From 8533db7eb203a60510df020079fb7c20ec35ee78 Mon Sep 17 00:00:00 2001
From: Michael Zhang <mail@mzhang.io>
Date: Sun, 29 Oct 2023 21:34:22 +0000
Subject: [PATCH] progress

---
 assignments/02/.clangd    |   2 +-
 assignments/02/.gitignore |   4 +-
 assignments/02/Makefile   |   2 +-
 assignments/02/output.txt |   0
 assignments/02/qs_mpi.c   | 130 +++++++++++++++++++++++++++++++++++++-
 5 files changed, 134 insertions(+), 4 deletions(-)
 create mode 100644 assignments/02/output.txt

diff --git a/assignments/02/.clangd b/assignments/02/.clangd
index 26c50d3..d81ad1a 100644
--- a/assignments/02/.clangd
+++ b/assignments/02/.clangd
@@ -1,2 +1,2 @@
 CompileFlags:
-    Add: -I/usr/lib/aarch64-linux-gnu/openmpi/include -I/usr/lib/aarch64-linux-gnu/openmpi/include/openmpi
\ No newline at end of file
+    Add: -I/usr/lib/aarch64-linux-gnu/openmpi/include -I/usr/lib/aarch64-linux-gnu/openmpi/include/openmpi
diff --git a/assignments/02/.gitignore b/assignments/02/.gitignore
index 63654be..acc2ba1 100644
--- a/assignments/02/.gitignore
+++ b/assignments/02/.gitignore
@@ -1,2 +1,4 @@
 qs_mpi
-*.o
\ No newline at end of file
+*.o
+compile_commands.json
+.cache
\ No newline at end of file
diff --git a/assignments/02/Makefile b/assignments/02/Makefile
index 2053b2b..d6919cd 100644
--- a/assignments/02/Makefile
+++ b/assignments/02/Makefile
@@ -11,7 +11,7 @@ LDFLAGS += $(shell pkg-config --libs mpi)
 all: qs_mpi
 
 qs_mpi: qs_mpi.o
-	$(CC) $(LDFLAGS) -o $@ $^
+	$(CC) $^ $(CFLAGS) $(LDFLAGS) -o $@
 
 qs_mpi.o: qs_mpi.c
 	$(CC) $(CFLAGS) -c -o $@ $^
diff --git a/assignments/02/output.txt b/assignments/02/output.txt
new file mode 100644
index 0000000..e69de29
diff --git a/assignments/02/qs_mpi.c b/assignments/02/qs_mpi.c
index bb8adaf..01a66fd 100644
--- a/assignments/02/qs_mpi.c
+++ b/assignments/02/qs_mpi.c
@@ -1,6 +1,134 @@
 #include <mpi.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void local_quicksort(int *arr, int lo, int hi);
+char *string_of_list(int *arr, int len);
 
 int main(int argc, char **argv) {
-  //
+  int rank, p;
   MPI_Init(&argc, &argv);
+
+  int n = atoi(argv[1]);
+
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+  MPI_Comm_size(MPI_COMM_WORLD, &p);
+
+  // Generate integers
+  int n_over_p = n / p;
+  int integers[n_over_p];
+
+  // Important implementation detail: srand(0) is specially handled by glibc to
+  // behave as if it was called with srand(1). To get around this, I'm seeding
+  // with rank + 1
+  //
+  // See more: https://stackoverflow.com/a/27386563
+  srand(rank + 1);
+
+  for (int i = 0; i < n_over_p; ++i) {
+    // TODO: For readability during debugging, I'm capping this
+    integers[i] = rand() % 101;
+    // printf(" - %d\n", integers[i]);
+  }
+
+  int group_root = 0;
+
+  // Locally sort
+  printf("[%d] Numbers before:           %s\n", rank,
+         string_of_list(integers, n_over_p));
+  local_quicksort(integers, 0, n_over_p);
+  printf("[%d] Numbers after first sort: %s\n", rank,
+         string_of_list(integers, n_over_p));
+
+  // Select a pivot.
+  // This pivot is broadcasted to all nodes
+  int pivot;
+
+  // The pivot is selected as the median (see chp. 9.4.4)
+  // Not the real median though, need an existing element of the array
+  pivot = integers[n_over_p / 2];
+  MPI_Bcast(&pivot, 1, MPI_INT, 0, MPI_COMM_WORLD);
+
+  printf("Median: %d\n", pivot);
+
+  // Determine where the boundary between S (lower) and L (higher) lies
+  int boundary;
+  for (int i = 0; i < n_over_p; ++i) {
+    if (integers[i] >= pivot) {
+      boundary = i;
+      break;
+    }
+  }
+  int S_lo = 0, S_hi = boundary - 1;
+  int L_lo = boundary, L_hi = n_over_p - 1;
+  int S_size = S_hi - S_lo + 1, L_size = L_hi - L_lo + 1;
+  // printf("[%d] S: [%d - %d] (%d), L: [%d - %d] (%d)\n", rank, S_lo, S_hi,
+  //        S_size, L_lo, L_hi, L_size);
+
+  // Perform global arrangement
+  int S_global_end, L_global_end;
+  MPI_Scan(&S_size, &S_global_end, 1, MPI_INT, MPI_SUM, MPI_COMM_WORLD);
+  MPI_Scan(&L_size, &L_global_end, 1, MPI_INT, MPI_SUM, MPI_COMM_WORLD);
+
+  int S_global_start = S_global_end - S_size,
+      L_global_start = L_global_end - L_size;
+  printf("[%d] S: [%d - %d], L: [%d - %d]\n", rank, S_global_start,
+         S_global_end - 1, L_global_start, L_global_end - 1);
+
+  // Send it to the correct target
+
+  // The first node is responsible for collecting all the data and then printing
+  // it out to the file
+  // MPI_Gather(const void *sendbuf, int sendcount, MPI_INT, void *recvbuf,
+  //            int recvcount, MPI_INT, 0, MPI_COMM_WORLD);
+  if (rank == 0) {
+    FILE *f = fopen(argv[2], "w");
+    fclose(f);
+  }
+
+  MPI_Finalize();
+  return 0;
 }
+
+// hi not inclusive
+void local_quicksort(int *arr, int lo, int hi) {
+  int temp;
+
+  if (lo >= hi || lo < 0)
+    return;
+
+  int pivot = arr[hi - 1];
+  int pivot_idx = lo - 1;
+  for (int j = lo; j < hi; ++j) {
+    if (arr[j] < pivot) {
+      pivot_idx += 1;
+
+      temp = arr[j];
+      arr[j] = arr[pivot_idx];
+      arr[pivot_idx] = temp;
+    }
+  }
+
+  pivot_idx += 1;
+  temp = arr[hi - 1];
+  arr[hi - 1] = arr[pivot_idx];
+  arr[pivot_idx] = temp;
+
+  // Recursive call
+  local_quicksort(arr, lo, pivot_idx);
+  local_quicksort(arr, pivot_idx + 1, hi);
+}
+
+char *string_of_list(int *arr, int len) {
+  char *buffer = malloc(1000);
+  int offset = 0; // Keep track of the current position in the buffer
+  for (int i = 0; i < len; i++) {
+    offset += sprintf(buffer + offset, "%d", arr[i]);
+    if (i < len - 1) {
+      // Add a separator (e.g., comma or space) if it's not the last element
+      offset += sprintf(buffer + offset, " ");
+    }
+  }
+
+  return buffer;
+}
\ No newline at end of file