@kou Thank you for the comment. I will create issue about this. 2023年5月10日(水) 9:43 Sutou Kouhei <k...@clear-code.com>:
> 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 >
