starpu-max/doc/vector_scal_cpu.texi

/*
 * This example complements vector_scale.c: here we implement a CPU version.
 */

#include <starpu.h>

/* This kernel takes a buffer and scales it by a constant factor */
void scal_cpu_func(void *buffers[], void *cl_arg)
@{
    unsigned i;
    float *factor = cl_arg;

    /* 
     * The "buffers" array matches the task->buffers array: for instance
     * task->buffers[0].handle is a handle that corresponds to a data with
     * vector "interface", so that the first entry of the array in the
     * codelet  is a pointer to a structure describing such a vector (ie.
     * struct starpu_vector_interface_s *). Here, we therefore manipulate
     * the buffers[0] element as a vector: nx gives the number of elements
     * in the array, ptr gives the location of the array (that was possibly
     * migrated/replicated), and elemsize gives the size of each elements.
     */

    starpu_vector_interface_t *vector = buffers[0];

    /* length of the vector */
    unsigned n = STARPU_GET_VECTOR_NX(vector);

    /* get a pointer to the local copy of the vector : note that we have to
     * cast it in (float *) since a vector could contain any type of
     * elements so that the .ptr field is actually a uintptr_t */
    float *val = (float *)STARPU_GET_VECTOR_PTR(vector);

    /* scale the vector */
    for (i = 0; i < n; i++)
        val[i] *= *factor;
@}