Simple examples of OpenCL code

Simple examples of OpenCL code, which I am using to learn heterogeneous and GPU computing with OpenCL.

Examples included

* -- reproduced to work in 2025 on AMD GPU

• *add_numbers: add a list of numbers together. Includes detailed error handling which makes the code harder to read and understand
• *square_array: computes array^2 (I am playing mostly with this one)
• *sum_array: sums two arrays
• cf4cl: testing OpenCL C wrapper
• *Hello_World: OpenCL "Hello World" by Apple
• *mandelbrot: my attempt at a simple Mandelbrot set calculation
• N-BodySimulation: Apple's N-body simulator which clearly illustrates the speedup gained by using the GPU. Requires Xcode
• RayTraced_Quaternion_Julia-Set_Example: Apple
• rng: Illustrates how to generate random numbers in the host and in the GPU using the library clRNG
• auger: generates random cosmic rays on an isotropic sky
• *waste: compute cycle waster

The examples that clearly demonstrate the computational advantage of using a GPU for processing are N-BodySimulation, RayTraced_Quaternion_Julia-Set_Example (both developed by Apple programmers) and auger. For auger, I got impressive speedups of >200x compared to a serial code on the CPU.

Info about OpenCL devices

To learn about your OpenCL devices, try:

clinfo

To install clinfo on MacOS:

brew install homebrew/science/clinfo

References

Slides

• OpenCL introduction, S. Grauer-Gray
• OpenCL introduction, F. Desprez

Code walkthroughs

• Vector addition in OpenCL (Oak Ridge National Lab)
• Getting started with OpenCL and GPU computing, by E. Smistad
• A gentle introduction to OpenCL, Dr. Dobbs. Includes interesting analogies, but may be too hard as a first read

Courses

• Hands-on OpenCL
• AMD OpenCL course
• Introduction to OpenCL, Manchester

Donate

If you are really happy with these examples, you can buy me a beer. Perhaps I could create a similar repo with CUDA examples?

TODO