Halide (programming language)

HalideParadigm| functional, parallel

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Designed by| Jonathan Ragan-Kelley and Andrew Adams
Developer| MIT, (with help from Stanford, Google, and Adobe)
First appeared| 2012
Typing discipline| static
Implementation language| C++
OS| Mac OS, mainstream Linux distributions, Windows
Website| http://halide-lang.org/

Halide is a computer programming language designed for writing digital image processing code that takes advantage of memory locality, vectorized computation and multi-core CPUs and GPUs.[1] Halide is implemented as an internal domain-specific language (DSL) in C++.

## Contents

* 1 Language
* 2 Sample source code
* 3 Use
* 4 See also
* 5 References
* 6 External links

## Language

The main innovation Halide brings is the separation of the algorithm being implemented from its execution schedule, i.e. code specifying the loop nesting, parallelization, loop unrolling and vector instruction. These two are usually interleaved together and experimenting with changing the schedule requires the programmer to rewrite large portions of the algorithm with every change. With Halide, changing the schedule does not require any changes to the algorithm and this allows the programmer to experiment with scheduling and finding the most efficient one.

## Sample source code

The following function defines and sets the schedule for a 3×3 box filter defined as a series of two 3×1 passes:

Func blur_3x3(Func input) {
Func blur_x, blur_y;
Var x, y, xi, yi;

// The algorithm - no storage or order
blur_x(x, y) = (input(x-1, y) + input(x, y) + input(x+1, y))/3;
blur_y(x, y) = (blur_x(x, y-1) + blur_x(x, y) + blur_x(x, y+1))/3;

// The schedule - defines order, locality; implies storage
blur_y.tile(x, y, xi, yi, 256, 32)
.vectorize(xi, 8).parallel(y);
blur_x.compute_at(blur_y, x).vectorize(x, 8);

return blur_y;

## Use

Google used Halide and TensorFlow for its Pixel 2 Pixel Visual Core.[2] Adobe Photoshop also uses Halide.[3] Both Google and Adobe have been involved in Halide research.[4]

## See also

* Cuneiform (programming language)
* Algorithmic skeleton
* Parallel programming model

## References

1. ↑ "Halide - New Language For Image Processing". 2012. http://www.i-programmer.info/news/192-photography-a-imaging/4588-halide-new-language-for-image-processing.html. Retrieved 20 September 2013.
2. ↑ "Google and Intel cook AI chips, neural network exchanges – and more". Situation Publishing. https://www.theregister.co.uk/2017/10/22/ai_roundup/.
3. ↑ "Photoshop freezing at startup on Halide Bottlenecks". 2020. https://community.adobe.com/t5/photoshop/photoshop-freezing-at-startup-on-halide-bottlenecks/td-p/11085284?page=1. Retrieved 27 April 2020.
4. ↑ "Learning to Optimize Halide with Tree Search and Random Programs". 2019. https://halide-lang.org/papers/halide_autoscheduler_2019.pdf. Retrieved 1 July 2019.

## External links

* http://halide-lang.org/
* Decoupling Algorithms from Schedules for Easy Optimization of Image Processing Pipelines
* "Halide: A Language and Compiler for Optimizing Parallelism, Locality, and Recomputation in Image Processing Pipelines". http://people.csail.mit.edu/jrk/halide-pldi13.pdf. (8,259 KB)

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