错误:在C中强制转换用户定义的数据类型 [英] Error : casting user defined data types in c

问题描述

这是我的问题的更简单视图，我想将浮点值转换为已定义的类型v4si(我想使用SIMD操作进行优化.)请帮助将浮点/双精度值转换为已定义的类型.

This is a simpler view of my Problem, I want to convert a float value into defined type v4si (I want to use SIMD Operation for optimization.) Please help to convert float/double value to a defined type.

#include<stdio.h>

typedef double v4si __attribute__ ((vector_size (16)));

int main()
{
    double stoptime=36000;
    float x =0.5*stoptime;
    float * temp = &x;
    v4si a = ((v4si)x);   // Error: Incompatible data types
    v4si b;
    v4si *c;
    c = ((v4si*)&temp);   // Copies address of temp,           
    b = *(c);                   
    printf("%f\n" , b);      //    but printing (*c) crashes program
}

推荐答案

您似乎正在使用

You appear to be using GCC vector extensions. The following code shows how to do broadcasts, vector + scalar, vector*scalar, loads and stores using vector extensions. #include

#if defined(__clang__)
typedef float v4sf __attribute__((ext_vector_type(4)));
#else
typedef float v4sf __attribute__ ((vector_size (16)));
#endif

void print_v4sf(v4sf a) { for(int i=0; i<4; i++) printf("%f ", a[i]); puts(""); }

int main(void) {
  v4sf a;
  //broadcast a scalar
  a = ((v4sf){} + 1)*3.14159f;  
  print_v4sf(a);

  // vector + scalar
  a += 3.14159f;
  print_v4sf(a);

  // vector*scalar
  a *= 3.14159f;
  print_v4sf(a);

  //load from array
  float data[] = {1, 2, 3, 4};
  a = *(v4sf*)data;
  //a = __builtin_ia32_loadups(data);

  //store to array
  float store[4];
  *(v4sf*)store = a;
  for(int i=0; i<4; i++) printf("%f ", store[i]); puts("");
}

Clang 4.0 和 ICC 17 支持GCC矢量扩展的子集.但是，它们都不支持GCC支持的vector + scalar或vector*scalar操作. Clang的一种解决方法是使用Clang的OpenCL矢量扩展名.我不了解ICC的解决方法. MSVC不支持我所知道的任何一种矢量扩展.

Clang 4.0 and ICC 17 support a subset of the GCC vector extensions. However, neither of them support vector + scalar or vector*scalar operations which GCC supports. A work around for Clang is to use Clang's OpenCL vector extensions. I don't know of a work around for ICC. MSVC does not support any kind of vector extension that I am aware of.

即使使用GCC支持vector + scalar和vector*scalar，您也不能执行vector = scalar(但可以使用Clang的OpenCL矢量扩展名).相反，您可以使用此技巧.

With GCC even though it supports vector + scalar and vector*scalar you cannot do vector = scalar (but you can with Clang's OpenCL vector extensions). Instead you can use this trick.

a = ((v4sf){} + 1)*3.14159f;

我会按照Paul R的建议做，并使用与四大主要C/C ++编译器(GCC，Clang，ICC和MSVC)兼容的内在函数.

I would do as Paul R suggests and use intrinsics which are mostly compatible with the four major C/C++ compilers: GCC, Clang, ICC, and MSVC.

这是每个使用GCC的矢量扩展名和Clang的OpenCL矢量扩展名的编译器支持的表.

Here is a table of what is supported by each compiler using GCC's vector extensions and Clang's OpenCL vector extensions.

                                gcc  g++  clang  icc   OpenCL
unary operations                
[]                              yes  yes  yes    yes   yes
+, –                            yes  yes  yes    yes   yes
++, --                          yes  yes  no     no    no
~                               yes  yes  yes    yes   yes
!                               no   yes  no     no    yes 

binary vector op vector         
+,–,*,/,%                       yes  yes  yes    yes   yes    
&,|,^                           yes  yes  yes    yes   yes
>>,<<                           yes  yes  yes    yes   yes
==, !=, >, <, >=, <=            yes  yes  yes    yes   yes
&&, ||                          no   yes  no     no    yes

binary vector op scalar         
+,–,*,/,%                       yes  yes  no     no    yes
&,|,^                           yes  yes  no     no    yes
>>,<<                           yes  yes  no     no    yes
==, !=, >, <, >=, <=            yes  yes  no     no    yes                      
&&, ||                          no   yes  no     no    yes

assignment
vector = vector                 yes  yes  yes    yes   yes
vector = scalar                 no   no   no     no    yes                                              

ternary operator
?:                              no   yes  no     no    ?

我们看到Clang和ICC不支持GCC的vector operator scalar操作. C ++模式下的GCC支持除vector = scalar之外的所有内容. Clang的OpenCL矢量扩展支持除三元运算符以外的所有内容. Clang的文档声称可以，但是我无法正常工作. C模式下的GCC附加不支持二进制逻辑运算符或三元运算符.

We see that Clang and ICC do not support GCC's vector operator scalar operations. GCC in C++ mode supports everything but vector = scalar. Clang's OpenCL vector extensions support everything except maybe the ternary operator. Clang's documentation claims it does but I don't get it to work. GCC in C mode additional does not support binary logical operators or the ternary operator.

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