intrinsics

问题 Seemed to have fixed it myself by type casting the cij2 pointer inside the mm256 call so _mm256_storeu_pd((double *)cij2,vecC); I have no idea why this changed anything... I'm writing some code and trying to take advantage of the Intel manual vectorization. But whenever I run the code I get a segmentation fault on trying to use my double *cij2. if( q == 0) { __m256d vecA; __m256d vecB; __m256d vecC; for (int i = 0; i < M; ++i) for (int j = 0; j < N; ++j) { double cij = C[i+j*lda]; double

问题 There are two ways of implementation of accumulation in sse intrinsic. But one of them gets the wrong result. #include <smmintrin.h> int main(int argc, const char * argv[]) { int32_t A[4] = {10, 20, 30, 40}; int32_t B[8] = {-1, 2, -3, -4, -5, -6, -7, -8}; int32_t C[4] = {0, 0, 0, 0}; int32_t D[4] = {0, 0, 0, 0}; __m128i lv = _mm_load_si128((__m128i *)A); __m128i rv = _mm_load_si128((__m128i *)B); // way 1 unexpected rv += lv; _mm_store_si128((__m128i *)C, rv); // way 2 expected rv = _mm_load

问题 There are two ways of implementation of accumulation in sse intrinsic. But one of them gets the wrong result. #include <smmintrin.h> int main(int argc, const char * argv[]) { int32_t A[4] = {10, 20, 30, 40}; int32_t B[8] = {-1, 2, -3, -4, -5, -6, -7, -8}; int32_t C[4] = {0, 0, 0, 0}; int32_t D[4] = {0, 0, 0, 0}; __m128i lv = _mm_load_si128((__m128i *)A); __m128i rv = _mm_load_si128((__m128i *)B); // way 1 unexpected rv += lv; _mm_store_si128((__m128i *)C, rv); // way 2 expected rv = _mm_load

问题 The answer What are _mm_prefetch() locality hints? goes into details on what the hint means. My question is: which one do I WANT ? I work on a function that is called repeatedly, billions of times, with some int parameter among others. First thing I do is to look up some cached value using that parameter (its low 32 bits) as a key into 4GB cache. Based on the algorithm from where this function is called, I know that most often that key will be doubled (shifted left by 1 bit) from one call to

问题 The answer What are _mm_prefetch() locality hints? goes into details on what the hint means. My question is: which one do I WANT ? I work on a function that is called repeatedly, billions of times, with some int parameter among others. First thing I do is to look up some cached value using that parameter (its low 32 bits) as a key into 4GB cache. Based on the algorithm from where this function is called, I know that most often that key will be doubled (shifted left by 1 bit) from one call to

问题 The answer What are _mm_prefetch() locality hints? goes into details on what the hint means. My question is: which one do I WANT ? I work on a function that is called repeatedly, billions of times, with some int parameter among others. First thing I do is to look up some cached value using that parameter (its low 32 bits) as a key into 4GB cache. Based on the algorithm from where this function is called, I know that most often that key will be doubled (shifted left by 1 bit) from one call to

问题 The answer What are _mm_prefetch() locality hints? goes into details on what the hint means. My question is: which one do I WANT ? I work on a function that is called repeatedly, billions of times, with some int parameter among others. First thing I do is to look up some cached value using that parameter (its low 32 bits) as a key into 4GB cache. Based on the algorithm from where this function is called, I know that most often that key will be doubled (shifted left by 1 bit) from one call to

问题 I have a bunch of packed floats inside an XMM register (using SSE intrinsics): __m128 xmm = _mm_set_ps(4.0f, 3.0f, 2.0f, 1.0f); I'd like to convert all of these to integers in one go. I found an intrinsic, that does what I want ( _mm_cvtps_pi16() ), but it yields 4x16-bit short instead of full-blown int . An intrinsic called _mm_cvtps_pi32() yields int , but only for the two lower values in xmm . I can use it, extract the values, move things around and use it again, but is there a simpler way

问题 I am trying to do left rotation of a 128 bit number in AVX2. Since there is no direct method of doing this, I have tried using left shift and right shift to accomplish my task. Here is a snippet of my code to do the same. l = 4; r = 4; targetrotate = _mm_set_epi64x (l, r); targetleftrotate = _mm_sllv_epi64 (target, targetrotate); The above c ode snippet rotates target by 4 to the left. When I tested the above code with a sample input, I could see the result is not rotated correctly. Here is

问题 I am trying to do left rotation of a 128 bit number in AVX2. Since there is no direct method of doing this, I have tried using left shift and right shift to accomplish my task. Here is a snippet of my code to do the same. l = 4; r = 4; targetrotate = _mm_set_epi64x (l, r); targetleftrotate = _mm_sllv_epi64 (target, targetrotate); The above c ode snippet rotates target by 4 to the left. When I tested the above code with a sample input, I could see the result is not rotated correctly. Here is