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# Intel® Implicit SPMD Program Compiler (Intel® ISPC)

`ispc` is a compiler for a variant of the C programming language, with
extensions for [single program, multiple
data](http://en.wikipedia.org/wiki/SPMD) programming.  Under the SPMD model,
the programmer writes a program that generally appears to be a regular serial
program, though the execution model is actually that a number of *program
instances* execute in parallel on the hardware.

## Overview

`ispc` compiles a C-based SPMD programming language to run on the SIMD units of
CPUs and GPUs; it frequently provides a 3x or more speedup on architectures
with 4-wide vector SSE units and 5x-6x on architectures with 8-wide AVX vector
units, without any of the difficulty of writing intrinsics code.
Parallelization across multiple cores is also supported by `ispc`, making it
possible to write programs that achieve performance improvement that scales by
both number of cores and vector unit size.

There are a few key principles in the design of `ispc`:

  * To build a small set of extensions to the C language that would deliver
    excellent performance to performance-oriented programmers who want to run
    SPMD programs on the CPU and GPU.

  * To provide a thin abstraction layer between the programmer and the
    hardware--in particular, to have an execution and data model where the
    programmer can cleanly reason about the mapping of their source program to
    compiled assembly language and the underlying hardware.

  * To make it possible to harness the computational power of SIMD vector units
    without the extremely low-programmer-productivity activity of directly
    writing intrinsics.

  * To explore opportunities from close coupling between C/C++ application code
    and SPMD `ispc` code running on the same processor--to have lightweight
    function calls between the two languages and to share data directly via
    pointers without copying or reformatting.

`ispc` is an open source compiler with the BSD license.  It uses the remarkable
[LLVM Compiler Infrastructure](http://llvm.org) for back-end code generation
and optimization and is [hosted on github](http://github.com/ispc/ispc). It
supports Windows, macOS, and Linux as a host operating system and also capable
to target Android, iOS, and PS4/PS5.  It currently supports multiple flavours
of x86 (SSE2, SSE4, AVX, AVX2, and AVX512), ARM (NEON), and Intel® GPU
architectures (Gen9 and Xe family).

## Features

`ispc` provides a number of key features to developers:

  * Familiarity as an extension of the C programming language: `ispc` supports
    familiar C syntax and programming idioms, while adding the ability to write
    SPMD programs.

  * High-quality SIMD code generation: the performance of code generated by
    `ispc` is often close to that of hand-written intrinsics code.

  * Ease of adoption with existing software systems: functions written in
    `ispc` directly interoperate with application functions written in C/C++
    and with application data structures.
            
  * Portability across over a decade of CPU generations: `ispc` has targets for
    x86 SSE2, SSE4, AVX, AVX2, and AVX512, as well as ARM NEON and recent
    Intel® GPUs.

  * Portability across operating systems: Microsoft Windows, macOS, Linux, and
    FreeBSD are all supported by `ispc`.

  * Debugging with standard tools: `ispc` programs can be debugged with
    standard debuggers.

## Installation
### Official Release Binaries

You can download the official release binaries from [the release
page](https://github.com/ispc/ispc/releases). Choose the appropriate version
for your operating system and architecture.

### Linux (Snap Store)

Linux users can install `ispc` using the Snap Store:

```bash
snap install ispc
```

### Intel® oneAPI Distribution

`ispc` is distributed as part of the Intel® oneAPI. You can install it from the
corresponding repositories for DEB-based and RPM-based Linux distributions.
Follow the instructions below:

DEB-based Linux (Ubuntu, Debian, etc.)
First, download the key to the system keyring:

```bash
wget -O- https://apt.repos.intel.com/intel-gpg-keys/GPG-PUB-KEY-INTEL-SW-PRODUCTS.PUB | gpg --dearmor | sudo tee /usr/share/keyrings/oneapi-archive-keyring.gpg > /dev/null
```

Next, add the signed entry to apt sources and configure the APT client to use
the Intel repository:

```bash
echo "deb [signed-by=/usr/share/keyrings/oneapi-archive-keyring.gpg] https://apt.repos.intel.com/oneapi all main" | sudo tee /etc/apt/sources.list.d/oneAPI.list
```

Update the package list and install `ispc`:

```bash
sudo apt-get update
sudo apt-get install intel-oneapi-ispc
```

The installation location is inside the `/opt/intel/` directory. To use `ispc`,
either use the full path `/opt/intel/oneapi/ispc/latest/bin/ispc` or add the
`bin`  directory to your `PATH`:

```bash
source /opt/intel/oneapi/ispc/latest/env/vars.sh
```

### Other Package Managers

Thanks to community support, `ispc` is also available through a variety of
package managers on multiple operating systems.

## Additional Resources

Latest `ispc` binaries corresponding to `main` branch can be downloaded from
Appveyor for
[Linux](https://ci.appveyor.com/api/projects/ispc/ispc/artifacts/build%2Fispc-trunk-linux.tar.gz?job=Environment%3A%20APPVEYOR_BUILD_WORKER_IMAGE%3DUbuntu1804%2C%20LLVM_VERSION%3Dlatest)
and
[Windows](https://ci.appveyor.com/api/projects/ispc/ispc/artifacts/build%2Fispc-trunk-windows.zip?job=Environment%3A%20APPVEYOR_BUILD_WORKER_IMAGE%3DVisual%20Studio%202019%2C%20LLVM_VERSION%3Dlatest)
See also additional [documentation](https://ispc.github.io/documentation.html)
and additional [performance information](https://ispc.github.io/perf.html).  If
you have a bug report and have a question, you are welcome to open an
[issue](https://github.com/ispc/ispc/issues) or start a
[discussion](https://github.com/ispc/ispc/discussions) on GitHub.
