From 3739aa54fdd143fcfb5600d06898d447dc247c70 Mon Sep 17 00:00:00 2001
From: Sayan Nandan <nandansayan@outlook.com>
Date: Sun, 4 Jul 2021 21:05:28 +0530
Subject: [PATCH] Add basic `IArray` impl

---
 server/src/coredb/iarray.rs | 109 ++++++++++++++++++++++++++++++++++++
 server/src/coredb/mod.rs    |   1 +
 2 files changed, 110 insertions(+)
 create mode 100644 server/src/coredb/iarray.rs

diff --git a/server/src/coredb/iarray.rs b/server/src/coredb/iarray.rs
new file mode 100644
index 00000000..acc63f75
--- /dev/null
+++ b/server/src/coredb/iarray.rs
@@ -0,0 +1,109 @@
+/*
+ * Created on Sun Jul 04 2021
+ *
+ * This file is a part of Skytable
+ * Skytable (formerly known as TerrabaseDB or Skybase) is a free and open-source
+ * NoSQL database written by Sayan Nandan ("the Author") with the
+ * vision to provide flexibility in data modelling without compromising
+ * on performance, queryability or scalability.
+ *
+ * Copyright (c) 2021, Sayan Nandan <ohsayan@outlook.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+*/
+
+#![allow(dead_code)] // TODO(@ohsayan): Remove this once we're done
+
+use std::mem;
+use std::mem::ManuallyDrop;
+use std::mem::MaybeUninit;
+use std::ptr;
+
+pub trait MemoryBlock {
+    type LayoutItem;
+    fn size() -> usize;
+}
+
+impl<T, const N: usize> MemoryBlock for [T; N] {
+    type LayoutItem = T;
+    fn size() -> usize {
+        N
+    }
+}
+
+pub union InlineArray<A: MemoryBlock> {
+    inline_store: ManuallyDrop<MaybeUninit<A>>,
+    heap_ptr_len: (*mut A::LayoutItem, usize),
+}
+
+impl<A: MemoryBlock> InlineArray<A> {
+    unsafe fn inline_ptr(&self) -> *const A::LayoutItem {
+        self.inline_store.as_ptr() as *const _
+    }
+    unsafe fn inline_ptr_mut(&mut self) -> *mut A::LayoutItem {
+        self.inline_store.as_mut_ptr() as *mut _
+    }
+    fn from_inline(inline_store: MaybeUninit<A>) -> Self {
+        Self {
+            inline_store: ManuallyDrop::new(inline_store),
+        }
+    }
+    fn from_heap_ptr(start_ptr: *mut A::LayoutItem, len: usize) -> Self {
+        Self {
+            heap_ptr_len: (start_ptr, len),
+        }
+    }
+}
+
+pub struct IArray<A: MemoryBlock> {
+    cap: usize,
+    store: InlineArray<A>,
+}
+
+impl<A: MemoryBlock> IArray<A> {
+    pub fn new() -> IArray<A> {
+        Self {
+            cap: 0,
+            store: InlineArray::from_inline(MaybeUninit::uninit()),
+        }
+    }
+    pub fn from_vec(mut vec: Vec<A::LayoutItem>) -> Self {
+        if vec.capacity() <= Self::inline_capacity() {
+            let mut store = InlineArray::<A>::from_inline(MaybeUninit::uninit());
+            let len = vec.len();
+            unsafe {
+                ptr::copy_nonoverlapping(vec.as_ptr(), store.inline_ptr_mut(), len);
+            }
+            // done with the copy
+            Self { cap: len, store }
+        } else {
+            let (start_ptr, cap, len) = (vec.as_mut_ptr(), vec.capacity(), vec.len());
+            // leak the vec
+            mem::forget(vec);
+            IArray {
+                cap,
+                store: InlineArray::from_heap_ptr(start_ptr, len),
+            }
+        }
+    }
+    fn inline_capacity() -> usize {
+        if mem::size_of::<A::LayoutItem>() > 0 {
+            // not a ZST, so cap of array
+            A::size()
+        } else {
+            usize::MAX
+        }
+    }
+}
diff --git a/server/src/coredb/mod.rs b/server/src/coredb/mod.rs
index 0819f957..0ff8394d 100644
--- a/server/src/coredb/mod.rs
+++ b/server/src/coredb/mod.rs
@@ -39,6 +39,7 @@ pub use htable::Data;
 use libsky::TResult;
 use std::sync::Arc;
 pub mod htable;
+pub mod iarray;
 pub mod lazy;
 pub mod lock;
 mod memstore;