guile-ffi-cblas

guile-ffi-cblas

This is a set of Guile FFI bindings for two libraries of linear algebra subprograms, CBLAS and BLIS. They provide operations such as vector dot product, matrix-vector product, matrix-matrix product, and so on.

The bindings for either library are entirely independent. You do not need to have BLIS installed to use the CBLAS bindings or viceversa. I am packaging them together because they happen to share some code.

CBLAS (or BLAS) is by far the more popular library, and it probably has the fastest implementation on your system. However BLIS is much more regular and nicer to program for. These bindings are for the BLIS' ‘typed’ API (https://github.com/flame/blis/blob/master/docs/BLISTypedAPI.md).

Both sets of bindings work in the same way. Upon importing (ffi cblas) (or (ffi blis)), the bindings will attempt to load CBLAS (or BLIS) dynamically from the default dynamic library path. If your CBLAS (or BLIS) is somewhere else, you can specify a path with the environment variable GUILE_FFI_CBLAS_LIBPATH (or GUILE_FFI_BLIS_LIBPATH). You can configure the name of the library itself with GUILE_FFI_CBLAS_LIBNAME (or GUILE_FFI_BLIS_LIBNAME). The default name is libcblas (or libblis). For example, on my system, the CBLAS library is actually called libtatlas.

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. BLIS doesn't have this problem.

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

The bindings also provide type generic versions of the functions (e.g. dotv for BLIS sdotv ddotv cdotv zdotv). These simply call one of the typed variants according to the type of the first array argument.

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

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. BLIS doesn't mess up negative strides, so it avoids this problem.

Running the tests

The tests use SRFI-64.

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

---

BLIS level 1

• sdaxpy ddaxpy cdaxpy zdaxpy
• sdaxpby ddaxpby cdaxpby zdaxpby
• sdotv ddotv cdotv zdotv

BLIS level 2

• sgemv dgemv cgemv zgemv
• sger dger cger zger

BLIS level 3

• sgemm dgemm cgemm zgemm