add an openmp version of multibrot
parent
ffa93c8d34
commit
341990f1ee
@ -0,0 +1,202 @@
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#include <assert.h>
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#include <complex.h>
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#include <getopt.h>
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#include <stdbool.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <png.h>
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#include <pthread.h>
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typedef uint32_t pixel_t;
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typedef struct {
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pixel_t *pixels;
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size_t width;
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size_t height;
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} bitmap_t;
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/* The maximum iteration count. */
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const int max_it = 170;
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/**
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* Compute the out-coloring based on the iteration counter.
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*
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* Out-coloring means: coloring when a pixel is determined
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* to be outside of the mandelbrot set.
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*
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* @param it iteration counter when diversion was determined.
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*
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* @return pixel color
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*/
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pixel_t outcolor(int it) {
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return 0x00010001 * ((it * 0xff) / max_it);
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}
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/**
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* "Compute" the in-coloring.
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*
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* In-coloring means: coloring when a pixel is determined
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* to be inside the mandelbrot set.
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*
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* @return pixel, i.e. color
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*/
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pixel_t incolor() {
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return 0x00000000; /* black */
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}
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/* Computes the visual representation of a mandelbrot set for a given line. */
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void compmandelbrot_line(bitmap_t * mbrot, size_t y) {
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for (size_t x = 0; x < mbrot->width; x++) {
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float complex c = ((3.0f * x / mbrot->width) - 2.0f)
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+ I * ((2.0f * y / mbrot->height) - 1.0f);
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bool diverges = false;
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float complex z = 0;
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int it;
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for (it = 1; it <= max_it; it++) {
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/* z = z² + c */
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z = cpowf(z, 2) + c;
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/* If |z| ever gets greater than 2, it diverges. */
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if (cabsf(z) > 2) {
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diverges = true;
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break;
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}
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}
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uint32_t color;
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if (diverges) {
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color = outcolor(it);
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} else {
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color = incolor();
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}
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size_t i = y * mbrot->width + x;
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mbrot->pixels[i] = color;
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}
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}
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/* Mandelbrot bitmap. */
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bitmap_t *mbrot;
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/**
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* Writes a bitmap to a PNG file.
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*
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* @param bitmap bitmap to save
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* @param path PNG file to write to
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*
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* @return 0 on success, non-zero on error.
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*/
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static int save_png_to_file(bitmap_t * bitmap, const char *path) {
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FILE *fp;
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png_structp png_ptr = NULL;
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png_infop info_ptr = NULL;
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size_t x, y;
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png_byte **row_pointers = NULL;
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/* "status" contains the return value of this function. At first it is set to
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* a value which means 'failure'. When the routine has finished its work, it
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* is set to a value which means 'success'. */
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int status = -1;
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int pixel_size = 3;
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int depth = 8;
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fp = fopen(path, "wb");
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if (!fp) {
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goto fopen_failed;
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}
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png_ptr =
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png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
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if (png_ptr == NULL) {
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goto png_create_write_struct_failed;
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}
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info_ptr = png_create_info_struct(png_ptr);
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if (info_ptr == NULL) {
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goto png_create_info_struct_failed;
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}
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/* Set up error handling. */
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if (setjmp(png_jmpbuf(png_ptr))) {
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goto png_failure;
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}
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/* Set image attributes. */
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png_set_IHDR(png_ptr,
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info_ptr,
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bitmap->width,
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bitmap->height,
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depth,
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PNG_COLOR_TYPE_RGB,
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PNG_INTERLACE_NONE,
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PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
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/* Initialize rows of PNG. */
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row_pointers = png_malloc(png_ptr, bitmap->height * sizeof(png_byte *));
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for (y = 0; y < bitmap->height; ++y) {
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png_byte *row =
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png_malloc(png_ptr, sizeof(uint8_t) * bitmap->width * pixel_size);
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row_pointers[y] = row;
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for (x = 0; x < bitmap->width; ++x) {
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pixel_t *pixel = bitmap->pixels + (y * bitmap->width + x);
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*row++ = (*pixel & 0x00ff0000) >> 16;
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*row++ = (*pixel & 0x0000ff00) >> 8;
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*row++ = (*pixel & 0x000000ff);
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}
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}
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/* Write the image data to "fp". */
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png_init_io(png_ptr, fp);
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png_set_rows(png_ptr, info_ptr, row_pointers);
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png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
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/* The routine has successfully written the file, so we set "status" to a
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* value which indicates success. */
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status = 0;
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for (y = 0; y < bitmap->height; y++) {
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png_free(png_ptr, row_pointers[y]);
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}
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png_free(png_ptr, row_pointers);
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png_failure:
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png_create_info_struct_failed:
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png_destroy_write_struct(&png_ptr, &info_ptr);
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png_create_write_struct_failed:
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fclose(fp);
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fopen_failed:
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return status;
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}
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int main() {
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/* Set up mandelbrot bitmap. */
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mbrot = calloc(sizeof(bitmap_t), 1);
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mbrot->width = 1600;
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mbrot->height = 1200;
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mbrot->pixels = calloc(sizeof(pixel_t), mbrot->width * mbrot->height);
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assert(mbrot->pixels != NULL);
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/* Compute. */
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#pragma omp parallel for
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for (unsigned int y = 0; y < mbrot->height; y++) {
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compmandelbrot_line(mbrot, y);
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}
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/* Save PNG. */
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char *file = "multibrot-openmp.png";
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int ret = save_png_to_file(mbrot, file);
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assert(ret == 0);
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/* Clean up. */
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free(mbrot->pixels);
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free(mbrot);
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return 0;
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}
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