Add makefile and restructure

src/arena.c

@@ -0,0 +1,60 @@
+
+
+#include "arena.h"
+#include "alloc_backend.h"
+
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+
+#define ARENA_SIZE ((size_t)(128*sysconf(_SC_PAGE_SIZE)))
+
+/*
+ * Allocates and returns new arena
+ */
+struct arena* arena_new()
+{
+    size_t size = ARENA_SIZE;
+
+    unsigned char *p = call_alloc_backend(size);
+
+    if (p == NULL)
+        return NULL;
+
+    struct arena a = {
+        .begin = p + sizeof(struct arena),
+        .next  = p + sizeof(struct arena),
+        .cap   = size
+    };
+
+    memcpy(p, &a, sizeof a);
+
+    return (struct arena*)p;
+}
+
+
+/*
+ * Frees all memory in arena
+ */
+void arena_reset(struct arena *a)
+{
+    a->next = a->begin;
+}
+
+
+/*
+ * Allocate new memory using arena
+ */
+void* arena_alloc(struct arena *a, size_t len)
+{
+    void *p = a->next;
+    a->next += len;
+
+    if (a->next - a->begin >= a->cap) {
+        errno = ENOMEM;
+        return NULL;
+    }
+
+    return p;
+}
+