Developer Reference for Intel® oneAPI Math Kernel Library - C

Developer Reference

  • 2021.1
  • 12/04/2020
  • Public Content
Contents

C Interface Conventions for BLAS Routines

CBLAS, the C interface to the Basic Linear Algebra Subprograms (BLAS), provides a C language interface to BLAS routines for
Intel® oneAPI Math Kernel Library
. While you can call the Fortran implementation of BLAS, for coding in C the CBLAS interface has some advantages such as allowing you to specify column-major or row-major ordering with the
layout
 parameter.
For more information about calling Fortran routines from C in general, and specifically about calling BLAS and CBLAS routines, see " Mixed-language Programming with the
Intel® oneAPI
 Math Kernel Library
" in the
Intel® oneAPI
 Math Kernel Library
 Developer Guide
.
This reference contains syntax in C for both the CBLAS interface and the Fortran BLAS routines.
In CBLAS, the Fortran routine names are prefixed with
cblas_
 (for example,
dasum
 becomes
cblas_dasum
). Names of all CBLAS functions are in lowercase letters.
Complex functions
?dotc
 and
?dotu
 become CBLAS subroutines (void functions); they return the complex result via a void pointer, added as the last parameter. CBLAS names of these functions are suffixed with
_sub
. For example, the BLAS function
cdotc
 corresponds to
cblas_cdotc_sub
.
Users of the CBLAS interface should be aware that the CBLAS are just a C interface to the BLAS, which is based on the FORTRAN standard and subject to the FORTRAN standard restrictions. In particular, the output parameters should not be referenced through more than one argument.
This interface is not implemented in the Sparse BLAS Level 2 and Level 3 routines.
The arguments of CBLAS functions comply with the following rules:
  • Input arguments are declared with the
    const
     modifier.
  • Non-complex scalar input arguments are passed by value.
  • Complex scalar input arguments are passed as void pointers.
  • Array arguments are passed by address.
  • BLAS character arguments are replaced by the appropriate enumerated type.
  • Level 2 and Level 3 routines acquire an additional parameter of type
    CBLAS_LAYOUT
     as their first argument. This parameter specifies whether two-dimensional arrays are row-major (
    CblasRowMajor
    ) or column-major (
    CblasColMajor
    ).

Enumerated Types

The CBLAS interface uses the following enumerated types: 
enum CBLAS_LAYOUT {
   CblasRowMajor=101,  /* row-major arrays */
   CblasColMajor=102};   /* column-major arrays */
enum CBLAS_TRANSPOSE {
   CblasNoTrans=111,     /* trans='N' */
   CblasTrans=112,       /* trans='T' */
   CblasConjTrans=113};  /* trans='C' */
enum CBLAS_UPLO {
   CblasUpper=121,        /* uplo ='U' */
   CblasLower=122};       /* uplo ='L' */
enum CBLAS_DIAG {
   CblasNonUnit=131,      /* diag ='N' */
   CblasUnit=132};        /* diag ='U' */
enum CBLAS_SIDE {
   CblasLeft=141,         /* side ='L' */
   CblasRight=142};       /* side ='R' */

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.