Compression mask using embedded AVX

Question

I would like to combine two 256-bit vectors ( __m256d) that contain masks as a result of a comparison operation (for example _mm256_cmp_pd) with one 256-bit vector, omitting the upper half of each Bit 64 bits.

So, if in the following, there a_i, b_i, ...are 32-bit words, and I have two 256-bit (4 x double) vectors that have the following structure:

a_0, a_0, b_0, b_0, c_0, c_0, d_0, d_0and a_1, a_1, b_1, b_1, c_1, c_1, d_1, d_1.

I would like to have one 256-bit vector with the following structure:

a_0, b_0, c_0, d_0, a_1, b_1, c_1, d_1.

How can I do this efficiently using Intel's built-in features? An affordable set of instructions is all up to AVX.

Answer 1

, , - 1s NaN , , - 0s 0.0 . , , :

 __m256 v = _mm256_set_m128(_mm256_cvtpd_ps(v0), _mm256_cvtpd_ps(v1));

, _mm256_set_m128, :

#define _mm256_set_m128(va, vb) \
        _mm256_insertf128_ps(_mm256_castps128_ps256(vb), va, 1)

:

#include <stdio.h>
#include <immintrin.h>

#define _mm256_set_m128(va, vb) \
        _mm256_insertf128_ps(_mm256_castps128_ps256(vb), va, 1)

static void printvd(const char * label, __m256d v)
{
    int64_t a[4];
    _mm256_storeu_pd((double *)a, v);
    printf("%s = %lld %lld %lld %lld\n", label, a[0],  a[1],  a[2],  a[3]);
}

static void printvf(const char * label, __m256 v)
{
    int32_t a[8];
    _mm256_storeu_ps((float *)a, v);
    printf("%s = %d %d %d %d %d %d %d %d\n", label, a[0],  a[1],  a[2],  a[3],  a[4],  a[5],  a[6],  a[7]);
}

int main()
{
    __m256d v0 = _mm256_set_pd(0.0, 1.0, 2.0, 3.0);
    __m256d v1 = _mm256_set_pd(3.0, 2.0, 1.0, 0.0);
    __m256d vcmp0 = _mm256_cmp_pd(v0, v1, 1);
    __m256d vcmp1 = _mm256_cmp_pd(v1, v0, 1);
    __m256 vcmp = _mm256_set_m128(_mm256_cvtpd_ps(vcmp0), _mm256_cvtpd_ps(vcmp1));
    printvd("vcmp0", vcmp0);
    printvd("vcmp1", vcmp1);
    printvf("vcmp ", vcmp);
    return 0;
}

:

$ gcc -Wall -mavx so_avx_test.c && ./a.out
vcmp0 = 0 0 -1 -1
vcmp1 = -1 -1 0 0
vcmp  = -1 -1 0 0 0 0 -1 -1

Answer 2

function1() . . FFFFFFFF , . . :

v0=A0000000 FFFFFFFF B0000000 FFFFFFFF C0000000 FFFFFFFF D0000000 FFFFFFFF
v1=A0000001 FFFFFFFF B0000001 FFFFFFFF C0000001 FFFFFFFF D0000001 FFFFFFFF
vr=A0000000 B0000000 C0000000 D0000000 A0000001 B0000001 C0000001 D0000001

VS2013 cl /Ox /arch:AVX sample.c gcc 4.9.0 gcc -O3 -mavx -c sample.c.

AVX .

#include <intrin.h>
#include <stdint.h>
#include <stdio.h>

//---------------------------------------------------------------------------

static void dump (void *data)
    {
    uint32_t *d32 = data;
    int index;

    for (index = 0; index < 8; index++)
        printf ("%08X ", d32 [index]);
    printf ("\n");
    }

//---------------------------------------------------------------------------

 static __m256d function1 (__m256d v0, __m256d v1)
    {
    __m256d tmp0 = _mm256_permute2f128_pd (v0, v1, 0x20);
    __m256d tmp1 = _mm256_permute2f128_pd (v0, v1, 0x31);
    return _mm256_castps_pd (_mm256_shuffle_ps (_mm256_castpd_ps (tmp0), _mm256_castpd_ps (tmp1), 0x88));
    }

//---------------------------------------------------------------------------

int main (void)
    {
    __m256d v0, v1, vr;

    v0 = _mm256_castsi256_pd (_mm256_set_epi32 (0xffffffff, 0xd0000000, 0xffffffff, 0xc0000000, 0xffffffff, 0xb0000000, 0xffffffff, 0xa0000000));
    v1 = _mm256_castsi256_pd (_mm256_set_epi32 (0xffffffff, 0xd0000001, 0xffffffff, 0xc0000001, 0xffffffff, 0xb0000001, 0xffffffff, 0xa0000001));
    vr = function1 (v0, v1);
    printf ("v0="); dump (&v0);
    printf ("v1="); dump (&v1);
    printf ("vr="); dump (&vr);
    return 0;
    }