starpu-max/doc/chapters/vector_scal_cpu.texi

@c -*-texinfo-*-

@c This file is part of the StarPU Handbook.
@c Copyright (C) 2009-2011  Université de Bordeaux 1
@c Copyright (C) 2010, 2011, 2012  Centre National de la Recherche Scientifique
@c See the file starpu.texi for copying conditions.

@smallexample
#include <starpu.h>
#include <xmmintrin.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->handles array: for instance
     * task->handles[0] 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 *). 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.
     */
    struct starpu_vector_interface *vector = buffers[0];

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

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

void scal_sse_func(void *buffers[], void *cl_arg)
@{
    float *vector = (float *) STARPU_VECTOR_GET_PTR(buffers[0]);
    unsigned int n = STARPU_VECTOR_GET_NX(buffers[0]);
    unsigned int n_iterations = n/4;

    __m128 *VECTOR = (__m128*) vector;
    __m128 FACTOR __attribute__((aligned(16)));
    float factor = *(float *) cl_arg;
    FACTOR = _mm_set1_ps(factor);

    unsigned int i;	
    for (i = 0; i < n_iterations; i++)
        VECTOR[i] = _mm_mul_ps(FACTOR, VECTOR[i]);

    unsigned int remainder = n%4;
    if (remainder != 0)
    @{
        unsigned int start = 4 * n_iterations;
        for (i = start; i < start+remainder; ++i)
        @{
            vector[i] = factor * vector[i];
        @}
    @}
@}
@end smallexample