From f6d3090f7fa76eb8e0dbe060b8490cb49c001c39 Mon Sep 17 00:00:00 2001
From: nasr <nsrddyn@gmail.com>
Date: Mon, 5 Oct 2026 22:02:56 +0200
Subject: init: base

---
 source/base/base_arena.cpp | 165 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 165 insertions(+)
 create mode 100644 source/base/base_arena.cpp

(limited to 'source/base/base_arena.cpp')

diff --git a/source/base/base_arena.cpp b/source/base/base_arena.cpp
new file mode 100644
index 0000000..b4235e6
--- /dev/null
+++ b/source/base/base_arena.cpp
@@ -0,0 +1,165 @@
+#if PLATFORM_UNIX
+
+internal MemArena *
+unix_arena_create(u64 capacity)
+{
+    MemArena *arena = (MemArena *)mmap(
+                                       /* kernel decides where to throw the arena */
+                                       NULL,
+                                       capacity + sizeof(MemArena),
+                                       PROT_READ | PROT_WRITE,
+                                       MAP_SHARED | MAP_ANONYMOUS,
+                                       -1,
+                                       0);
+
+    if(arena == MAP_FAILED) {
+        return NULL;
+    }
+
+    arena->capacity          = capacity;
+    arena->base_position     = (u8 *)arena + sizeof(MemArena);
+    arena->current_position  = 0;
+    arena->previous_position = 0;
+
+    return arena;
+}
+
+internal void
+unix_arena_destroy(MemArena *arena)
+{
+    if(!arena) {
+        return;
+    }
+
+    munmap(arena, arena->capacity + sizeof(MemArena));
+}
+
+#elif PLATFORM_WINDOWS
+
+internal MemArena *
+win32_arena_create(u64 capacity)
+{
+    MemArena *arena = (MemArena *)VirtualAlloc(NULL,
+                                               capacity + sizeof(MemArena),
+                                               MEM_COMMIT | MEM_RESERVE,
+                                               PAGE_READWRITE);
+    if(!arena) {
+        return NULL;
+    }
+
+    arena->capacity          = capacity;
+    arena->base_position     = (u8 *)arena + sizeof(MemArena);
+    arena->current_position  = 0;
+    arena->previous_position = 0;
+    return arena;
+}
+
+internal void
+win32_arena_destroy(MemArena *arena)
+{
+    if(!arena) {
+        return;
+    }
+
+    VirtualFree(arena, 0, MEM_RELEASE);
+    return;
+}
+
+#endif
+
+internal void *
+arena_alloc(MemArena *arena, u64 size, b32 zero)
+{
+    Assert(arena);
+
+    u64 aligned = Align(arena->current_position, arena_align);
+    u64 new_pos = aligned + size;
+
+    AssertLog((new_pos <= arena->capacity), "max arena capacity reached\n");
+
+
+    void *out = arena->base_position + aligned;
+
+    arena->previous_position = arena->current_position;
+    arena->current_position  = aligned + size;
+
+    if(zero) {
+        MemSetZero(out, size);
+    }
+
+    return out;
+}
+
+internal void
+arena_pop(MemArena *arena, u64 size)
+{
+    size = Min(size, arena->current_position);
+    arena->current_position -= size;
+}
+
+internal void
+arena_pop_to(MemArena *arena, u64 pos)
+{
+    u64 size = pos < arena->current_position ? arena->current_position - pos : 0;
+    arena_pop(arena, size);
+}
+
+internal void
+arena_clear(MemArena *arena)
+{
+    arena->current_position = 0;
+}
+
+internal MemArena *
+arena_resize_block_align(MemArena *arena, void *old_memory, u64 new_size, u64 old_size, umm alignment)
+{
+    u8 *old_mem = (u8 *)old_memory;
+
+    if(is_pow(alignment)) {
+        arena->current_position = Align(arena->current_position, alignment);
+    }
+
+    if(old_memory == NULL || old_size == 0) {
+        return (MemArena *)arena_alloc(arena, new_size, 0);
+    } else if((old_mem >= arena->base_position && old_mem < arena->base_position + arena->current_position)) { // NOTE: does not find it self after the current position
+        if((arena->base_position + arena->previous_position) == old_memory) {
+            arena->current_position = arena->previous_position + new_size;
+            if(new_size > old_size) {
+                MemSet(&arena->current_position, new_size - old_size);
+            }
+
+            return (MemArena *)old_memory;
+        } else {
+            void *new_memory = arena_alloc(arena, new_size, 0);
+            umm   copy_size  = old_size < new_size ? old_size : new_size;
+            memmove(new_memory, old_mem, copy_size);
+        }
+    } else {
+        AssertLog(false, "Failed to resize memory.\n");
+    }
+
+    return NULL;
+}
+
+internal MemArena *
+arena_resize_block(MemArena *arena, void *old_memory, u64 new_size, u64 old_size)
+{
+    return arena_resize_block_align(arena, old_memory, new_size, old_size, arena_align);
+}
+
+internal ScratchArena
+scratch_start(MemArena *arena)
+{
+    ScratchArena scratch;
+    scratch.arena          = arena;
+    scratch.start_position = arena->current_position;
+
+    return scratch;
+}
+
+internal void
+scratch_end(ScratchArena *scratch)
+{
+    scratch->arena->current_position = scratch->start_position;
+}
+
-- 
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