Fixup int overflow in reducers unit tests #3514
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Clang UBSan reports: core/unit_test/TestReducers.hpp:387:22: runtime error: signed integer overflow: 2038431744 * 3 cannot be represented in type 'int' core/unit_test/TestReducers.hpp:71:64: runtime error: signed integer overflow: 2038431744 * 3 cannot be represented in type 'int' core/unit_test/TestReducers.hpp:189:13: runtime error: signed integer overflow: 2038431744 * 3 cannot be represented in type 'int'
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(The unit test produces N random numbers between 1 and 4 and multiply them) |
core/unit_test/TestReducers.hpp
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| @@ -1020,7 +1020,7 @@ struct TestReducers { | |||
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| static void execute_integer() { | |||
| test_sum(10001); | |||
| test_prod(35); | |||
| test_prod(sizeof(Scalar) > 4 ? 35 : 19); // avoid int overflow | |||
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I would rather branch on the largest representable number such that
std::numeric_limits<Scalar>::max() > std::pow(4,n)
n < std::log(std::numeric_limits<Scalar>::max())/std::log(4);
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I can expand on the comment but your suggestion is imperfect too because it use knowledge of the fact test_prod generates random numbers between 1 and 4.
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For the record std::log(std::numeric_limits<int>::max())/std::log(4) is 15.5
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Yes, so why is 19 guaranteed to work?
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Retest this please |
crtrott
approved these changes
Oct 22, 2020
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Found along the way while working on #3512
Clang UBSan was reporting