On Dec 10, 12:39 am, Bill Hart <goodwillh...@googlemail.com> wrote:
> This is *fantastic* news that GotoBlas has been BSD licensed. I've
> wanted to use it in FLINT for years, and we've just been discussing
> highly optimised matrix routines (Fredrik Johansson has been writing
> lots of code too).
>
> But I am slightly confused over the CBLAS interface thing.
>
> It seems that the original BLAS reference implementation was in
> Fortran f77. In fact, a reference implementation seems to be provided,
> in Fortran, in the reference directory of GotoBlas. There is also some
> Fortran test code (presumably to compare the results of the optimised
> BLAS routines with the reference implementation). From what I can tell
> most of the GotoBLAS is implemented in C and assembly.
>
> From what I read here:
>
> http://www.inf.bv.tum.de/~heisserer/softwarelab04/doc/blas_report.pdf
>
> the usual problem is you have a BLAS written in Fortran, and you want
> to call it from C. So you have two options:
>
> 1) Link your C program against the BLAS (implemented in Fortran) and
> use the Fortran function names in your C program. (I'm unclear on
> whether some matrix transposes are also required.) This is possible
> because of a 1-1 correspondence between Fortran and C conventions.
> There's some name mangling required, Fortran calls by reference, and a
> few other differences with C.
>
> 2) Use a CBLAS implementation, which provides the same functionality,
> but with C function names and prototypes which wrap the original
> Fortran implementation. I understand such a CBLAS interface is
> provided by ATLAS. So one can link against libatlas and use the C
> function names without having to worry about the 1-1 correspondence
> with the Fortran code.
Sorry, that should say Fortran _interface_, not Fortran _code_. It
looks like the BLAS in ATLAS is _implemented_ in C and assembly and
provides both a Fortran and (proper) CBLAS _interface_. So it is also
an unusual BLAS in that it is not actually implemented in Fortran
itself.
>
> E.g:
>
> * using method 1 you'd have dgemm_("n", "n", &m ,&n ,&k ,&alpha,
> B[0],&ldb, A[0],&lda,&beta, C[0],&ldc); which calls the Fortran
> function directly from C, mangling everything appropriately.
>
> * using method 2 you'd have cblas_dgemm(Order, TransA, TransB, m, n,
> k, alpha, a, lda, b, ldb, beta, c, ldc); which calls the C function.
>
> So let's look at which GotoBLAS provides, by looking in it's CBlas
> interface, in the file cblas.h:
>
> void cblas_dgemm(enum CBLAS_ORDER Order, enum CBLAS_TRANSPOSE TransA,
> enum CBLAS_TRANSPOSE TransB, blasint M, blasint N, blasint K,
> double alpha, double *A, blasint lda, double *B, blasint ldb,
> double beta, double *C, blasint ldc);
>
> So what am I missing here?
>
> I also notice that much of the GotoBLAS functionality seems to be in
> (hand?) written assembly and C. That is, both the kernel and the
> (Fortran) interface actually seem to be implemented in C (Is this a
> case of: a determined programmer can write Fortran in any language?
> LOL.).
>
> Sorry if I am being completely ignorant here. I've never actually
> directly used ATLAS, GotoBLAS, f77 BLAS or CBLAS myself, as Sage just
> provides it for me, so I have no clue what I'm talking about. Is there
> additional functionality provided by a CBLAS interface not provided by
> Goto's BLAS? I did read somewhere that ATLAS provides some functions
> from LAPACK... ah yes, I think I have that right. That is on the ATLAS
> homepage. Do we use any of those?
>
> Anyhow, big +1 for using Goto if it is at all possible. I'm sure I'll
> certainly be using snippets of code from Goto in FLINT, assuming I can
> get the bits I need to compile without a Fortran compiler.
>
> Bill.
>
> On Dec 7, 11:42 pm, Francois Bissey <francois.bis...@canterbury.ac.nz>
> wrote:
>
>
>
>
>
>
>
> > Seems like I didn't dig deep enough.
>
> > So it isn't actively developed by the TACC
> > anymore, it is given to the community to
> > maintain and take over development.
>
> > It only provides f77blas. I guess it would
> > be possible to create a cblas interface using
> > f2c but it is not really something anyone would
> > want to maintain.
>
> > So unless someone can suggest an alternative
> > cblas implementation as well, gotoblas is not
> > a viable alternative.
>
> > Francois
>
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>
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>
> > winmail.dat
> > 3KViewDownload
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