2018年12月13日 · I really can't get what "keyword" like __m128d is in C++. I'm using MSVC, and it says: The __m128d data type, for use with the Streaming SIMD Extensions 2 instructions intrinsics, is defined in <

2012年9月27日 · Late to this party but found that this works for me in MSVC where z is a variable of type __m128. #define _mm_extract_f32(v, i) _mm_cvtss_f32(_mm_shuffle_ps(v, v, i)) __m128 z = _mm_setr_ps(1.0, 2.0, 3.0, 4.0); float f = _mm_extract_f32(z, 2); OR even simpler __m128 z; float f = z.m128_f32[2]; // to get the 3rd float value in the vector

2013年1月16日 · If you want just the low element, float _mm_cvtss_f32(__m128) is good. If you want to combine the vector elements down to a single float after a loop that sums an array or does a dot-product, see Fastest way to do horizontal SSE vector sum (or other reduction)

Using a __m128i* to load from an array of int is safe because the __m128 types are defined to allow aliasing just like ISO C unsigned char*. (e.g. in gcc's headers, the definition includes __attribute__((may_alias)).) The reverse isn't safe (pointing an int* onto part of a __m128i object). MSVC guarantees that's safe, but GCC/clang don't.

2013年10月25日 · So far as I know, clang and recent versions of GCC support accessing __m128 fields by index. I don't know how to do this in ICC or MSVC. I don't know how to do this in ICC or MSVC. I guess _mm_extract_ps works for all 4 compilers but its …

2014年5月5日 · Type-punning with unions is preferable to pointer-casts. They're both undefined behaviour according to the standard, but the union is safe with gcc at least. The pointer-cast technique isn't safe with real compilers. (except maybe with SIMD __m128 types, which are defined with a may_alias attribute or something like that. Hopefully SunCC ...

2012年11月1日 · @hirschhornsalz yes, but 1 the & and &= are only defined for __m128i and not for __m128. 2 If I only have SSE (and not SSE2), it is not defined, but the intrinsic _mm_and_ps(__m128,__m128) still is. So IMHO, there should be operators & and &= for __m128 implemented using that intrinsic. btw, I like your handle -- will use Hirschhornsalz for ...

__m128 is allowed to alias other types, including float or __m128d. (This is why gcc defines __m128 as may_alias, so it compiles as expected even with the default strict-aliasing.) Most of the time compilers will fold load intrinsics into memory operands for ALU instructions, so your last paragraph doesn't really apply either (at least with ...

2015年11月24日 · I've got some code that works with __m128 values. I'm using x86-64 SSE intrinsics on these values and I find that if the values are unaligned in memory I get a crash. This is due to my compiler (...

2012年11月30日 · __m128 x; __m128i n = (__m128i)x; This operation copies the bit representation of x to n, and is useful for implementing various branch-free conditional operations operating on SSE floating point registers. On MSVC 11, it gives