From 4cabd4fbed3201a428fa9978e6e3e0a5bdb74100 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nils=20O=2E=20Sel=C3=A5sdal?= <nos@utel.tech>
Date: Thu, 4 Jun 2026 16:20:59 +0200
Subject: [PATCH] Start arena

---
 src/arena.c     | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/arena.h     | 34 ++++++++++++++++++++++
 src/base_core.h |  2 +-
 3 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 src/arena.c
 create mode 100644 src/arena.h

diff --git a/src/arena.c b/src/arena.c
new file mode 100644
index 0000000..3fdb9d3
--- /dev/null
+++ b/src/arena.c
@@ -0,0 +1,76 @@
+#include "arena.h"
+#include "base_core.h"
+#include <stdlib.h>
+//
+//note(nos) Move to platrofm layer
+static void *memory_allocate(size_t sz)
+{
+    return malloc(sz);
+}
+
+static void memory_release(void *mem)
+{
+    free(mem);
+}
+
+Arena *arena_alloc_(const ArenaParams *params)
+{
+    // Note: only backend now is malloc
+    Assert(params.size > ARENA_HEADER_SZ);
+    void *base = memory_allocate(params->size);
+    Assert(base != NULL);
+
+    Arena *arena = (Arena *)base;
+    arena->current  = arena;
+    arena->size     = params->size;
+    arena->pos      = ARENA_HEADER_SZ;
+    arena->prev     = NULL;
+
+    return arena;
+}
+
+
+void arena_free(Arena *arena)
+{
+    Arena *it = arena->current;
+    Arena *prev = NULL;
+
+    while (it != NULL) {
+        prev = it->prev;
+        memory_release(it);
+        it = prev;
+    }
+}
+
+
+
+void *arena_push(Arena *arena, U32 size, U32 align)
+{
+    Arena *current = arena->current;
+    U32 start_pos = AlignUpPow2(arena->pos, align);
+    U32 available = current->size - start_pos;
+
+    if (available > size) {
+
+        U8 *mem = &current->base[start_pos];
+        arena->pos = start_pos + size;
+        return mem;
+
+    } else {
+        // Note: We could hunt for a previous arena that still have room
+        U32 new_size = current->size;
+        if (new_size < size) {
+            new_size = size;
+        }
+
+        ArenaParams new_params  = {};
+        new_params.flags = current->flags;
+        new_params.size = size + ARENA_HEADER_SZ;
+        Arena *new_arena = arena_alloc_(&new_params);
+
+        new_arena->prev = current;
+        current->current = new_arena;
+        current = new_arena;
+
+    }
+}
diff --git a/src/arena.h b/src/arena.h
new file mode 100644
index 0000000..46a5231
--- /dev/null
+++ b/src/arena.h
@@ -0,0 +1,34 @@
+#pragma once
+#include "base_core.h"
+
+typedef U32 ArenaFlags;
+
+typedef struct ArenaParams ArenaParams;
+enum {
+    ArenaFlag_UseMalloc = (1 << 0),
+};
+struct ArenaParams {
+    U32 size;
+    ArenaFlags flags; // No flags defined yet
+};
+
+typedef struct Arena Arena;
+struct Arena {
+    Arena *current;
+    U8 *base;
+    U32 size;
+    U32 pos;
+    ArenaFlags flags;
+    Arena *prev;
+};
+
+StaticAssert(sizeof(Arena) <= 64);
+#define ARENA_HEADER_SZ 64
+
+
+INLINE U32 arena_available(const Arena *arena)
+{
+    return arena->size - arena->pos;
+}
+
+
diff --git a/src/base_core.h b/src/base_core.h
index a23e59d..40540a4 100644
--- a/src/base_core.h
+++ b/src/base_core.h
@@ -17,7 +17,7 @@ typedef uint64_t    U64;
 typedef float       F32;
 typedef double      F64;
 #if defined(__FLT128_MANT_DIG__) || defined(__FLOAT128__)
-typedef _Float128 F128;
+typedef __float128 F128;
 #endif
 #ifdef __SIZEOF_INT128__
 typedef __int128          S128;