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Optimus1
Asked:2022-07-04 00:45:23 +0800 CST2022-07-04 00:45:23 +0800 CST

SIMD - 如何从相同类型的2个向量中添加值

  • 772

请告诉我如何从相同类型的向量中添加值，但这些值本身被这些向量中不同数量的字节占用。

这是一个例子：

int main()
{
    //--------------------------------------------------------------
    int my_int_sequence[16] = { 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 };


    __m128i my_int_sequence_m128i_1 = _mm_loadu_si128((__m128i*) & my_int_sequence[0]);
    __m128i my_int_sequence_m128i_2 = _mm_loadu_si128((__m128i*) & my_int_sequence[4]);
    __m128i my_int_sequence_m128i_3 = _mm_loadu_si128((__m128i*) & my_int_sequence[8]);
    __m128i my_int_sequence_m128i_4 = _mm_loadu_si128((__m128i*) & my_int_sequence[12]);
    //--------------------------------------------------------------



    //-----------------------------------------------------------------------
    char my_char_mask[16] = { 1,0,1,1,0,1,0,1,1,1,0,1,0,1,0,1 };

    __m128i my_char_mask_my_m128i = _mm_loadu_si128((__m128i*) &my_char_mask[0]);
    //-----------------------------------------------------------------------

}

也就是说，我在 my_int_sequence 数组中有一个 int 值数组——并且由于所有 16 个 int 值都无法放入一个 __m128i 向量中，因此我将这些值 4 个值加载到第 4 个 __m128i 向量中。

我还有一个 16 字节的数组，我也将它加载到 my_char_mask_my_m128i 向量中。

现在我想添加到 my_int_sequence_m128i_x 向量的每个 4 字节值，就好像来自 my_char_mask_my_m128i 向量的相应一字节值一样。

问题显然是我需要把不同的维度加起来。可能吗？

也许我需要向量 my_char_mask_my_m128i 的每个字节 - 如何将其转换为 4 个字节？

c++ c

1 个回答

  1. Best Answer

    我看到你已经部分回答了：这个 SIMD 指令是做什么的？.

    但我仍然建议在这里使用它_mm_cvtepi8_epi32，因为签名int和签名在这里加起来char。

    原理很简单：展开char为int，相加，掩码右移4个字节。等4次。

    #include <stdio.h>
#include <x86intrin.h>

void show_sequence(const char* pstrMsg, int* pSeq);
void show_mask(const char* pstrMsg, char* pMask);

int main()
{
    int my_int_sequence[16] = { 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 };
    char my_char_mask[16] = { 1,0,1,1,0,1,0,1,1,1,0,1,0,1,0,1 };
    
    show_sequence("Source sequence", my_int_sequence);
    show_mask(    "Characters mask", my_char_mask);
    
    __m128i my_int_sequence_m128i_1 = _mm_loadu_si128((__m128i*)&my_int_sequence[0]);
    __m128i my_int_sequence_m128i_2 = _mm_loadu_si128((__m128i*)&my_int_sequence[4]);
    __m128i my_int_sequence_m128i_3 = _mm_loadu_si128((__m128i*)&my_int_sequence[8]);
    __m128i my_int_sequence_m128i_4 = _mm_loadu_si128((__m128i*)&my_int_sequence[12]);
    
    __m128i my_char_mask_my_m128i = _mm_loadu_si128((__m128i*)my_char_mask);
    
    my_int_sequence_m128i_1 = _mm_add_epi32(my_int_sequence_m128i_1, _mm_cvtepi8_epi32(my_char_mask_my_m128i));
    
    my_char_mask_my_m128i = _mm_bsrli_si128(my_char_mask_my_m128i, 4);
    my_int_sequence_m128i_2 = _mm_add_epi32(my_int_sequence_m128i_2, _mm_cvtepi8_epi32(my_char_mask_my_m128i));
    
    my_char_mask_my_m128i = _mm_bsrli_si128(my_char_mask_my_m128i, 4);
    my_int_sequence_m128i_3 = _mm_add_epi32(my_int_sequence_m128i_3, _mm_cvtepi8_epi32(my_char_mask_my_m128i));
    
    my_char_mask_my_m128i = _mm_bsrli_si128(my_char_mask_my_m128i, 4);
    my_int_sequence_m128i_4 = _mm_add_epi32(my_int_sequence_m128i_4, _mm_cvtepi8_epi32(my_char_mask_my_m128i));
    
    _mm_store_si128((__m128i*)&my_int_sequence[0], my_int_sequence_m128i_1);
    _mm_store_si128((__m128i*)&my_int_sequence[4], my_int_sequence_m128i_2);
    _mm_store_si128((__m128i*)&my_int_sequence[8], my_int_sequence_m128i_3);
    _mm_store_si128((__m128i*)&my_int_sequence[12], my_int_sequence_m128i_4);
    
    show_sequence("Result sequence", my_int_sequence);
    return 0;
}


void show_sequence(const char* pstrMsg, int* pSeq)
{
    printf("%s: {", pstrMsg);
    for (char i=0; i<15; ++i)
        printf("%2d, ", pSeq[i]);
    printf("%2d}\n", pSeq[15]);
}

void show_mask(const char* pstrMsg, char* pMask)
{
    printf("%s: {", pstrMsg);
    for (char i=0; i<15; ++i)
        printf("%2d, ", (int)pMask[i]);
    printf("%2d}\n", (int)pMask[15]);
}

    Source sequence: { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15}
Characters mask: { 1,  0,  1,  1,  0,  1,  0,  1,  1,  1,  0,  1,  0,  1,  0,  1}
Result sequence: { 1,  1,  3,  4,  4,  6,  6,  8,  9, 10, 10, 12, 12, 14, 14, 16}
    • 6

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