avx2

问题 This question already has answers here : Load address calculation when using AVX2 gather instructions (3 answers) Closed last year . Intel's Intrinsic Guide says: __m128i _mm_i32gather_epi32 (int const* base_addr, __m128i vindex, const int scale) And: Description Gather 32-bit integers from memory using 32-bit indices. 32-bit elements are loaded from addresses starting at base_addr and offset by each 32-bit element in vindex (each index is scaled by the factor in scale). Gathered elements are

问题 I am trying to familiarize myself with the 256-bit AVX instructions available on some of the newer Intel processors. I have already verified that my i7-4720HQ supports 256-bit AVX instructions. The problem I am having is that the VMOVAPS instruction, which should copy 8 single precision floating point values, is only copying 4. dot PROC VMOVAPS YMM1, ymmword ptr [RCX] VDPPS YMM2, YMM1, ymmword ptr [RDX], 255 VMOVAPS ymmword ptr [RCX], YMM2 MOVSS XMM0, DWORD PTR [RCX] RET dot ENDP In case you

问题 I want to vectorize a[i] = a[i-1] +c by AVX2 instructions. It seems its un vectorizable because of the dependencies. I've vectorized and want to share the answer here to see if there is any better answer to this question or my solution is good. 回答1: I have implemented the following function for vectorizing this and it seems OK! The speedup is 2.5x over gcc -O3 Here is the solution: // vectorized inline void vec(int a[LEN], int b, int c) { // b=1 and c=2 in this case int i = 0; a[i++] = b;//0

问题 I have vectorized the the inner loop of matrix addition using intrinsics instruction of AVX2, I also have the latency table from here. I expect that speedup should be a factor of 5, because almost 4 latency happens in 1024 iterations over 6 latency in 128 iterations, but the speedup is a factor of 3. so the question is what else is here that I don't see. I'm using gcc, coding in c, intrinsics, CPU is skylake 6700hq Here is c and assembly out put of the inner loop. global data: int __attribute

问题 I have a use case, where I have array of bits each bit is represented as 8 bit integer for example uint8_t data[] = {0,1,0,1,0,1,0,1}; I want to create a single integer by extracting only lsb of each value. I know that using int _mm_movemask_pi8 (__m64 a) function I can create a mask but this intrinsic only takes a msb of a byte not lsb. Is there a similar intrinsic or efficient method to extract lsb to create single 8 bit integer? 回答1: There is no direct way to do it, but obviously you can

问题 Is it required to save/push the any XMM registers to the stack before the assembly function call? Because am observing the crash issue in my code with release mode for 64-bit development(Using AVX2). In debug mode its working fine. I tried with saving the content of the XMM8 register and restoring it at end of function call then its working fine. Any idea or references? 回答1: Yes, on Microsoft Windows you are required to preserve the XMM6-XMM15 registers. See http://msdn.microsoft.com/en-us

问题 I'm using the AVX2 x86 256-bit SIMD extensions. I want to do a 32-bit integer component wise if-then-else instruction. In the Intel documentations such an instruction is called vblend. The Intel intrinsic guide contains the function _mm256_blendv_epi8. This function does nearly what I need. The only problem is that it works with 8-bit integers. Unfortunately there is no _mm256_blendv_epi32 in docs. My first question is: Why does this function not exist? My second question is: How to emulate

问题 I found that _mm256_log_ps can't be used with GCC7. Most common suggestions on stackoverflow is to use ICC or leveraging OpenCL SDK. After downloading SDK and extracting RPM file, there are three .so files: __ocl_svml_l9.so, __ocl_svml_e9.so, __ocl_svml_h8.so Can someone teach me how to call _mm256_log_ps with these .so files? Thank you. 回答1: You can use the log function from the Eigen library: #include <Eigen/Core> void foo(float* data, int size) { Eigen::Map<Eigen::ArrayXf> arr(data, size);

问题 I want to convert a vector of signed char into a vector of unsigned char. I want to preserve the value range for each type. I mean the value range of signed char is -128 and +127 when the value range of an unsigned char element is between 0 - 255. Without intrinsics I can do this almost like that : #include <iostream> int main(int argc,char* argv[]) { typedef signed char schar; typedef unsigned char uchar; schar a[]={-1,-2,-3,4,5,6,-7,-8,9,10,-11,12,13,14,15,16,17,-128,19,20,21,22,23,24,25,26

问题 I am trying to learn AVX instructions and while running a basic code I recieve Illegal instruction (core dumped) The code is mentioned below and I am compiling it using g++ -mavx512f 1.cpp What exactly is the problem and how to overcome it? Thank You! #include <immintrin.h> #include<iostream> using namespace std; void add(const float a[], const float b[], float res[], int n) { int i = 0; for(; i < (n&(~0x31)) ; i+=32 ) { __m512 x = _mm512_loadu_ps( &a[i] ); __m512 y = _mm512_loadu_ps( &b[i] )