内在的mulx指令

问题描述

根据 Intel公司的文档应该有来间接产生 mulx / code>在GCC中使用 -mbmi2 （或 -march = haswell ），但我宁愿做这更直接地使用一个内部函数。

为什么ADX内在函数存在，但对于 mulx a href =http://www.intel.com/content/www/us/en/intelligent-systems/intel-technology/ia-large-integer-arithmetic-paper.html rel =nofollow> Intel的文档

解决方案

生成64位Integer乘法的mulx指令的内在是_mulx_u64（）。下面是同样的例子：

  #include  
 int main（）
 {
 unsigned __int64 a = 0x0fffffffffffffff; 
 unsigned __int64 b = 0xf0000000; 
 unsigned __int64 c，d; 
 d = _mulx_u64（a，b，& c）; 
 printf_s（％＃I64x *％＃I64x =％＃I64x％I64x \\\
，a，b，c，d）; 
 
 
 
 
 
变量c将保存结果的高64位和变量 d将保持结果的低64位。 Microsoft Visual Studio编译器也支持此内部函数。我们正在努力更新白皮书（新指令支持大整数算术）并使用正确的内部函数。感谢您将此引入我们的注意。
 
The mulx instruction was introduced with the BMI2 instruction set starting with the Haswell processor.

According to Intel's documentation there should be an intrinsic for mulx
unsigned __int64 umul128(unsigned __int64 a, unsigned __int64 b, unsigned __int64 * hi);
However, I find no such intrinsic from Intel's intrinsic guide online under BMI2 or in general. I do however find the addcarry intrinsics from the ADX instruction set.
According to this link the intrinsic is mulx_u64 but I don't find that one either.
MSVC added a _umul128 intrinsic in MSVC 2005 but that only produces mul and not mulx (and I have no idea how to enable BMI2 in MSVC).
I can produce the mulx instruction indirectly using __int128 in GCC with -mbmi2 (or -march=haswell) but I would prefer to do this more directly using an intrinsic.
Why do the ADX intrinsics exist but not one for mulx as defined in Intel's documentation?
 解决方案 
The intrinsic which generates mulx instruction for 64 bit Integer multiplication is _mulx_u64(). Below is an example for the same:
    #include <stdio.h>
    int main()
    {
        unsigned __int64 a = 0x0fffffffffffffff;
        unsigned __int64 b = 0xf0000000;
        unsigned __int64 c, d;
        d = _mulx_u64(a, b, &c);
        printf_s("%#I64x * %#I64x = %#I64x%I64x\n", a, b, c, d);
    }
Variable "c" will hold the higher 64 bits of the result and variable "d" will hold the lower 64 bits of the result. This intrinsic is also supported in Microsoft Visual Studio Compiler. We are working on updating the white paper (New Instructions Support Large Integer Arithmetic) with the right intrinsic. Thanks for bringing this to our attention.
                        
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