vector.c

/*
Increase the chance that the compiler will use SIMD instructions.

Basically a more abstract and ISA portable (TODO?) version of intrinsics.

Note however that the GCC and other compiles have an auto-vectorization
optimization, which might use SIMD even if you don't use the vector extensions.

TODO: is explicit alignment attribute necessary, or automatically done?
*/

#include "common.h"

typedef int int4 __attribute__ ((vector_size(4 * sizeof(int))));

/*
TODO: SIMD to scalar operations don't appear possible without intrinsics:
http://stackoverflow.com/questions/31597302/gcc-c-vector-extension-how-to-check-if-result-of-any-element-wise-comparison-is
*/
int int4_eq(int4 i, int4 j) {
    return
        i[0] == j[0] &&
        i[1] == j[1] &&
        i[2] == j[2] &&
        i[3] == j[3]
    ;
}

int main(void) {
    /* Hello world. */
    {
        int4 i = {1, 2, 3, 4};
        int4 j = {5, 6, 7, 8};
        int4 k = i + j;
        assert(int4_eq(k, (int4){6, 8, 10, 12}));
    }

    /* From / to array. TODO any better way than going over all indices?
     * Intrinsic way: _mm_load_pd family.
     * */
    {
        int is[] = {1, 2, 3, 4};
        int js[] = {5, 6, 7, 8};
        int ks[4];
        int ks2[] = {6, 8, 10, 12};
        int4 i;
        int4 j;
        int4 k;
        i[0] = is[0];
        i[1] = is[1];
        i[2] = is[2];
        i[3] = is[3];
        j[0] = js[0];
        j[1] = js[1];
        j[2] = js[2];
        j[3] = js[3];
        k = i + j;
        ks[0] = k[0];
        ks[1] = k[1];
        ks[2] = k[2];
        ks[3] = k[3];
        assert(memcmp(ks, ks2, sizeof(ks)) == 0);
    }

    return EXIT_SUCCESS;
}