sse sum of unsigned long long array

Question

基于浮点向量的SSE缩减，我试图对unsigned long long的数组求和，但不幸的是没有任何成功。

uint64_t vsum_uint64 (uint64_t *a, int n)
{
    uint64_t sum;    // lets say sum fits
    __m128 vsum = _mm_set1_ps(0);
    for (int i = 0; i < n; i += 2) {    // 2 unit64 in single __m128
        __m128 v = _mm_loadl_epi64(&a[i]);
        vsum = _mm_add_epi64(vsum, v);
    }
    _mm_store_ss(&sum, vsum);
    uint64_t *p = &vsum;
    sum+=*(p+1);
    // vsum = _mm_hadd_ps(vsum, vsum);
    // vsum = _mm_hadd_ps(vsum, vsum);
    return sum;
}

这应该是正确的，但是gcc仍然不能编译它。我寻找答案，但没有找到。

这是gcc说的:

main.cpp: In function ‘uint64_t vsum_uint64(const uint64_t*, int)’:
main.cpp:73:35: error: cannot convert ‘const uint64_t* {aka const long unsigned int*}’ to ‘const __m128i* {aka const __vector(2) long long int*}’ for argument ‘1’ to ‘__m128i _mm_loadl_epi64(const __m128i*)’
main.cpp:74:31: error: cannot convert ‘__m128 {aka __vector(4) float}’ to ‘__m128i {aka __vector(2) long long int}’ for argument ‘1’ to ‘__m128i _mm_add_epi64(__m128i, __m128i)’
main.cpp:77:25: error: cannot convert ‘uint64_t* {aka long unsigned int*}’ to ‘float*’ for argument ‘1’ to ‘void _mm_store_ss(float*, __m128)’
main.cpp:78:17: error: cannot convert ‘__m128* {aka __vector(4) float*}’ to ‘uint64_t* {aka long unsigned int*}’ in initialization

你能帮我一下吗?我真的很感激。

谢谢

Answer 1

以下是一些事情:

1. 用__m128i代替__m128

2. 您可以使用__m128i vsum = _mm_setzero_si128()零初始化vsum;

3. 用于数据加载，强制转换为适当的__m128i类型并使用打包加载版本(_mm_loadl_epi64只加载一个64位整数)。所以,要么

   for (int i = 0; i < n; i += 2) {    // 2 uint64 in single __m128i
       __m128i v = _mm_loadu_si128(reinterpret_cast<__m128i*>(&a[i]));
   

   或

   __m128i* pa = reinterpret_cast<__m128i*>(a);
   for (int i = 0; i < n; i += 2) {    // 2 uint64 in single __m128i
       __m128i v = _mm_loadu_si128(pa);
       pa++;
   

4. 最后你可以使用sum = vsum.m128i_u64[0] + vsum.m128i_u64[1];分配给sum，如果有一个定义的联合(有在windows/Visual-Studio，但你使用不同的环境)。