From 2f246bdf592d91c643bdc8c9c138f995c67f6ae7 Mon Sep 17 00:00:00 2001
From: rhuibertsjr <rhuibertsjr@gmail.com>
Date: Fri, 26 Apr 2024 17:00:32 +0200
Subject: [PATCH] Added: growable arenas on allocation

---
 src/arena.c | 40 +++++++++++++++++++++++++++++++++++++++-
 src/arena.h |  2 +-
 src/base.h  |  4 ++++
 src/main.c  |  4 ++++
 4 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/src/arena.c b/src/arena.c
index 3f910ea..b313863 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -10,10 +10,11 @@ arena_initialize(u64 size, b8 growable)
 
     result = (Arena*) backing_buffer;
     result->backing_buffer = backing_buffer;
+    result->current = result;
 
     // rhjr: immutable arena header
     result->base_pos = sizeof(Arena);
-    result->commit_pos = sizeof(Arena);
+    result->offset = sizeof(Arena);
 
     result->growable = growable;
     result->size = size;
@@ -35,6 +36,43 @@ arena_initialize_default()
 internal void *
 arena_allocate(Arena *arena, u64 size)
 {
+  Arena *current = arena->current;
+  u64    pos_mem = current->offset;
+  u64    pos_new = current->offset + size;
+
+  if (current->size < pos_new && current->growable)
+  {
+    Arena *new_memory_bock;
+
+    if (size > ARENA_DEFAULT_RESERVE_SIZE)
+    {
+      // rhjr: TODO add support for allocations larger then a single page, in a
+      //       single allocation call.
+    }
+    else
+    {
+      new_memory_bock = arena_initialize_default();
+
+      if (new_memory_bock)
+      {
+	sll_stack_push(arena->current, new_memory_bock, prev);
+
+	current = new_memory_bock;
+	pos_mem = current->offset;
+	pos_new = current->offset + size;
+      }
+
+    }
+
+  }
+
+  void *memory = (void*)((u64) current->backing_buffer + pos_mem);
+  arena->offset = pos_new;
+
+  platform_memory_commit(memory, size);
+  memset(memory, 0, size);
+
+  return memory;
 }
 
 internal void
diff --git a/src/arena.h b/src/arena.h
index 103a367..547b837 100644
--- a/src/arena.h
+++ b/src/arena.h
@@ -13,7 +13,7 @@ struct Arena {
   struct Arena *prev;
   u64 *backing_buffer;
   u64 base_pos;
-  u64 commit_pos;
+  u64 offset;
   u64 size;
   b8 growable;
 };
diff --git a/src/base.h b/src/base.h
index e7d93f9..db6336e 100644
--- a/src/base.h
+++ b/src/base.h
@@ -33,6 +33,10 @@ typedef uint8_t  b64;
 #define ASSERT(c) STATEMENT( if (!(c)){ (*(volatile int*)0 = 0); } )
 #define STATIC_ASSERT(c,l) typedef u8 Glue(l,__LINE__) [(c)?1:-1]
 
+//= rhjr: linkedlist helpers
+
+#define sll_stack_push(f,n,next) ((n)->next=(f), (f)=(n))
+
 //= rhjr: memory helpers
 
 #define memory_zero(s,z)       memset((s), 0, (z))
diff --git a/src/main.c b/src/main.c
index 0d8fb62..b54f935 100644
--- a/src/main.c
+++ b/src/main.c
@@ -9,5 +9,9 @@ int
 main(void)
 {
   Arena *arena = arena_initialize_default();
+  u64* ptr1 = arena_allocate(arena, KB(3));
+  u64* ptr2 = arena_allocate(arena, KB(2));
+
+  arena_release(arena);
   return 0;
 }