ex2!: 3 times height

exercise2/Makefile

@@ -10,17 +10,16 @@ NPROC   := 3
 
 .PHONY: all clean run
 
-all: clean run
+all: parallel
 
 $(TARGET): $(SRC)
-	mkdir -p $(OUTDIR)
 	$(CC) $(CFLAGS) -o $(OUT) $<
 
 run: $(TARGET)
 	cd $(OUTDIR) && ./$< $(ARGS)
 
 clean:
-	rm -rf $(OUTDIR)
+	rm -rf $(OUTDIR)/*
 
 time: $(TARGET)
 	python3 bench.py './$(OUT) 0' $(NBENCH)

exercise2/mandel_mpi.c

@@ -2,6 +2,7 @@
 #include <mpi.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #define XSIZE 2560
 #define YSIZE 2048
@@ -22,6 +23,8 @@ typedef struct {
   double real, imag;
 } complex_t;
 
+int rank, size;
+
 void calculate() {
   for (int i = 0; i < XSIZE; i++) {
     for (int j = 0; j < YSIZE; j++) {
@@ -83,36 +86,53 @@ void fancycolour(uchar *p, int iter) {
 
 int main(int argc, char **argv) {
   MPI_Init(&argc, &argv);
-  int rank, size;
   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
   MPI_Comm_size(MPI_COMM_WORLD, &size);
-  printf("hello from rank %d/%d", rank, size);
-  if (argc == 1) {
-    puts("Usage: MANDEL n");
-    puts("n decides whether image should be written to disk (1=yes, 0=no)");
-    return 0;
-  }
-  /* Calculate the range in the y-axis such that we preserve the
-     aspect ratio */
+
   step = (xright - xleft) / XSIZE;
-  yupper = ycenter + (step * YSIZE) / 2;
-  ylower = ycenter - (step * YSIZE) / 2;
+  double old_yupper = ycenter + (step * YSIZE) / 2;
+  double old_ylower = ycenter - (step * YSIZE) / 2;
+  double delta = (old_yupper - old_ylower) / size;
+
+  ylower = old_ylower + rank * delta;
+  yupper = old_ylower + (rank + 1) * delta;
 
   calculate();
 
-  if (strtol(argv[1], NULL, 10) != 0) {
-    /* create nice image from iteration counts. take care to create it upside
-       down (bmp format) */
-    unsigned char *buffer = calloc(XSIZE * YSIZE * 3, 1);
-    for (int i = 0; i < XSIZE; i++) {
-      for (int j = 0; j < YSIZE; j++) {
-        int p = ((YSIZE - j - 1) * XSIZE + i) * 3;
-        fancycolour(buffer + p, pixel[PIXEL(i, j)]);
-      }
+  printf("after calculate %d\n", rank);
+
+  const int bufsize = XSIZE * YSIZE * 3;
+  unsigned char *buffer = calloc(bufsize, 1);
+  for (int i = 0; i < XSIZE; i++) {
+    for (int j = 0; j < YSIZE; j++) {
+      int p = ((YSIZE - j - 1) * XSIZE + i) * 3;
+      fancycolour(buffer + p, pixel[PIXEL(i, j)]);
     }
-    /* write image to disk */
-    savebmp("mandel.bmp", buffer, XSIZE, YSIZE);
   }
+
+  printf("after buffer %d\n", rank);
+
+  if (rank != 0)
+    MPI_Send(buffer, bufsize, MPI_INT8_T, 0, 0, MPI_COMM_WORLD);
+
+  printf("hello again from %d\n", rank);
+
+  // use process 0 as central process: gather calulations and output image
+  if (rank == 0) {
+    unsigned char *bufferest = calloc(bufsize * size, 1);
+    memcpy(bufferest, buffer, bufsize);
+    printf("after memcpy\n");
+
+    for (int i = 1; i < size; i++) {
+      MPI_Recv(buffer, bufsize, MPI_INT8_T, i, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+      memcpy(bufferest + bufsize * i, buffer, bufsize);
+    }
+    printf("after loop\n");
+
+    savebmp("mandel.bmp", buffer, XSIZE, YSIZE * size);
+    printf("after save\n");
+  }
+
   MPI_Finalize();
   return 0;
 }