(chunk_t* chunk, void* p) {   if(chunk->size >= HEAP_SIZECLASSES)   {     chunk->shallow = 0;   } else {     // Calculate the external pointer.     void* ext = EXTERNAL_PTR(p, chunk->size);      // Shift to account for smallest allocation size.     uint00_t slot = FIND_SLOT(ext, chunk->m);      // A clear bit is in-use, a set bit is available.     