From c75ca1999e76da939faac9524d5b4552d579c2c5 Mon Sep 17 00:00:00 2001
From: Nathan Giddings <nathang567@gmail.com>
Date: Sat, 1 Aug 2020 16:12:55 -0500
Subject: [PATCH] Wrote priority queue for processes

---
 src/process.hpp      | 23 ++++++++++++++++
 src/processqueue.cpp | 62 ++++++++++++++++++++++++++++++++++++++++++++
 src/processqueue.hpp | 35 +++++++++++++++++++++++++
 3 files changed, 120 insertions(+)
 create mode 100644 src/process.hpp
 create mode 100644 src/processqueue.cpp
 create mode 100644 src/processqueue.hpp

diff --git a/src/process.hpp b/src/process.hpp
new file mode 100644
index 0000000..68d6133
--- /dev/null
+++ b/src/process.hpp
@@ -0,0 +1,23 @@
+#ifndef PROCESS_H
+#define PROCESS_H
+
+#include <stddef.h>
+
+namespace kernel
+{
+
+class Process
+{
+public:
+
+    Process();
+
+    size_t priority;
+
+    void* stack;
+
+};
+
+};
+
+#endif
\ No newline at end of file
diff --git a/src/processqueue.cpp b/src/processqueue.cpp
new file mode 100644
index 0000000..4a9b929
--- /dev/null
+++ b/src/processqueue.cpp
@@ -0,0 +1,62 @@
+#include "processqueue.hpp"
+
+kernel::ProcessQueue::ProcessQueue(Process** array)
+{
+    m_array = array;
+    m_size = 0;
+}
+
+kernel::Process* kernel::ProcessQueue::extractMin()
+{
+    if(m_size == 0)
+        return NULL;
+    m_size--;
+    Process* p = m_array[0];
+    m_array[0] = m_array[m_size];
+    heapify(0);
+}
+
+void kernel::ProcessQueue::insert(Process* n)
+{
+    size_t i = m_size;
+    m_size++;
+    for(; i > 0 && m_array[(i - 1) / 2]->priority > n->priority; i = (i - 1) / 2)
+	{
+		m_array[i] = m_array[(i - 1) / 2];
+	}
+    m_array[i] = n;
+}
+
+void kernel::ProcessQueue::remove(Process* n)
+{
+    for(size_t i = 0; i < m_size; i++)
+    {
+        if(m_array[i] == n)
+        {
+            m_size--;
+            m_array[i] = m_array[m_size];
+            heapify(i);
+            break;
+        }
+    }
+}
+
+void kernel::ProcessQueue::heapify(size_t i)
+{
+    if(i * 2 + 1 >= m_size)
+			return;
+    if (m_array[i]->priority >= m_array[i * 2 + 1]->priority && m_array[i * 2 + 1]->priority <= m_array[i * 2 + 2]->priority)
+    {
+        Process* buffer = m_array[i];
+        m_array[i] = m_array[i * 2 + 1];
+        m_array[i * 2 + 1] = buffer;
+        heapify(i * 2 + 1);
+    }
+    else if (m_array[i]->priority >= m_array[i * 2 + 2]->priority && m_array[i * 2 + 2]->priority <= m_array[i * 2 + 1]->priority)
+    {
+        Process* buffer = m_array[i];
+        m_array[i] = m_array[i * 2 + 2];
+        m_array[i * 2 + 2] = buffer;
+        heapify(i * 2 + 2);
+    }
+}
\ No newline at end of file
diff --git a/src/processqueue.hpp b/src/processqueue.hpp
new file mode 100644
index 0000000..64b3f91
--- /dev/null
+++ b/src/processqueue.hpp
@@ -0,0 +1,35 @@
+#ifndef HEAP_H
+#define HEAP_H
+
+#include <stddef.h>
+
+#include "process.hpp"
+
+namespace kernel
+{
+
+class ProcessQueue
+{
+public:
+
+    ProcessQueue(Process** array);
+
+    Process* extractMin();
+
+    void insert(Process* n);
+
+    void remove(Process* n);
+
+private:
+
+    void heapify(size_t index);
+
+    Process** m_array;
+
+    size_t m_size;
+
+};
+
+}
+
+#endif
\ No newline at end of file