add an openmp version of mandelbrot.c

.gitignore

@@ -31,3 +31,4 @@ undefined-behaviour
 multibrot-openmp
 multibrot-openmp.png
 hello-openmp
+mandelbrot-openmp

Makefile

@@ -5,7 +5,7 @@ CFLAGS=-std=c99 -Wextra -pedantic -g -O0
 CC_OPENMP=gcc # no OpenMP in our clang
 CFLAGS_OPENMP=$(CFLAGS) -fopenmp
 
-TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs ncurses-pong bit-fuckery bit-fuckery2 checkcheck multibrot bloom wo-lernen lua-foo binsearch test-inline-assembly uiowa-threads-example mtrace-test av-variance undefined-behaviour multibrot-openmp hello-openmp
+TARGETS=approximate-pi linked-list mandelbrot threads circular-buffer structs ncurses-pong bit-fuckery bit-fuckery2 checkcheck multibrot bloom wo-lernen lua-foo binsearch test-inline-assembly uiowa-threads-example mtrace-test av-variance undefined-behaviour multibrot-openmp hello-openmp mandelbrot-openmp
 EXTRAS=mandelbrot.bmp multibrot.png test-inline-assembly.s tags mtrace-test.trace mtrace-test.txt
 
 .PHONY: all
@@ -72,3 +72,6 @@ hello-openmp: hello-openmp.c
 
 multibrot-openmp: multibrot-openmp.c
 	$(CC_OPENMP) $(CFLAGS_OPENMP) -o $@ $< -lm -lpng
+
+mandelbrot-openmp: mandelbrot-openmp.c
+	$(CC_OPENMP) $(CFLAGS_OPENMP) $(shell sdl-config --cflags) -o $@ $< $(shell sdl-config --libs) -lm

mandelbrot-openmp.c

@@ -0,0 +1,93 @@
+#include "SDL.h"
+#include <complex.h>
+#include <stdbool.h>
+
+/* The maximum iteration count. */
+const int max_it = 170;
+
+/* Compute the out-coloring based on the iteration counter. */
+Uint32 outcolor(int it) {
+  return 0x00010001 * ((it * 0xff) / max_it);
+}
+
+/* "Compute" the in-coloring. */
+Uint32 incolor() {
+  return 0x00000000;            /* black */
+}
+
+void drawmandelbrot(SDL_Surface * surface) {
+  if (SDL_MUSTLOCK(surface)) {
+    SDL_LockSurface(surface);
+  }
+  Uint32 *pixels = (Uint32 *) surface->pixels;
+
+  #pragma omp parallel for
+  for (int i = 0; i < surface->w * surface->h; i++) {
+    int y = i / surface->w;
+    int x = i % surface->w;
+
+    float complex c = ((3.0f * x / surface->w) - 2.0f)
+        + I * ((2.0f * y / surface->h) - 1.0f);
+
+    bool diverges = false;
+    float complex z = 0;
+    int it;
+    for (it = 1; it <= max_it; it++) {
+      /* z = z² + c */
+      z = cpowf(z, 2) + c;
+
+      /* If |z| ever gets greater than 2, it diverges. */
+      if (cabsf(z) > 2) {
+        diverges = true;
+        break;
+      }
+    }
+
+    Uint32 color;
+    if (diverges) {
+      color = outcolor(it);
+    } else {
+      color = incolor();
+    }
+
+    pixels[i] = color;
+
+    /* Update the screen every 10 lines. */
+    #pragma omp critical
+      {
+      if (y % 10 == 0 && x == 0) {
+        SDL_Flip(surface);
+      }
+    }
+  }
+
+  /* Update the screen a final time. */
+  SDL_Flip(surface);
+  if (SDL_MUSTLOCK(surface)) {
+    SDL_UnlockSurface(surface);
+  }
+}
+
+int main(void) {
+  /* Set up SDL. */
+  if (SDL_Init(SDL_INIT_EVERYTHING) < 0) {
+    fprintf(stderr, "Error: Could not initialize SDL: %s.\n",
+            SDL_GetError());
+    exit(1);
+  }
+  SDL_Surface *screen = SDL_SetVideoMode(1024, 768, 32, SDL_SWSURFACE);
+
+  /* Do the mandelbrot. */
+  drawmandelbrot(screen);
+
+  /* Save BMP */
+  char *file = "mandelbrot.bmp";
+  if (SDL_SaveBMP(screen, file) != 0) {
+    fprintf(stderr, "Could not write %s!\n", file);
+  }
+
+  /* Quit. */
+  /* FIXME: wait for key press here */
+  SDL_Delay(0*20000);
+  SDL_Quit();
+}