/*

Test with something like:

gcc-4.9.0 -std=c11 -O3 test.c -S -o test_u.s
sed 's/movdqu/movdqa/' test_u.s > test_a.s
gcc-4.9.0 test_u.s -o test_u
gcc-4.9.0 test_a.s -o test_a

perf stat -r4 ./test_u

       1013.003257 task-clock                #    0.997 CPUs utilized            ( +-  0.01% )
     2,188,597,489 cycles                    #    2.161 GHz                      ( +-  0.01% )

perf stat -r4 ./test_a

        513.658041 task-clock                #    0.997 CPUs utilized            ( +-  0.05% )
     1,109,852,134 cycles                    #    2.161 GHz                      ( +-  0.05% )

(on a Pentium Dual-Core T3400)

*/

#define _GNU_SOURCE

#include <stdint.h>
#include <stdlib.h>
#include <memory.h>
#include <stdio.h>
#include <xmmintrin.h>

static uint32_t __attribute__((noinline)) f(__m128i *p, size_t sz)
{
    __m128i t = _mm_setzero_si128();

#define UNROLL 4
    for (size_t i = 0; i < sz/16/UNROLL; ++i)
        for (size_t j = 0; j < UNROLL; ++j)
            t = _mm_add_epi32(t, _mm_loadu_si128(p++));

    uint32_t temp[4];
    _mm_storeu_si128((__m128i *)temp, t);
    return temp[0] + temp[1] + temp[2] + temp[3];
}

int main()
{
    void *p;
    size_t sz = 1024*16;
    if (posix_memalign(&p, 4096, sz))
        abort();
    memset(p, 0, sz);
    uint32_t n = 0;
    for (int i = 0; i < 1024*1024; ++i)
        n += f(p, sz);
    printf("%d\n", n);
}