Hi, There is no objection for this proposal. Could you write this proposal to https://github.com/apache/arrow/issues/28497 too?
Then we can move forward (implement) this proposal. Thanks, -- kou In <CAJ+zOik5OnZ_6VAW5J_X4+3M2xvrJa7tbM=p9xx8qobaawd...@mail.gmail.com> "[DISCUSSION][C++] Re-proposal of 'divmod' in Compute Functions" on Sun, 9 Apr 2023 09:03:34 +0900, Hirokazu Suzuki <heronshoes...@gmail.com> wrote: > Hello all, > > This is a (re)proposal for a divmod kernel for the compute function. > This proposes the following two combinations of quotient and remainder for > 'divmod'. > > - [floor-quotient, modulo] > - [trunc-quotient, remainder] > > The first proposal for divmod was made in ARROW-12755 [1] and has been > discussed in GH-11116 [2], but has not yet been completed. > > On the other hand, the following relationships hold for the dividend, > quotient, divisor, > and modulo, > > quotient ∈ Ｚ > dividend = quotient * divisor + modulo, > |modulo| < |divisor| > > Since the sign of modulo is undefined in this expression, each language has > a different > behavior regarding the sign of the remainder when a negative number is > involved. > > For example, in C, C++, Go, Java, Rust, etc., the remainder will match the > sign > of the divisor. This is equivalent to performing a "truncation division to > zero: trunc" > when finding the quotient. > > On the other hand, R yields a remainder that matches the sign of the > divisor, > which is equivalent to performing "truncated division to infinity: floor" > when finding > the quotient. > > In addition, some languages provide both of these, such as Julia and Ruby. > > The following table lists the signs and operators for integer remainders. > > Table: Language, operator and operands > which sign is corresponding to the sign of remainder > > |Language |dividend |divisor | > |:--------|:-----------|:--------------| > | C | %, div | | > | C++ | %, div | | > | C# | % | | > | Go | % | | > | Java | % | Math.floorMod | > | Julia | rem | mod | > | MATLAB | rem | mod | > | Python | math.fmod | % | > | R | | %% | > | Ruby | remainder | %, modulo | > | Rust | % | | > | Scala | % | | > | Scheme | remainder | modulo | > | SQL | mod | | > > （The remainder of floating point numbers is omitted.） > > Since both styles exist, it is necessary to name and implement compute > functions > in a way avoiding confusion that may be used by many languages. > > So I propose to create two different divmods sets of quotient rounding > (trunc or floor) and remainders. > > - trunc_divmod ≡ [trunc_quotient, remainder] > - floor_divmod ≡ [floor_quotient, modulo] > > It is inconvenient without the kernel, at least for positive number. > So I put this proposal here to step the work forward. > > I am not an expert in this field and there may be some misunderstandings. > I would appreciate it if you could point out any mistakes. > > [1] https://issues.apache.org/jira/browse/ARROW-12755) > [2] https://github.com/apache/arrow/pull/11116) > > Best regards, > Hirokazu SUZUKI
