intrinsics

问题 According to this question I implemented the horizontal addition this time 5 by 5 and 7 by 7. It does the job correctly but it is not fast enough. Can it be faster than what it is? I tried to use hadd and other instruction but the improvement is restricted. For examlple, when I use _mm256_bsrli_epi128 it is slightly better but it needs some extra permutation that ruins the benefit because of the lanes. So the question is how it should be implemented to gain more performance. The same story is

问题 I was reading this on MSDN, and it says You should not access the __m128i fields directly. You can, however, see these types in the debugger. A variable of type __m128i maps to the XMM[0-7] registers. However, it doesn't explain why. Why is it? For example, is the following "bad": void func(unsigned short x, unsigned short y) { __m128i a; a.m128i_i64[0] = x; __m128i b; b.m128i_i64[0] = y; // Now do something with a and b ... } Instead of doing the assignments like in the example above, should

问题 Gprof tells me that my computationally heavy program spends most of it's time (36%) hashing using AP-Hash. I can't reduce the call count but I would still like to make it faster, can I call intrinsic SHA from a c program? Do I need the intel compiler or can I stick with gcc? 回答1: SHA instructions are now available in Goldmont architecture. It was released around September, 2016. According to the Intel Intrinsics Guide, these are the intrinsics of interest: __m128i _mm_sha1msg1_epu32 (__m128i

问题 This is a followup on this question. The code below for a 4x4 matrix multiplication C = AB compiles fine on ICC on all optimization settings. It executes correctly on -O1 and -O2, but gives an incorrect result on -O3. The problem seems to come from the _mm256_storeu_pd operation, as substituting it (and only it) with the asm statement below gives correct results after execution. Any ideas? inline void RunIntrinsics_FMA_UnalignedCopy_MultiplyMatrixByMatrix(double *A, double *B, double *C) {

问题 This is a followup on this question. The code below for a 4x4 matrix multiplication C = AB compiles fine on ICC on all optimization settings. It executes correctly on -O1 and -O2, but gives an incorrect result on -O3. The problem seems to come from the _mm256_storeu_pd operation, as substituting it (and only it) with the asm statement below gives correct results after execution. Any ideas? inline void RunIntrinsics_FMA_UnalignedCopy_MultiplyMatrixByMatrix(double *A, double *B, double *C) {

问题 I'm writing a program using Intel intrinsics. I want to use _mm_permute_pd intrinsic, which is only available on CPUs with AVX. For CPUs without AVX I can use _mm_shuffle_pd but according to the specs it is much slower than _mm_permute_pd . Do the header files for Intel intrinsics define constants that allow me to distinguish whether AVX is supported so that I can write sth like this: #ifdef __IS_AVX_SUPPORTED__ // is there sth like this defined? // use _mm_permute_pd # else // use _mm

问题 I am new to SSE programming so I am hoping someone out there can help me. I recently implemented a function using GCC SSE intrinsics to compute the sum of an array of 32-bit integers. The code for my implementation is given below. int ssum(const int *d, unsigned int len) { static const unsigned int BLOCKSIZE=4; unsigned int i,remainder; int output; __m128i xmm0, accumulator; __m128i* src; remainder = len%BLOCKSIZE; src = (__m128i*)d; accumulator = _mm_loadu_si128(src); output = 0; for(i

问题 I would like to copy a relatively short sequence of memory (less than 1 KB, typically 2-200 bytes) in a time critical function. The best code for this on CPU side seems to be rep movsd . However I somehow cannot make my compiler to generate this code. I hoped (and I vaguely remember seeing so) using memcpy would do this using compiler built-in intrinsics, but based on disassembly and debugging it seems compiler is using call to memcpy/memmove library implementation instead. I also hoped the

问题 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? Preferably, this should be done in a compiler-independent manner. 回答1: To answser your question about how to load a 64-bit value into the lower 64-bits of a XMM register while

问题 I was reading about __noop and the MSDN example is #if DEBUG #define PRINT printf_s #else #define PRINT __noop #endif int main() { PRINT("\nhello\n"); } and I don't see the gain over just having an empty macro: #define PRINT The generated code is the same. What's a valid example of using __noop that actually makes it useful? 回答1: The __noop intrinsic specifies that a function should be ignored and the argument list be parsed but no code be generated for the arguments. It is intended for use