PASS   : TestKDevHash::initTestCase()
    PASS   : TestKDevHash::benchHash_int()
    RESULT : TestKDevHash::benchHash_int():
         0.0244 msecs per iteration (total: 100, iterations: 4096)
    PASS   : TestKDevHash::benchHash_uint()
    RESULT : TestKDevHash::benchHash_uint():
         0.024 msecs per iteration (total: 99, iterations: 4096)
    PASS   : TestKDevHash::benchHash_quint64()
    RESULT : TestKDevHash::benchHash_quint64():
         0.025 msecs per iteration (total: 53, iterations: 2048)
    PASS   : TestKDevHash::benchHash_bool()
    RESULT : TestKDevHash::benchHash_bool():
         0.020 msecs per iteration (total: 85, iterations: 4096)
    PASS   : TestKDevHash::cleanupTestCase()
    Totals: 6 passed, 0 failed, 0 skipped, 0 blacklisted
    ********* Finished testing of TestKDevHash *********

REVIEW: 124539


Diffs
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  CMakeLists.txt 70174433c9d9b88595254887c4f06c12aa7043e0 
  language/CMakeLists.txt 2c2b0285b68d209e07af185c43dcf157507f5a54 
  language/util/kdevhash.h 40c32935aec9c7e5552769e780c033e96cf63166 
  language/util/tests/CMakeLists.txt PRE-CREATION 
  language/util/tests/test_kdevhash.cpp PRE-CREATION 
  plugins/projectfilter/projectfilter.h 014e5a1eabbb3a2d9e71baeee3e38643cb8649e7 
  serialization/tests/test_indexedstring.cpp f0c7958ac33c6fc6c4febbaa106e0ca30f8a60f8 

Diff: https://git.reviewboard.kde.org/r/124539/diff/


Testing (updated)
-------

compiled and ran tests, everything seems to work fine


Thanks,

Milian Wolff

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