I've implemented the following program for convolution matrix #include <stdio.h> #include <time.h> #define NUM_LOOP 1000 #define N 128 //input or output dimention 1 #define M N //inp...

I have the following C code. The first part just reads in a matrix of complex numbers from standard in into matrix called M. The interesting part is the second part. #include <stdio.h> #incl...

I have a simple loop with takes the product of n complex numbers. As I perform this loop millions of times I want it to be as fast as possible. I understand that it's possible to do this quickly us...

Initially investigating the effect of the #pragma omp simd directive, I came across a behaviour that I cannot explain, related to the vectorization of a simple for loop. The following code sample c...

Does the new RyuJIT compiler ever generate vector (SIMD) CPU instructions, and when? Side note: The System.Numerics namespace contains types that allow explicit use of Vector operations which may ...

Looking around here and the internet, I can find a lot of posts about modern compilers beating SSE in many real situations, and I have just encountered in some code I inherited that when I disable ...

Let's say I have a function written in c++ that performs matrix vector multiplications on a lot of vectors. It takes a pointer to the array of vectors to transform. Am I correct to assume that the ...

I am compiling my code using following command: gcc -O3 -ftree-vectorizer-verbose=6 -msse4.1 -ffast-math With this all the optimizations are enabled. But I want to disable vectorization while ...

With the GCC compiler, the -ftree-vectorize option turns on auto-vectorization, and this flag is automatically set when using -O3. To what level does it vectorize? I.e., will I get SSE2, SSE4.2, AV...

For the following loop GCC will only vectorize the loop if I tell it to use associative math e.g. with -Ofast. float sumf(float *x) { x = (float*)__builtin_assume_aligned(x, 64); float sum = 0; ...

I've spent the past few days reading about autovectorization with gcc 4.7. I followed some examples I saw online, and the setup seems to be correct. But when I actually run with the code and compar...

Consider the following minimal example: #cython: language_level=3, boundscheck=False, wraparound=False, initializedcheck=False, cdivision=True cimport cython from libc.stdlib cimport malloc def ma...

Consider the following example of doing an inplace-add on a Cython memoryview: #cython: boundscheck=False, wraparound=False, initializedcheck=False, nonecheck=False, cdivision=True from libc.stdli...

I am trying to learn gcc auto-vectorization module. After reading documentation from here. Here is what I tried (debian jessie amd64): $ cat ex1.c int a[256], b[256], c[256]; foo () { int i; f...

I am exploring how different implementations of simple loops in C99 auto-vectorize based upon the function signature. Here is my code: /* #define PRAGMA_SIMD _Pragma("simd") */ #define PRAGMA_SIM...

Arstechnia recently had an article Why are some programming languages faster than others. It compares Fortran and C and mentions summing arrays. In Fortran it's assumed that arrays don't overlap so...

The v4 series of the gcc compiler can automatically vectorize loops using the SIMD processor on some modern CPUs, such as the AMD Athlon or Intel Pentium/Core chips. How is this done?