Halide simple example

halide-schedule.cpp

// Modified from tutorials/lesson_02.cpp and test/vectorize.cpp

// On linux, you can compile and run it like so:
// g++ -I ../include -L ../bin -lHalide -lpthread -ldl -lpng blur.cpp
// LD_LIBRARY_PATH=../bin ./lesson_02 

// On os x:
// g++ -I ../include -L ../bin -lHalide `libpng-config --cflags --ldflags` blur.cpp
// DYLD_LIBRARY_PATH=../bin ./lesson_02 

// The only Halide header file you need is Halide.h. It includes all of Halide.
#include <Halide.h>

using Halide::Image;

#ifdef _WIN32
extern "C" bool QueryPerformanceCounter(uint64_t *);
extern "C" bool QueryPerformanceFrequency(uint64_t *);
double currentTime() {
    uint64_t t, freq;
    QueryPerformanceCounter(&t);
    QueryPerformanceFrequency(&freq);
    return (t * 1000.0) / freq;
}
#else
#include <sys/time.h>
double currentTime() {
    timeval t;
    gettimeofday(&t, NULL);
    return t.tv_sec * 1000.0 + t.tv_usec / 1000.0f;
}
#endif

#include "../apps/support/image_io.h"

int main(int argc, char **argv) {

    Halide::Image<uint8_t> image = load<uint8_t>("../apps/images/rgb.png");
    Halide::Func brighter,brighter_par;

    Halide::Var x, y, xi, yi, c;

    Halide::Func input;

    int w = image.width();
    int h = image.height();
    int ch = image.channels();

    printf("Input: %d x %d x %d\n",w,h,ch);

    //Define algorithm.
    brighter(x, y, c) = Halide::cast<uint8_t>(min(image(x, y, c) * 1.5f, 255));

    brighter_par(x,y,c) = brighter(x,y,c);

    // Specify a schedule.
    brighter_par.split(y, y, yi, 8).parallel(y).vectorize(x, 8);
    // brighter_par.vectorize(x,4).parallel(y);

    //By invoking "realize" first, JIT is done before time measurement. (JIT takes a few seconds.)
    Image<uint8_t> out = brighter.realize(w,h,ch);
    Image<uint8_t> out_par = brighter_par.realize(w,h,ch);

    printf("Start measurement.\n");

    //Execution time measurement.
    double t1 = currentTime();
    const int repeat = 1000;
    for (int i = 0; i < repeat; i++) {
        brighter.realize(out);
    }
    double t2 = currentTime();
    for (int i = 0; i < repeat; i++) {
        brighter_par.realize(out_par);
    }
    double t3 = currentTime();

    printf("Vectorized vs scalar (average over %d times): %.2f ms %.2f ms. Speedup = %1.3f\n", repeat,
        ((t3-t2)/repeat), ((t2-t1)/repeat), (t2-t1)/(t3-t2));

    save(out, "brighter.png");
    save(out_par, "brighter_par.png");
    
    printf("Success!\n");
    return 0;
}