1 files changed, 113 insertions, 0 deletions
diff --git a/code/amr_memory.c b/code/amr_memory.c
new file mode 100644
index 0000000..f92f14a
--- /dev/null
+++ b/code/amr_memory.c
@@ -0,0 +1,113 @@
+#include "amr_memory.h"
+
+bool amr_IsPowerOfTwo(uintptr_t x)
+{
+  return (x & (x-1)) == 0;
+}
+
+uintptr_t amr_AlignForward(uintptr_t ptr, size_t align)
+{
+  uintptr_t p, a, modulo;
+
+  assert(amr_IsPowerOfTwo(align));
+
+  p = ptr;
+  a = (uintptr_t)align;
+  modulo = p & (a-1);
+
+  if (modulo != 0)
+  {
+    p += a - modulo;
+  }
+  return p;
+}
+
+void *amr_ArenaAllocAlign(amr_DebugArena *Alloc, size_t Size, size_t Align)
+{
+  uintptr_t CurrOffset = (uintptr_t)Alloc->Buffer + (uintptr_t)Alloc->CurrOffset;
+  uintptr_t AlignedOffset = amr_AlignForward(CurrOffset, Align);
+  AlignedOffset -= (uintptr_t)(Alloc->Buffer);
+
+  if (AlignedOffset + Size < Alloc->Size)
+  {
+    void *Ptr = &Alloc->Buffer[AlignedOffset];
+    Alloc->PrevOffset = AlignedOffset;
+    Alloc->CurrOffset = AlignedOffset + Size;
+
+    PlatformZeroMemory(Ptr, Size);
+    return Ptr;
+  }
+  return NULL;
+}
+
+void amr_ArenaInit(amr_DebugArena *Alloc, void* BackingBuffer, size_t Size)
+{
+  Alloc->Buffer = (u8 *)BackingBuffer;
+  Alloc->Size = Size;
+  Alloc->CurrOffset = 0;
+  Alloc->PrevOffset = 0;
+}
+
+void *amr_ArenaAlloc(amr_DebugArena *Alloc, size_t Size)
+{
+  return amr_ArenaAllocAlign(Alloc, Size, DEFAULT_ALIGNMENT);
+}
+
+void amr_ArenaFree(amr_DebugArena *Alloc, void *Ptr)
+{
+  // @note: Arenas do not support freeing memory
+  // this is here to let me know I have not forgotten to implement it
+  return;
+}
+
+void *amr_ArenaResizeAlign(amr_DebugArena *Alloc, void *OldMem, size_t OldSize,
+                        size_t NewSize, size_t Align)
+{
+  assert(amr_IsPowerOfTwo(Align));
+  if (OldMem == NULL || OldSize == 0)
+  {
+    return amr_ArenaAllocAlign(Alloc, NewSize, Align);
+  }
+  else if (Alloc->Buffer < OldMem && OldMem < Alloc->Buffer + Alloc->Size)
+  {
+    // check if old_memory falls on prev_offset
+    if (Alloc->Buffer + Alloc->PrevOffset == OldMem)
+    {
+      // re-use prev_offset and resize from there
+      size_t _CurrOffset = Alloc->CurrOffset;
+      Alloc->CurrOffset = Alloc->PrevOffset + NewSize;
+      if (NewSize > OldSize)
+      {
+        PlatformZeroMemory(&Alloc->Buffer[_CurrOffset], NewSize - OldSize); 
+      }
+      return OldMem;
+    }
+    else
+    {
+      // generate new memory
+      // will have some fragmentation
+      void *NewMem = amr_ArenaAllocAlign(Alloc, NewSize, Align);
+      size_t CopySize = OldSize < NewSize ? OldSize : NewSize;
+
+      // copy old memory to new memory location
+      PlatformCopyMemory(NewMem, OldMem, CopySize);
+      return NewMem;
+    }
+  }
+  else
+  {
+    assert(0 && "Memory is out of bounds of the buffer in this arena");
+    return NULL;
+  }
+}
+
+void *amr_ArenaResize(amr_DebugArena *Alloc, void *OldMem, size_t OldSize, size_t NewSize)
+{
+  return amr_ArenaResizeAlign(Alloc, OldMem, OldSize, NewSize, DEFAULT_ALIGNMENT);
+}
+
+void amr_ArenaFreeAll(amr_DebugArena *Alloc)
+{
+  Alloc->CurrOffset = 0;
+  Alloc->PrevOffset = 0;
+}