Using BLAS API in C - 5.2 English - 57404

Following is the C version of the Fortran code in section Using BLAS API in Fortran. It uses the standard BLAS API. The following process takes place during the execution of the code:

1. The matrices are transposed to account for the row-major storage of C and the column-major convention of BLAS (inherited from Fortran).

2. The function arguments are passed by address again to be in line with Fortran conventions.

3. There is a trailing underscore in the function name (dgemm_) as most Fortran compilers add this trailing underscore by default to symbol names.

4. blis.h is included as a header. A sample command to compile it and link with the AOCL-BLAS library is also shown in the following code:

   // File: BLAS_DGEMM_usage.c
   // Example code to demonstrate BLAS DGEMM usage
   
   #include <stdio.h>
   #include "blis.h"
   
   #define DIM 2
   
   int main() {
   
      double a[DIM * DIM] = { 1.0, 2.0, 3.0, 4.0 };
      double b[DIM * DIM] = { 5.0, 7.0, 6.0, 8.0 };
      double c[DIM * DIM];
      int I, J, M, N, K, lda, ldb, ldc; double alpha, beta;
   
      M = DIM;
      N = M; K = M;
      lda = M; ldb = K; ldc = M;
      alpha = 1.0;
      beta = 0.0;
   
      printf("a = \\n");
      for ( I = 0; I < M; I ++ ) {
        for ( J = 0; J < K; J ++ ) {
          printf("%f\t", a[J * K + I]);
        }
        printf("\n");
      }
   
      printf("b = \\n");
      for ( I = 0; I < K; I ++ ) {
        for ( J = 0; J < N; J ++ ) {
          printf("%f\t", b[J * N + I]);
        }
        printf("\n");
      }
   
      dgemm_("N","N",&M,&N,&K,&alpha,a,&lda,b,&ldb,&beta,c,&ldc);
      printf("c = \\n");
   
      for ( I = 0; I < M; I ++ ) {
        for ( J = 0; J < N; J ++ ) {
          printf("%f\t", c[J * N + I]);
        }
        printf("\n");
      }
   
      return 0;
   }
   

A sample compilation command with a GCC compiler for the code above:

$ gcc BLAS_DGEMM_usage.c -I/path/to/include/aocl-blas/ \
  /path/to/libblis.a -lpthread -lm