Dqn/Base/dn_base_mem.cpp

#define DN_BASE_MEM_CPP

static DN_ArenaBlock *DN_Arena_BlockInitFromMemFuncs_(DN_U64 reserve, DN_U64 commit, bool track_alloc, bool alloc_can_leak, DN_ArenaMemFuncs mem_funcs)
{
  DN_ArenaBlock *result = nullptr;
  switch (mem_funcs.type) {
    case DN_ArenaMemFuncType_Nil:
      break;

    case DN_ArenaMemFuncType_Basic: {
      DN_AssertF(reserve > DN_ARENA_HEADER_SIZE, "%I64u > %I64u", reserve, DN_ARENA_HEADER_SIZE);
      result = DN_CAST(DN_ArenaBlock *) mem_funcs.basic_alloc(reserve);
      if (!result)
        return result;

      result->used    = DN_ARENA_HEADER_SIZE;
      result->commit  = reserve;
      result->reserve = reserve;
    } break;

    case DN_ArenaMemFuncType_VMem: {
      DN_AssertF(mem_funcs.vmem_page_size, "Page size must be set to a non-zero, power of two value");
      DN_Assert(DN_IsPowerOfTwo(mem_funcs.vmem_page_size));

      DN_USize const page_size    = mem_funcs.vmem_page_size;
      DN_U64         real_reserve = reserve ? reserve : DN_ARENA_RESERVE_SIZE;
      DN_U64         real_commit  = commit ? commit   : DN_ARENA_COMMIT_SIZE;
      real_reserve                = DN_AlignUpPowerOfTwo(real_reserve, page_size);
      real_commit                 = DN_Min(DN_AlignUpPowerOfTwo(real_commit, page_size), real_reserve);
      DN_AssertF(DN_ARENA_HEADER_SIZE < real_commit && real_commit <= real_reserve, "%I64u < %I64u <= %I64u", DN_ARENA_HEADER_SIZE, real_commit, real_reserve);

      DN_MemCommit mem_commit = real_reserve == real_commit ? DN_MemCommit_Yes : DN_MemCommit_No;
      result                    = DN_CAST(DN_ArenaBlock *) mem_funcs.vmem_reserve(real_reserve, mem_commit, DN_MemPage_ReadWrite);
      if (!result)
        return result;

      if (mem_commit == DN_MemCommit_No && !mem_funcs.vmem_commit(result, real_commit, DN_MemPage_ReadWrite)) {
        mem_funcs.vmem_release(result, real_reserve);
        return result;
      }

      result->used    = DN_ARENA_HEADER_SIZE;
      result->commit  = real_commit;
      result->reserve = real_reserve;
    } break;
  }

  if (track_alloc && result)
    DN_Debug_TrackAlloc(result, result->reserve, alloc_can_leak);

  return result;
}

static DN_ArenaBlock *DN_Arena_BlockInitFlagsFromMemFuncs_(DN_U64 reserve, DN_U64 commit, DN_ArenaFlags flags, DN_ArenaMemFuncs mem_funcs)
{
  bool           track_alloc    = (flags & DN_ArenaFlags_NoAllocTrack) == 0;
  bool           alloc_can_leak = flags & DN_ArenaFlags_AllocCanLeak;
  DN_ArenaBlock *result         = DN_Arena_BlockInitFromMemFuncs_(reserve, commit, track_alloc, alloc_can_leak, mem_funcs);
  if (result && ((flags & DN_ArenaFlags_NoPoison) == 0))
    DN_ASAN_PoisonMemoryRegion(DN_CAST(char *) result + DN_ARENA_HEADER_SIZE, result->commit - DN_ARENA_HEADER_SIZE);
  return result;
}

static void DN_Arena_UpdateStatsOnNewBlock_(DN_Arena *arena, DN_ArenaBlock const *block)
{
  DN_Assert(arena);
  if (block) {
    arena->stats.info.used    += block->used;
    arena->stats.info.commit  += block->commit;
    arena->stats.info.reserve += block->reserve;
    arena->stats.info.blocks  += 1;

    arena->stats.hwm.used    = DN_Max(arena->stats.hwm.used,    arena->stats.info.used);
    arena->stats.hwm.commit  = DN_Max(arena->stats.hwm.commit,  arena->stats.info.commit);
    arena->stats.hwm.reserve = DN_Max(arena->stats.hwm.reserve, arena->stats.info.reserve);
    arena->stats.hwm.blocks  = DN_Max(arena->stats.hwm.blocks,  arena->stats.info.blocks);
  }
}

DN_API DN_Arena DN_Arena_InitFromBuffer(void *buffer, DN_USize size, DN_ArenaFlags flags)
{
  DN_Assert(buffer);
  DN_AssertF(DN_ARENA_HEADER_SIZE < size, "Buffer (%zu bytes) too small, need atleast %zu bytes to store arena metadata", size, DN_ARENA_HEADER_SIZE);
  DN_AssertF(DN_IsPowerOfTwo(size), "Buffer (%zu bytes) must be a power-of-two", size);

  // NOTE: Init block
  DN_ArenaBlock *block = DN_CAST(DN_ArenaBlock *) buffer;
  block->commit        = size;
  block->reserve       = size;
  block->used          = DN_ARENA_HEADER_SIZE;
  if (block && ((flags & DN_ArenaFlags_NoPoison) == 0))
    DN_ASAN_PoisonMemoryRegion(DN_CAST(char *) block + DN_ARENA_HEADER_SIZE, block->commit - DN_ARENA_HEADER_SIZE);

  DN_Arena result = {};
  result.flags    = flags | DN_ArenaFlags_NoGrow | DN_ArenaFlags_NoAllocTrack | DN_ArenaFlags_AllocCanLeak | DN_ArenaFlags_UserBuffer;
  result.curr     = block;
  DN_Arena_UpdateStatsOnNewBlock_(&result, result.curr);
  return result;
}

DN_API DN_Arena DN_Arena_InitFromMemFuncs(DN_U64 reserve, DN_U64 commit, DN_ArenaFlags flags, DN_ArenaMemFuncs mem_funcs)
{
  DN_Arena result   = {};
  result.flags      = flags;
  result.mem_funcs  = mem_funcs;
  result.flags     |= DN_ArenaFlags_MemFuncs;
  result.curr       = DN_Arena_BlockInitFlagsFromMemFuncs_(reserve, commit, flags, mem_funcs);
  DN_Arena_UpdateStatsOnNewBlock_(&result, result.curr);
  return result;
}

static void DN_Arena_BlockDeinit_(DN_Arena const *arena, DN_ArenaBlock *block)
{
  DN_USize release_size = block->reserve;
  if (DN_Bit_IsNotSet(arena->flags, DN_ArenaFlags_NoAllocTrack))
    DN_Debug_TrackDealloc(block);
  DN_ASAN_UnpoisonMemoryRegion(block, block->commit);
  if (arena->flags & DN_ArenaFlags_MemFuncs) {
    if (arena->mem_funcs.type == DN_ArenaMemFuncType_Basic)
      arena->mem_funcs.basic_dealloc(block);
    else
      arena->mem_funcs.vmem_release(block, release_size);
  }
}

DN_API void DN_Arena_Deinit(DN_Arena *arena)
{
  for (DN_ArenaBlock *block = arena ? arena->curr : nullptr; block;) {
    DN_ArenaBlock *block_to_free = block;
    block                        = block->prev;
    DN_Arena_BlockDeinit_(arena, block_to_free);
  }
  if (arena)
    *arena = {};
}

DN_API bool DN_Arena_CommitTo(DN_Arena *arena, DN_U64 pos)
{
  if (!arena || !arena->curr)
    return false;

  DN_ArenaBlock *curr = arena->curr;
  if (pos <= curr->commit)
    return true;

  DN_U64 real_pos = pos;
  if (!DN_Check(pos <= curr->reserve))
    real_pos = curr->reserve;

  DN_Assert(arena->mem_funcs.vmem_page_size);
  DN_USize end_commit  = DN_AlignUpPowerOfTwo(real_pos, arena->mem_funcs.vmem_page_size);
  DN_USize commit_size = end_commit - curr->commit;
  char    *commit_ptr  = DN_CAST(char *) curr + curr->commit;
  if (!arena->mem_funcs.vmem_commit(commit_ptr, commit_size, DN_MemPage_ReadWrite))
    return false;

  bool poison = DN_ASAN_POISON && ((arena->flags & DN_ArenaFlags_NoPoison) == 0);
  if (poison)
    DN_ASAN_PoisonMemoryRegion(commit_ptr, commit_size);

  curr->commit = end_commit;
  return true;
}

DN_API bool DN_Arena_Commit(DN_Arena *arena, DN_U64 size)
{
  if (!arena || !arena->curr)
    return false;
  DN_U64 pos    = DN_Min(arena->curr->reserve, arena->curr->commit + size);
  bool   result = DN_Arena_CommitTo(arena, pos);
  return result;
}

DN_API bool DN_Arena_Grow(DN_Arena *arena, DN_U64 reserve, DN_U64 commit)
{
  if (arena->flags & (DN_ArenaFlags_NoGrow | DN_ArenaFlags_UserBuffer))
    return false;

  bool result = false;
  DN_ArenaBlock *new_block = DN_Arena_BlockInitFlagsFromMemFuncs_(reserve, commit, arena->flags, arena->mem_funcs);
  if (new_block) {
    result                      = true;
    new_block->prev             = arena->curr;
    arena->curr                 = new_block;
    new_block->reserve_sum      = new_block->prev->reserve_sum + new_block->prev->reserve;
    DN_Arena_UpdateStatsOnNewBlock_(arena, arena->curr);
  }
  return result;
}

DN_API void *DN_Arena_Alloc(DN_Arena *arena, DN_U64 size, uint8_t align, DN_ZeroMem zero_mem)
{
  if (!arena)
    return nullptr;

  if (!arena->curr) {
    arena->curr = DN_Arena_BlockInitFlagsFromMemFuncs_(DN_ARENA_RESERVE_SIZE, DN_ARENA_COMMIT_SIZE, arena->flags, arena->mem_funcs);
    DN_Arena_UpdateStatsOnNewBlock_(arena, arena->curr);
  }

  if (!arena->curr)
    return nullptr;

  try_alloc_again:
  DN_ArenaBlock *curr       = arena->curr;
  bool           poison     = DN_ASAN_POISON && ((arena->flags & DN_ArenaFlags_NoPoison) == 0);
  uint8_t        real_align = poison ? DN_Max(align, DN_ASAN_POISON_ALIGNMENT) : align;
  DN_U64         offset_pos = DN_AlignUpPowerOfTwo(curr->used, real_align) + (poison ? DN_ASAN_POISON_GUARD_SIZE : 0);
  DN_U64         end_pos    = offset_pos + size;
  DN_U64         alloc_size = end_pos - curr->used;

  if (end_pos > curr->reserve) {
    if (arena->flags & (DN_ArenaFlags_NoGrow | DN_ArenaFlags_UserBuffer))
      return nullptr;
    DN_USize new_reserve = DN_Max(DN_ARENA_HEADER_SIZE + alloc_size, DN_ARENA_RESERVE_SIZE);
    DN_USize new_commit  = DN_Max(DN_ARENA_HEADER_SIZE + alloc_size, DN_ARENA_COMMIT_SIZE);
    if (!DN_Arena_Grow(arena, new_reserve, new_commit))
      return nullptr;
    goto try_alloc_again;
  }

  DN_USize prev_arena_commit = curr->commit;
  if (end_pos > curr->commit) {
    DN_Assert(arena->mem_funcs.vmem_page_size);
    DN_Assert(arena->mem_funcs.type == DN_ArenaMemFuncType_VMem);
    DN_Assert((arena->flags & DN_ArenaFlags_UserBuffer) == 0);
    DN_USize end_commit  = DN_AlignUpPowerOfTwo(end_pos, arena->mem_funcs.vmem_page_size);
    DN_USize commit_size = end_commit - curr->commit;
    char    *commit_ptr  = DN_CAST(char *) curr + curr->commit;
    if (!arena->mem_funcs.vmem_commit(commit_ptr, commit_size, DN_MemPage_ReadWrite))
      return nullptr;
    if (poison)
      DN_ASAN_PoisonMemoryRegion(commit_ptr, commit_size);
    curr->commit              = end_commit;
    arena->stats.info.commit += commit_size;
    arena->stats.hwm.commit   = DN_Max(arena->stats.hwm.commit, arena->stats.info.commit);
  }

  void *result            = DN_CAST(char *) curr + offset_pos;
  curr->used             += alloc_size;
  arena->stats.info.used += alloc_size;
  arena->stats.hwm.used   = DN_Max(arena->stats.hwm.used, arena->stats.info.used);
  DN_ASAN_UnpoisonMemoryRegion(result, size);

  if (zero_mem == DN_ZeroMem_Yes) {
    DN_USize reused_bytes = DN_Min(prev_arena_commit - offset_pos, size);
    DN_Memset(result, 0, reused_bytes);
  }

  DN_Assert(arena->stats.hwm.used >= arena->stats.info.used);
  DN_Assert(arena->stats.hwm.commit >= arena->stats.info.commit);
  DN_Assert(arena->stats.hwm.reserve >= arena->stats.info.reserve);
  DN_Assert(arena->stats.hwm.blocks >= arena->stats.info.blocks);
  return result;
}

DN_API void *DN_Arena_AllocContiguous(DN_Arena *arena, DN_U64 size, uint8_t align, DN_ZeroMem zero_mem)
{
  DN_ArenaFlags prev_flags  = arena->flags;
  arena->flags             |= (DN_ArenaFlags_NoGrow | DN_ArenaFlags_NoPoison);
  void *memory              = DN_Arena_Alloc(arena, size, align, zero_mem);
  arena->flags              = prev_flags;
  return memory;
}

DN_API void *DN_Arena_Copy(DN_Arena *arena, void const *data, DN_U64 size, uint8_t align)
{
  if (!arena || !data || size == 0)
    return nullptr;
  void *result = DN_Arena_Alloc(arena, size, align, DN_ZeroMem_No);
  if (result)
    DN_Memcpy(result, data, size);
  return result;
}

DN_API void DN_Arena_PopTo(DN_Arena *arena, DN_U64 init_used)
{
  if (!arena || !arena->curr)
    return;
  DN_U64         used = DN_Max(DN_ARENA_HEADER_SIZE, init_used);
  DN_ArenaBlock *curr = arena->curr;
  while (curr->reserve_sum >= used) {
    DN_ArenaBlock *block_to_free = curr;
    arena->stats.info.used    -= block_to_free->used;
    arena->stats.info.commit  -= block_to_free->commit;
    arena->stats.info.reserve -= block_to_free->reserve;
    arena->stats.info.blocks  -= 1;
    if (arena->flags & DN_ArenaFlags_UserBuffer)
      break;
    curr = curr->prev;
    DN_Arena_BlockDeinit_(arena, block_to_free);
  }

  arena->stats.info.used -= curr->used;
  arena->curr          = curr;
  curr->used           = used - curr->reserve_sum;
  char    *poison_ptr  = (char *)curr + DN_AlignUpPowerOfTwo(curr->used, DN_ASAN_POISON_ALIGNMENT);
  DN_USize poison_size = ((char *)curr + curr->commit) - poison_ptr;
  DN_ASAN_PoisonMemoryRegion(poison_ptr, poison_size);
  arena->stats.info.used += curr->used;
}

DN_API void DN_Arena_Pop(DN_Arena *arena, DN_U64 amount)
{
  DN_ArenaBlock *curr     = arena->curr;
  DN_USize       used_sum = curr->reserve_sum + curr->used;
  if (!DN_Check(amount <= used_sum))
    amount = used_sum;
  DN_USize pop_to = used_sum - amount;
  DN_Arena_PopTo(arena, pop_to);
}

DN_API DN_U64 DN_Arena_Pos(DN_Arena const *arena)
{
  DN_U64 result = (arena && arena->curr) ? arena->curr->reserve_sum + arena->curr->used : 0;
  return result;
}

DN_API void DN_Arena_Clear(DN_Arena *arena)
{
  DN_Arena_PopTo(arena, 0);
}

DN_API bool DN_Arena_OwnsPtr(DN_Arena const *arena, void *ptr)
{
  bool      result   = false;
  uintptr_t uint_ptr = DN_CAST(uintptr_t) ptr;
  for (DN_ArenaBlock const *block = arena ? arena->curr : nullptr; !result && block; block = block->prev) {
    uintptr_t begin = DN_CAST(uintptr_t) block + DN_ARENA_HEADER_SIZE;
    uintptr_t end   = begin + block->reserve;
    result          = uint_ptr >= begin && uint_ptr <= end;
  }
  return result;
}

DN_API DN_ArenaStats DN_Arena_SumStatsArray(DN_ArenaStats const *array, DN_USize size)
{
  DN_ArenaStats result = {};
  DN_ForItSize(it, DN_ArenaStats const, array, size)
  {
    DN_ArenaStats stats  = *it.data;
    result.info.used    += stats.info.used;
    result.info.commit  += stats.info.commit;
    result.info.reserve += stats.info.reserve;
    result.info.blocks  += stats.info.blocks;

    result.hwm.used      = DN_Max(result.hwm.used, result.info.used);
    result.hwm.commit    = DN_Max(result.hwm.commit, result.info.commit);
    result.hwm.reserve   = DN_Max(result.hwm.reserve, result.info.reserve);
    result.hwm.blocks    = DN_Max(result.hwm.blocks, result.info.blocks);
  }
  return result;
}

DN_API DN_ArenaStats DN_Arena_SumStats(DN_ArenaStats lhs, DN_ArenaStats rhs)
{
  DN_ArenaStats array[] = {lhs, rhs};
  DN_ArenaStats result  = DN_Arena_SumStatsArray(array, DN_ArrayCountU(array));
  return result;
}

DN_API DN_ArenaStats DN_Arena_SumArenaArrayToStats(DN_Arena const *array, DN_USize size)
{
  DN_ArenaStats result = {};
  for (DN_USize index = 0; index < size; index++) {
    DN_Arena const *arena = array + index;
    result                = DN_Arena_SumStats(result, arena->stats);
  }
  return result;
}

DN_API DN_ArenaTempMem DN_Arena_TempMemBegin(DN_Arena *arena)
{
  DN_ArenaTempMem result = {};
  if (arena) {
    DN_ArenaBlock *curr = arena->curr;
    result              = {arena, curr ? curr->reserve_sum + curr->used : 0};
  }
  return result;
};

DN_API void DN_Arena_TempMemEnd(DN_ArenaTempMem mem)
{
  DN_Arena_PopTo(mem.arena, mem.used_sum);
};

DN_ArenaTempMemScope::DN_ArenaTempMemScope(DN_Arena *arena)
{
  mem = DN_Arena_TempMemBegin(arena);
}

DN_ArenaTempMemScope::~DN_ArenaTempMemScope()
{
  DN_Arena_TempMemEnd(mem);
}

// NOTE: DN_Pool ///////////////////////////////////////////////////////////////////////////////////
DN_API DN_Pool DN_Pool_Init(DN_Arena *arena, uint8_t align)
{
  DN_Pool result = {};
  if (arena) {
    result.arena = arena;
    result.align = align ? align : DN_POOL_DEFAULT_ALIGN;
  }
  return result;
}

DN_API bool DN_Pool_IsValid(DN_Pool const *pool)
{
  bool result = pool && pool->arena && pool->align;
  return result;
}

DN_API void *DN_Pool_Alloc(DN_Pool *pool, DN_USize size)
{
  void *result = nullptr;
  if (!DN_Pool_IsValid(pool))
    return result;

  DN_USize const required_size       = sizeof(DN_PoolSlot) + pool->align + size;
  DN_USize const size_to_slot_offset = 5; // __lzcnt64(32) e.g. DN_PoolSlotSize_32B
  DN_USize       slot_index          = 0;
  if (required_size > 32) {
    // NOTE: Round up if not PoT as the low bits are set.
    DN_USize dist_to_next_msb = DN_CountLeadingZerosU64(required_size) + 1;
    dist_to_next_msb -= DN_CAST(DN_USize)(!DN_IsPowerOfTwo(required_size));

    DN_USize const register_size = sizeof(DN_USize) * 8;
    DN_Assert(register_size >= dist_to_next_msb + size_to_slot_offset);
    slot_index = register_size - dist_to_next_msb - size_to_slot_offset;
  }

  if (!DN_CheckF(slot_index < DN_PoolSlotSize_Count, "Chunk pool does not support the requested allocation size"))
    return result;

  DN_USize slot_size_in_bytes = 1ULL << (slot_index + size_to_slot_offset);
  DN_Assert(required_size <= (slot_size_in_bytes << 0));
  DN_Assert(required_size >= (slot_size_in_bytes >> 1));

  DN_PoolSlot *slot = nullptr;
  if (pool->slots[slot_index]) {
    slot                    = pool->slots[slot_index];
    pool->slots[slot_index] = slot->next;
    DN_Memset(slot->data, 0, size);
    DN_Assert(DN_IsPowerOfTwoAligned(slot->data, pool->align));
  } else {
    void *bytes = DN_Arena_Alloc(pool->arena, slot_size_in_bytes, alignof(DN_PoolSlot), DN_ZeroMem_Yes);
    slot        = DN_CAST(DN_PoolSlot *) bytes;

    // NOTE: The raw pointer is round up to the next 'pool->align'-ed
    // address ensuring at least 1 byte of padding between the raw pointer
    // and the pointer given to the user and that the user pointer is
    // aligned to the pool's alignment.
    //
    // This allows us to smuggle 1 byte behind the user pointer that has
    // the offset to the original pointer.
    slot->data = DN_CAST(void *) DN_AlignDownPowerOfTwo(DN_CAST(uintptr_t) slot + sizeof(DN_PoolSlot) + pool->align, pool->align);

    uintptr_t offset_to_original_ptr = DN_CAST(uintptr_t) slot->data - DN_CAST(uintptr_t) bytes;
    DN_Assert(slot->data > bytes);
    DN_Assert(offset_to_original_ptr <= sizeof(DN_PoolSlot) + pool->align);

    // NOTE: Store the offset to the original pointer behind the user's
    // pointer.
    char *offset_to_original_storage = DN_CAST(char *) slot->data - 1;
    DN_Memcpy(offset_to_original_storage, &offset_to_original_ptr, 1);
  }

  // NOTE: Smuggle the slot type in the next pointer so that we know, when the
  // pointer gets returned which free list to return the pointer to.
  result     = slot->data;
  slot->next = DN_CAST(DN_PoolSlot *) slot_index;
  return result;
}

DN_API DN_Str8 DN_Pool_AllocStr8FV(DN_Pool *pool, DN_FMT_ATTRIB char const *fmt, va_list args)
{
  DN_Str8 result = {};
  if (!DN_Pool_IsValid(pool))
    return result;

  DN_USize size_required = DN_CStr8_FVSize(fmt, args);
  result.data            = DN_CAST(char *) DN_Pool_Alloc(pool, size_required + 1);
  if (result.data) {
    result.size = size_required;
    DN_VSNPrintF(result.data, DN_CAST(int)(result.size + 1), fmt, args);
  }
  return result;
}

DN_API DN_Str8 DN_Pool_AllocStr8F(DN_Pool *pool, DN_FMT_ATTRIB char const *fmt, ...)
{
  va_list args;
  va_start(args, fmt);
  DN_Str8 result = DN_Pool_AllocStr8FV(pool, fmt, args);
  va_end(args);
  return result;
}

DN_API DN_Str8 DN_Pool_AllocStr8Copy(DN_Pool *pool, DN_Str8 string)
{
  DN_Str8 result = {};
  if (!DN_Pool_IsValid(pool))
    return result;

  if (!DN_Str8_HasData(string))
    return result;

  char *data = DN_CAST(char *) DN_Pool_Alloc(pool, string.size + 1);
  if (!data)
    return result;

  DN_Memcpy(data, string.data, string.size);
  data[string.size] = 0;
  result            = DN_Str8_Init(data, string.size);
  return result;
}

DN_API void DN_Pool_Dealloc(DN_Pool *pool, void *ptr)
{
  if (!DN_Pool_IsValid(pool) || !ptr)
    return;

  DN_Assert(DN_Arena_OwnsPtr(pool->arena, ptr));

  char const *one_byte_behind_ptr    = DN_CAST(char *) ptr - 1;
  DN_USize    offset_to_original_ptr = 0;
  DN_Memcpy(&offset_to_original_ptr, one_byte_behind_ptr, 1);
  DN_Assert(offset_to_original_ptr <= sizeof(DN_PoolSlot) + pool->align);

  char           *original_ptr = DN_CAST(char *) ptr - offset_to_original_ptr;
  DN_PoolSlot    *slot         = DN_CAST(DN_PoolSlot *) original_ptr;
  DN_PoolSlotSize slot_index   = DN_CAST(DN_PoolSlotSize)(DN_CAST(uintptr_t) slot->next);
  DN_Assert(slot_index < DN_PoolSlotSize_Count);

  slot->next              = pool->slots[slot_index];
  pool->slots[slot_index] = slot;
}

DN_API void *DN_Pool_Copy(DN_Pool *pool, void const *data, DN_U64 size, uint8_t align)
{
  if (!pool || !data || size == 0)
    return nullptr;

  // TODO: Hmm should align be part of the alloc interface in general? I'm not going to worry
  // about this until we crash because of misalignment.
  DN_Assert(pool->align >= align);

  void *result = DN_Pool_Alloc(pool, size);
  if (result)
    DN_Memcpy(result, data, size);
  return result;
}