main.c

@@ -1,15 +1,110 @@
 #include <stddef.h>
+#include <stdio.h>
+#include <unistd.h>
 
-void* malloc(unsigned long size)
+#define ALIGN4(s) (((((s)-1)>>2)<<2)+4)
+#define BLOCK_SIZE sizeof(struct block)
+
+struct block
 {
-	return NULL;
+	size_t size;
+	struct block* next;
+	int free;
+};
+
+struct block* freeList = NULL;
+
+struct block* extend_heap(struct block* last, size_t s)
+{
+	struct block* b = sbrk(0);
+
+	if (sbrk(BLOCK_SIZE + s) == (void*)-1)
+		return NULL;
+
+	b->size = s;
+	b->next = NULL;
+	b->free = 0;
+
+	if (last)
+		last->next = b;
+
+	return b;
+}
+
+struct block* find_first(size_t s)
+{
+	struct block* current = freeList;
+	while (current && (!current->free || current->size < s))
+		current = current->next;
+
+	return current;
+}
+
+struct block* find_last()
+{
+	struct block* current = freeList;
+	while (current && current->next)
+		current = freeList->next;
+
+	return current;
+}
+
+void* malloc(size_t size)
+{
+	struct block* b;
+
+	size_t alignedSize = ALIGN4(size);
+
+	if (freeList)
+	{
+		b = find_first(alignedSize);
+		if (!b)
+			b = extend_heap(find_last(), alignedSize);
+	}
+	else
+	{
+		b = extend_heap(NULL, alignedSize);
+		if (!b)
+			return NULL;
+
+		freeList = b;
+	}
+
+	return (char*)b + BLOCK_SIZE;
 }
 
 void free(void* ptr)
 {
+	if (!ptr)
+		return;
+
+	struct block* b = (struct block*)((char*)ptr - BLOCK_SIZE);
+	b->free = 1;
+
+	struct block* link = b->next;
+	while (b->next && b->next->free)
+	{
+		b->size += BLOCK_SIZE + b->next->size;
+		b->next = link->next;
+	}
+
+	if (!b->next)
+		brk(b);
 }
 
-int main(void)
+int main()
 {
+	int* a = (int*)malloc(sizeof(int));
+	int* b = (int*)malloc(sizeof(int));
+
+	*a = 5;
+	*b = 12;
+
+	printf("Test 1: %i\n", *a);
+	printf("Test 2: %i", *b);
+
+	free(b);
+	free(a);
+
 	return 0;
 }