[C++] Decimal32 support introduced an UBSAN error

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

GH-43957 introduced the following UBSAN error:

https://github.com/apache/arrow/actions/runs/11114266653/job/30880385337#step:6:4315

[ RUN ] Decimal32Test.LeftShift
/arrow/cpp/src/arrow/util/decimal_test.cc:1727:33: runtime error: left shift of 123 by 30 places cannot be represented in type 'int32_t' (aka 'int')
 #0 0x562b6abc3a04 in arrow::Decimal32Test_LeftShift_Test::TestBody()::$_0::operator()(int, unsigned int) const /arrow/cpp/src/arrow/util/decimal_test.cc:1727:33
 #1 0x562b6abbe4a3 in arrow::Decimal32Test_LeftShift_Test::TestBody() /arrow/cpp/src/arrow/util/decimal_test.cc:1741:3
 #2 0x7fc0d8b24e7e in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) (/usr/local/lib/libarrow_testing.so.1800+0x106de7e) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #3 0x7fc0d8b19935 in testing::Test::Run() (/usr/local/lib/libarrow_testing.so.1800+0x1062935) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #4 0x7fc0d8b19ab4 in testing::TestInfo::Run() (/usr/local/lib/libarrow_testing.so.1800+0x1062ab4) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #5 0x7fc0d8b1a068 in testing::TestSuite::Run() (/usr/local/lib/libarrow_testing.so.1800+0x1063068) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #6 0x7fc0d8b1a76e in testing::internal::UnitTestImpl::RunAllTests() (/usr/local/lib/libarrow_testing.so.1800+0x106376e) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #7 0x7fc0d8b25446 in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) (/usr/local/lib/libarrow_testing.so.1800+0x106e446) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #8 0x7fc0d8b19b7b in testing::UnitTest::Run() (/usr/local/lib/libarrow_testing.so.1800+0x1062b7b) (BuildId: 118793bf888d7168cdf3c1fc75787526ccb324c5)
 #9 0x562b6b6576ed in RUN_ALL_TESTS() /usr/include/gtest/gtest.h:2490:46
 #10 0x562b6b657639 in main /arrow/cpp/src/arrow/util/logging_test.cc:129:10
 #0 0x7fc0b6b43d8f in
 #12 0x7fc0b6b43e3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e3f) (BuildId: 490fef8403240c91833978d494d39e537409b92e)
 #13 0x562b6a697dc4 in _start (/build/cpp/debug/arrow-utility-test+0x13fddc4) (BuildId: aaabec8f2b98a2f0267cb51501c0340b2eec22e2)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /arrow/cpp/src/arrow/util/decimal_test.cc:1727:33 in
/build/cpp/src/arrow/util

Component(s)

C++

[kou]

@zeroshade Could you take a look at this?

[zeroshade]

Damnit I thought I got all of them. I'll take care of it

[zeroshade]

Fixed by #44280