https://github.com/jeffamstutz/tsimd

Fundamental C++ SIMD types for Intel CPUs (sse, avx, avx2, avx512)
https://github.com/jeffamstutz/tsimd

cpp cpp11 header-only simd simd-library

Last synced: 3 days ago
JSON representation

Fundamental C++ SIMD types for Intel CPUs (sse, avx, avx2, avx512)

• Host: GitHub
• URL: https://github.com/jeffamstutz/tsimd
• Owner: jeffamstutz
• License: mit
• Created: 2017-10-13T02:16:59.000Z (about 7 years ago)
• Default Branch: main
• Last Pushed: 2021-06-28T18:27:38.000Z (over 3 years ago)
• Last Synced: 2024-12-25T05:07:38.097Z (10 days ago)
• Topics: cpp, cpp11, header-only, simd, simd-library
• Language: C++
• Size: 604 KB
• Stars: 344
• Watchers: 25
• Forks: 20
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

README

        
# tsimd - Fundamental C++ SIMD types for Intel CPUs (sse to avx512)

This library is header-only and is implemented according to which Intel ISA

flags are enabled in the translation unit for which they are used (e.g. -mavx

with gcc or clang).

Master Status: [![Build Status](https://travis-ci.org/jeffamstutz/tsimd.svg?branch=master)](https://travis-ci.org/jeffamstutz/tsimd)

## TODOs (contributions welcome!)

- unsigned integer pack<> types

- support for other CPU ISAs

## Build Requirements

### Using tsimd

- C++11 compiler

(unofficial list of compilers, not all are tested)

* GCC >= 4.8.1

* clang >= 3.4

* ICC >= 16

* Visual Studio 2015 (64-bit target)

### Building tsimd's examples/benchmarks/tests and installing from soure

- cmake >= 3.2

## Library layout and usage

The library is logically composed of 3 different components:

1. The pack class, which is a _logical_ SIMD register

2. Functions which can load and store packs in and out of larger arrays.

3. Operators and functions to manipulate packs.

While there does not yet exist any true documentation, users are encouraged to

see what type aliases are defined in ```tsimd/detail/pack.h```, as well as what

operators and functions are available in ```tsimd/detail/operators/``` and

```tsimd/detail/functions/``` respectively. Generally speaking, each header

found in ```detail/``` encapsulates exactly one type, operator, or function to

aide in discovery.

## Example

### SAXPY

Consider the following function (kernel) taking values from two input arrays

and storing in an output array.

```cpp

// NOTE: n is the length of all 3 arrays

void saxpy(float a, int n, float x[], float y[], float out[])

{

  for (int i = 0; i < n; ++i) {

    const float xi = x[i];

    const float yi = y[i];

    const float result = a * xi + yi;

    out[i] = result;

  }

}

```

This kernel ends up applying the exact same formula to every element in the

data. SIMD instructions enable us to reduce the total number of iterations by a

factor of the CPU's SIMD register size. We do this by using tsimd types

instead of builtin types.

```cpp

// NOTE: n is the length of all 3 arrays

void saxpy_tsimd(float a, int n, float x[], float y[], float out[])

{

  using namespace tsimd;

  for (int i = 0; i < n; i += vfloat::static_size) {

    const vfloat xi = load(&x[i]);

    const vfloat yi = load(&y[i]);

    const vfloat result = a * xi + yi; // same formula!

    store(result, &out[i]);

  }

}

```

The advantage to this version (instead of using a specific SIMD width, say

```vfloat4``` or ```vfloat8```) is that the kernel function will be "widened"

to the best available width based on how it gets compiled. In other words:

4-wide for SSE, 8-wide for AVX/AVX2, and 16-wide for AVX512.