From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: a07f3367d7,f00ac8eb01f056e8 X-Google-Attributes: gida07f3367d7,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,UTF8 Path: g2news2.google.com!news3.google.com!feeder.news-service.com!news.albasani.net!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail From: Simon Wright Newsgroups: comp.lang.ada Subject: Re: Interfacing Ada to C for linear algebra Date: Fri, 02 Sep 2011 15:53:03 +0100 Organization: A noiseless patient Spider Message-ID: References: <2cc811c2-e805-4407-8f2e-d1b5804782c9@i21g2000yqd.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: mx04.eternal-september.org; posting-host="dFCm8HWntFqmDIilBLqEJQ"; logging-data="21720"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX191Giul+8vB+r8hASlp4H/5D05+ys2UuN8=" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (darwin) Cancel-Lock: sha1:mjC02fBAyotca+9vZJtx833AH/g= sha1:3yI9xrH7+P3PnVuNYlc4nC0H23U= Xref: g2news2.google.com comp.lang.ada:21799 Date: 2011-09-02T15:53:03+01:00 List-Id: "vincent.diemunsch@gmail.com" writes: > Hello everybody, > > I would like to use in Ada some linear algebra libraries written in C, > especially the SuiteSparse : > http://www.cise.ufl.edu/research/sparse/SuiteSparse/ > These libraries handle Sparse Matrices that are in the format used > internally by MatLab : a column-compressed version of the standard > matrices. > > Ada defines Generic_Real_Arrays to handle vectors and matrices. So I > would like to simply create a Generic_Real_Sparse_Arrays package to > define MatLab compatible matrices. Since the internal format of MatLab > matrices is in C, in need to do a conversion between my Sparse_Matrix > and the C arrays that represent the Sparse Matrix in MatLab. > > Looking at the implementation of Generic_Real_Arrays in GNAT, I see > that they internally call the BLAS and LAPACK packages, written in > Fortran, through the use of two packages : System.Generic_Real_BLAS > and System.Generic_Real_LAPACK. These package do exactly the same as > what I want to do : they convert Ada arrays of Ada floating point type > in Fortran arrays of Fortran Float type and back, without using > copying, so that the compiler produces no code for this conversion > (using pragma Inline_Always and so on). This is important because if > we use optimized versions of linear algebra packages it is because we > manipulate huge arrays and we don't want to loose time in copying > values from on representation to another ! The LAPACK interface used in Generic_Real_Arrays deals with matrices in Ada (row-major) format and - usually, anyway - transposes in order to call the Fortran implementations. Unlike BLAS, LAPACK itself doesn't have options to deal with row-major matrices. We did some timings and found that it's quite a bit quicker to declare the BLAS/LAPACK interfaces in terms of Fortran (column-major) matrices (declared using pragma Convention (Fortran)) and have the compiler implement the necessary moves on assignment, rather than using a library Transpose subprogram. But make no mistake, the Generic_Real_Arrays code definitely copies! (look at the body for confirmation). > I suppose that since C is very common, there must already exist a very > good implementation of conversion of Ada arrays of floating point > types in C arrays of C.Float, idealy using the GNAT > implementation. This could save me a lot of time doing interfaces... GNAT and GCC share the same compiler backend, so the underlying numeric types are the same. Just tell the compiler what to import: procedure dgeev (Jobv_L : Character; Jobv_R : Character; N : Positive; A : in out Real_Arrays.Real_Matrix; Ld_A : Positive; W_R : out Real_Arrays.Real_Vector; W_I : out Real_Arrays.Real_Vector; V_L : out Real_Arrays.Real_Matrix; Ld_V_L : Integer; V_R : out Real_Arrays.Real_Matrix; Ld_V_R : Integer; Work : out Real_Arrays.Real_Vector; L_Work : Integer; Info : out Integer); pragma Import (Fortran, dgeev, "dgeev_"); (Real_Arrays.Real_Matrix etc from Generic_Real_Arrays). The Fortran convention means that the Character and Integer arguments are passed by reference without your needing to fake up accesses. More of this at https://sourceforge.net/projects/gnat-math-extn/ .