[GitHub] [arrow] cyb70289 commented on pull request #10274: ARROW-12685: [C++][Compute] Add unary absolute value kernel

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cyb70289 commented on pull request #10274:
URL: https://github.com/apache/arrow/pull/10274#issuecomment-840269487


   Thanks @edponce for deep investigation.
   
   From std::abs() [document](https://en.cppreference.com/w/cpp/numeric/math/abs), it is *UB* if input is `numeic_limit::min()`. So compiler can do whatever optimization that doesn't violate the standard.
   
   `Computes the absolute value of an integer number. The behavior is undefined if the result cannot be represented by the return type. `
   
   For checked abs, you can check `arg == min()` before calling `std::abs()`.
   For non-checked abs, thought compiler generated code is safe, I think it's better to go back to `return v < 0 ? (~(unsigned)v + 1) : v;` approach.


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