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How to convert 'long long' (or __int64) to __m64

What is the correct way to convert __int64 to __m64 for use with SSE?

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With gcc, you can just use _mm_set_pi64x :

 #include <mmintrin.h> __int64 i = 0x123456LL; __m64 v = _mm_set_pi64x(i);

Note that not all compilers have _mm_set_pi64x defined in mmintrin.h . For gcc, it is defined as follows:

 extern __inline __m64 __attribute__((__gnu_inline__, __always_inline__, __artificial__)) _mm_set_pi64x (long long __i) { return (__m64) __i; }

which suggests that you might just use a listing if you want, for example.

 __int64 i = 0x123456LL; __m64 v = (__m64)i;

Otherwise, if you are stuck with an overly attractive compiler like Visual C / C ++, as a last resort, you can simply use the union and implement your own own:

 #ifdef _MSC_VER // if Visual C/C++ __inline __m64 _mm_set_pi64x (const __int64 i) { union { __int64 i; __m64 v; } u; ui = i; return uv; } #endif

Please note: strictly speaking, this is UB, since we are writing one version of the union and reading from another, but it should work in this case.

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Source: https://habr.com/ru/post/907209/

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