从64位无符号整数初始化__m128类型

问题描述

和类似的* _epi64指令似乎使用并依赖于 __ m64 类型。我想初始化一个 __ m128 类型的变量，使它的高64位为0，低64位设置为 x ，其中 x 的类型为 uint64_t （或类似的无符号64位类型）。

The _mm_set_epi64 and similar *_epi64 instructions seem to use and depend on __m64 types. I want to initialize a variable of type __m128 such that the upper 64 bits of it are 0, and the lower 64 bits of it are set to x, where x is of type uint64_t (or similar unsigned 64-bit type). What's the "right" way of doing so?

最好是以不依赖于编译器的方式进行。

Preferably, this should be done in a compiler-independent manner.

推荐答案

回答您的问题，关于如何加载64位值到XMM寄存器的低64位，同时将高64位的 _mm_loadl_epi64 （& x） 的源代码可以回答95 ％的SSE / AVX上SO的问题。 Agner实现了这个（从文件vectori128.h）为多个编译器和64位和32位。请注意，MSVC 32位Agner的解决方案说这是低效的，但其他解决方案更糟糕。我想这是Mysticial的意思是没有一个好的方法来做。

In regards to _mm_set_epi64 I said once that looking at the source code of Agner Fog's Vector Class Library can answer 95% of the question on SSE/AVX on SO. Agner implemented this (from the file vectori128.h) for multiple compilers and for 64-bit and 32-bit. Note that the solution for MSVC 32-bit Agner says "this is inefficient, but other solutions are worse". I guess that's what Mysticial means by "There isn't a good way to do it.".

Vec2q(int64_t i0, int64_t i1) {
#if defined (_MSC_VER) && ! defined(__INTEL_COMPILER)
        // MS compiler has no _mm_set_epi64x in 32 bit mode
#if defined(__x86_64__)                                    // 64 bit mode
#if _MSC_VER < 1700
        __m128i x0 = _mm_cvtsi64_si128(i0);                // 64 bit load
        __m128i x1 = _mm_cvtsi64_si128(i1);                // 64 bit load
        xmm = _mm_unpacklo_epi64(x0,x1);                   // combine
#else
        xmm = _mm_set_epi64x(i1, i0);
#endif
#else   // MS compiler in 32-bit mode
        union {
            int64_t q[2];
            int32_t r[4];
        } u;
        u.q[0] = i0;  u.q[1] = i1;
        // this is inefficient, but other solutions are worse
        xmm = _mm_setr_epi32(u.r[0], u.r[1], u.r[2], u.r[3]);
#endif  // __x86_64__
#else   // Other compilers
        xmm = _mm_set_epi64x(i1, i0);
#endif
};

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