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#include "Halide.h"
#include <math.h>
#include <stdio.h>
using namespace Halide;
// NB: You must compile with -rdynamic for llvm to be able to find the
// appropriate symbols
// Many things that are difficult to do with Halide can be hacked in
// using reductions that call extern C functions. In general this is a
// bad way to do things, because you've tied yourself to C, which
// means no GPU. Additionally, if your reduction has pure dimensions,
// you need to take care to make your extern functions
// thread-safe.
// Here we use an extern call to print an ascii-art Mandelbrot set.
int call_count = 0;
extern "C" HALIDE_EXPORT_SYMBOL int draw_pixel(int x, int y, int val) {
call_count++;
static int last_y = 0;
if (y != last_y) {
printf("\n");
last_y = y;
}
const char *code = " .:-~*={}&%#@";
if (val >= static_cast<int>(strlen(code))) {
val = static_cast<int>(strlen(code)) - 1;
}
printf("%c", code[val]);
return 0;
}
HalideExtern_3(int, draw_pixel, int, int, int);
// Make a complex number type using Tuples
class Complex {
Tuple t;
public:
Complex(Expr real, Expr imag)
: t(real, imag) {
}
Complex(Tuple tup)
: t(tup) {
}
Complex(FuncRef f)
: t(Tuple(f)) {
}
Expr real() const {
return t[0];
}
Expr imag() const {
return t[1];
}
operator Tuple() const {
return t;
}
};
// Define the usual complex arithmetic
Complex operator+(const Complex &a, const Complex &b) {
return Complex(a.real() + b.real(),
a.imag() + b.imag());
}
Complex operator-(const Complex &a, const Complex &b) {
return Complex(a.real() - b.real(),
a.imag() - b.imag());
}
Complex operator*(const Complex &a, const Complex &b) {
return Complex(a.real() * b.real() - a.imag() * b.imag(),
a.real() * b.imag() + a.imag() * b.real());
}
Complex conjugate(const Complex &a) {
return Complex(a.real(), -a.imag());
}
Expr magnitude(Complex a) {
return (a * conjugate(a)).real();
}
int main(int argc, char **argv) {
Var x, y;
Func mandelbrot;
// Use a different scale on x and y because terminal characters
// are not square. Arbitrarily chosen to fit the set nicely.
Complex initial(x / 20.0f, y / 8.0f);
Var z;
mandelbrot(x, y, z) = Complex(0.0f, 0.0f);
RDom t(1, 40);
Complex current = mandelbrot(x, y, t - 1);
mandelbrot(x, y, t) = current * current + initial;
// How many iterations until something escapes a circle of radius 2?
Func count;
Tuple escape = argmin(magnitude(mandelbrot(x, y, t)) < 4);
// If it never escapes, use the value 0
count(x, y) = select(escape[1], 0, escape[0]);
RDom r(-45, 71, -10, 21);
Func render;
render() += draw_pixel(r.x, r.y, count(r.x, r.y));
mandelbrot.compute_at(render, r.x);
render.realize();
printf("\n");
// Check draw_pixel was called the right number of times.
if (call_count != 71 * 21) {
printf("Something went wrong\n");
return 1;
}
printf("Success!\n");
return 0;
}
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