Halide (programming language)

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Halide
Paradigm functional, parallel
Designed by Jonathan Ragan-Kelley and Andrew Adams
Developer MIT, (with help from Stanford and Adobe)
First appeared 2012
Typing discipline static
Implementation language C++
OS Mac OS X (10.6 through 10.8), 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++.

Language[edit]

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[edit]

The following function defines and sets the schedule for a 3x3 box filter defined as a series of two 3x1 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[edit]

Google used Halide and TensorFlow for its Pixel 2 Pixel Visual Core.[2]

See also[edit]

References[edit]

External links[edit]