A stupid way to compute the mandelbrot iteration in Halide (https://github.com/halide/Halide).

mandelbrot.cpp

/*
 * Build as
 * g++ mandelbrot.cpp -I /path/to/Halide/include -I /path/to/Halide/apps /path/to/libHalide.a \
 *        -o mandel -lpthread -ldl -L/usr/lib/x86_64-linux-gnu -lpng12 -I/usr/include/libpng12
 */

#include <Halide.h>
using namespace Halide;
#include <support/image_io.h>
#include <time.h>
#include <iostream>


Var x, y, l, c;
inline Func mandel_step(Func f, Func m0) {
  Func g;
  Expr r = f(x, y, 0);
  Expr i = f(x, y, 1);
  g(x, y, l) = select(l == 0,
      pow(r, 2) - pow(i, 2) + m0(x,y, 0),
      2 * r * i + m0(x,y, 1));
  return g;
}

int main() {
  const int n_iter = 50;
  const int dim = 5000;
  Expr scale = static_cast<float>(dim)/4;
  Func m0("m0"), mandelbrot("mandel");

  m0(x, y, l) = select(l == 0, x - dim/2, y - dim/2)/scale;
  m0.compute_root();

  Func m[n_iter];

  m[0](x, y, l) = m0(x, y, l);

  for (int i = 1; i < n_iter; i++) {
    m[i](x, y, l)  = clamp(mandel_step(m[i-1], m0)(x, y, l), -4.f, 4.f);
  }

  mandelbrot(x, y, c) = clamp(m[n_iter-1](x, y, c), 0.f, 1.f);

  mandelbrot.parallel(x);

  clock_t t0 = clock();
  mandelbrot.compile_jit();
  clock_t t1 = clock();

  std::cout << "time to compile: " << t1 - t0 << std::endl;

  Image<float> output = mandelbrot.realize(dim, dim, 3);
  clock_t t2 = clock();
  std::cout << "time to process: " << t2 - t1 << std::endl;

  save(output, "mandelbrot.png");
}