From 6e1952eab0ee2eed5c105311df56e603857798c2 Mon Sep 17 00:00:00 2001
From: Matthew <matthew@sleepy.day>
Date: Sat, 27 Sep 2025 20:40:36 +1000
Subject: [PATCH] fix arena bugs

---
 alloc.d | 41 ++++++++++++++++++++++++++---------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/alloc.d b/alloc.d
index d48a589..c5d256d 100644
--- a/alloc.d
+++ b/alloc.d
@@ -24,13 +24,13 @@ struct ArenaPool
 {
 	u8* mem;
 	u64 pos;
+	u64 length;
 }
 
 struct Arena
 {
 	SLList!(ArenaPool) pools;
-	u64                pool_length;
-	u64                length;
+	u64                def_size;
 }
 
 struct TempArena
@@ -107,11 +107,10 @@ Arena
 CreateArena(u64 size)
 {
 	Arena arena = { 
-		length: size,
-		pool_length: size - Node!(ArenaPool).sizeof,
+		def_size: size,
 	};
 
-	AddArenaPool(&arena);
+	AddArenaPool(&arena, size);
 
 	return arena;
 }
@@ -182,14 +181,15 @@ Alloc(T)(TempArena* t)
 }
 
 void
-AddArenaPool(Arena* arena)
+AddArenaPool(Arena* arena, u64 size)
 {
-	u8* mem = cast(u8*)MemAlloc(arena.length);
+	u8* mem = Alloc!(u8)(size + Node!(ArenaPool).sizeof).ptr;
 
 	Node!(ArenaPool)* node = cast(Node!(ArenaPool)*)mem;
 
 	node.value.mem = (cast(u8*)mem) + Node!(ArenaPool).sizeof;
 	node.value.pos = 0;
+	node.value.length = size;
 
 	assert(node.value.mem != null, "Unable to allocate memory for arena");
 
@@ -229,8 +229,6 @@ Alloc(T)(Arena* arena)
 void* 
 AllocAlign(Arena* arena, u64 size, u64 alignment)
 {
-	assert(size <= arena.pool_length, "Unable to allocate memory within arena size");
-
 	void* ptr = null;
 
 	uintptr mem_pos, current, offset;
@@ -239,7 +237,12 @@ AllocAlign(Arena* arena, u64 size, u64 alignment)
 	{
 		if(node == null)
 		{
-			AddArenaPool(arena);
+			if(size > arena.def_size)
+			{
+				size += arena.def_size;
+			}
+
+			AddArenaPool(arena, Max(size, arena.def_size));
 			node = arena.pools.first;
 		}
 
@@ -247,7 +250,7 @@ AllocAlign(Arena* arena, u64 size, u64 alignment)
 		current = mem_pos + node.value.pos;
 		offset = AlignPow2(current, alignment) - mem_pos;
 
-		if(offset+size <= arena.pool_length)
+		if(offset+size <= node.value.length)
 		{
 			break;
 		}
@@ -278,7 +281,7 @@ Free(Arena* arena)
 	Node!(ArenaPool)* node = arena.pools.first;
 	while (node != null)
 	{
-		MemFree(node.value.mem, arena.length);
+		Free(node);
 		node = node.next;
 	}
 }
@@ -329,9 +332,17 @@ ScratchAllocCopy(T)(T[] target)
 
 unittest
 {
-	u64[5] arr = [1, 2, 3, 4, 5];
+	{
+		u64[5] arr = [1, 2, 3, 4, 5];
 
-	u64[] copy = AllocCopy!(u64)(arr);
+		u64[] copy = AllocCopy!(u64)(arr);
 
-	assert(arr == copy);
+		assert(arr == copy);
+	}
+
+	{
+		Arena a = CreateArena(64);
+
+		u64[] arr = Alloc!(u64)(&a, 128);
+	}
 }