guile-ffi-cblas

guile-ffi-cblas

This is a set of Guile FFI bindings for CBLAS, the library of linear algebra subprograms¹.

To use the bindings, import (ffi cblas). CBLAS will be loaded from the default dynamic library path (see ‘Installation notes’ below). There are up to three bindings for each function, here using ZGEMM as an example:

• cblas_zgemm (raw binding): the raw C function by pointer->procedure. Don't use this if you aren't familiar with Guile's FFI.

• zgemm! (typed binding): takes array arguments of type 'c64 and operates by effect, without making copies. All the arguments must be properly sized. The return value is unspecified.

• zgemm (functional binding): takes array arguments of compatible types and returns a newly constructed array. The arguments will be converted as necessary, which may result in copies. The returned array will be of 'c64 type.

In principle, for the last two bindings, you don't need to care whether your array is row-major or column-major or what the strides are. The bindings will extract the required strides from the array arguments. However, since CBLAS doesn't support arbitrary strides (e.g. it only supports a column stride for matrix arguments, assuming column-major order), some array arguments will cause the typed binding to fail, or result in extra copies with the functional binding.

If the function doesn't return an array (e.g. sdot) then we only provide two bindings (e.g. cblas_sdot and sdot).

Enter ,help (ffi cblas) at the Guile REPL to list all the bindings available².

Note that this package is a work in progress and that there are bugs. For example, negative strides require specific handling for CBLAS and are not supported yet.

Installation notes

guile-ffi-cblas uses dynamic-link to load the dynamic libraries for CBLAS. To do this, the names of the respective library files must be known. The default name libcblas can be configured with the environment variable GUILE_FFI_CBLAS_LIBNAME. Some alternative names that I've seen are libblas or libatlas.

If your CBLAS libraries are not installed in the default dynamic library search path, you can configure specific paths for guile-ffi-cblas with the environment variable GUILE_FFI_CBLAS_LIBPATH. There are other variables that control where dynamic-link searches for libraries (LTDL_LIBRARY_PATH, LD_LIBRARY_PATH) and you may prefer to set those instead. See also https://notabug.org/ZelphirKaltstahl/guile-ml#using-guile-ffi-cblas for notes on using guile-ffi-cblas on Guix³.

Running the tests

The tests use SRFI-64.

$GUILE -L mod -s test/test-ffi-cblas.scm

Depending on your installation (see above) you might need

GUILE_FFI_CBLAS_LIBNAME=libotherblas \
GUILE_FFI_CBLAS_LIBPATH=/custom/path/lib \
$GUILE ... etc.

Coverage

CBLAS level 1

• srotg drotg crotg zrotg ⁴
• sscal dscal cscal zscal csscal zdscal
• sswap dswap cswap zswap
• scopy dcopy ccopy zcopy
• saxpy daxpy caxpy zaxpy
• sdot ddot cdotu zdotu cdotc zdotc
• snrm2 dnrm2 scnrm2 dznrm2
• sasum dasum scasum dzasum
• isamax idamax icamax izamax

CBLAS level 2

• sgemv dgemv cgemv zgemv
• sger dger cgeru zgeru cgerc zgerc

CBLAS level 3

• sgemm dgemm cgemm zgemm

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¹ See http://www.netlib.org/blas/ or https://en.wikipedia.org/wiki/Basic_Linear_Algebra_Subprograms. ↩

² Unfortunately this triggers a bug in the current version. ↩

³ A previous version of this library also included BLIS bindings, but now I have moved those to a separate library (guile-ffi-blis). ↩ .

⁴ Some distributions of libcblas do not provide these. guile-ffi-cblas will still work, just without these bindings.