realloc!

README.md

@@ -1,28 +1,30 @@
-A `Vec<T: ?Sized>`
+# A `Vec<T: ?Sized>`
 
-It's implemented by laying out the elements in memory contiguously like `alloc::vec::Vec`
+It's implemented by laying out the elements in memory contiguously like [`alloc::vec::Vec`]
 
 # Layout
 
-A `Vechonk` is 3 `usize` long. It owns a single allocation, containing the elements and the metadata.
+A [`Vechonk`] is 3 `usize` long. It owns a single allocation, containing the elements and the metadata.
 The elements are laid out contiguously from the front, while the metadata is laid out contiguously from the back.
 Both grow towards the center until they meet and get realloced to separate them again.
 
 ```txt
-Vechonk<str>
-------------------------
-| ptr   | len   | cap  |
----|---------------------
-   |
-   |___
-       |
-Heap   v
-------------------------------------------------------------------------
-| "hello"   | "uwu"    |  <uninit>       | 0 - 5        | 5 - 3        |
-|-----------|----------|-----------------|--------------|--------------|
-| dynamic   | dynamic  |  rest of alloc  | usize + meta | usize + meta |
---------------------------------------------|--------------|------------
-    ^            ^                          |              |
-    |___________ | _________________________|              |
-                 |_________________________________________|
+
+            Vechonk<str>
+            ------------------------------------
+            | ptr   | len   | cap  | elem_size |
+            ---|---------------|--------|-------
+               |               |        |
+               |               |_______ | ______________________________________
+               |                        |                                      |
+               |               _________|                                      |
+        Heap   v               v                                               v
+        -----------------------|-----------------------------------------------
+value   | "hello"    | "uwu"   |  <uninit>       | 0 - 5        | 5 - 3        |
+        |------------|---------|-----------------|--------------|--------------|
+ size   | dynamic    | dynamic |  rest of alloc  | usize + meta | usize + meta |
+        --------------------------------------------|--------------|------------
+            ^            ^                          |              |
+            |___________ | _________________________|              |
+                         |_________________________________________|
 ```

src/lib.rs

@@ -16,14 +16,15 @@
 //! ```txt
 //!
 //!             Vechonk<str>
-//!             ---------------------------------
-//!             | ptr   | len   | cap  | filled |
-//!             ---|---------------|-------------
-//!                |               |
-//!                |               |________________________________________________
-//!                |                                                               |
-//!         Heap   v                                                               v
-//!         ------------------------------------------------------------------------
+//!             ------------------------------------
+//!             | ptr   | len   | cap  | elem_size |
+//!             ---|---------------|--------|-------
+//!                |               |        |
+//!                |               |_______ | ______________________________________
+//!                |                        |                                      |
+//!                |               _________|                                      |
+//!         Heap   v               v                                               v
+//!         -----------------------|-----------------------------------------------
 //! value   | "hello"    | "uwu"   |  <uninit>       | 0 - 5        | 5 - 3        |
 //!         |------------|---------|-----------------|--------------|--------------|
 //!  size   | dynamic    | dynamic |  rest of alloc  | usize + meta | usize + meta |
@@ -85,7 +86,7 @@ impl<T: ?Sized> Vechonk<T> {
     pub const fn new() -> Self {
         Self {
             // SAFETY: 1 is not 0
-            ptr: unsafe { NonNull::new_unchecked(1 as *mut u8) },
+            ptr: NonNull::dangling(),
             len: 0,
             cap: 0,
             elem_size: 0,
@@ -96,7 +97,7 @@ impl<T: ?Sized> Vechonk<T> {
     /// Create a new Vechonk that allocates `capacity` bytes. `capacity` gets shrunken down
     /// to the next multiple of the alignment of usize + metadata of `T`
     pub fn with_capacity(capacity: usize) -> Self {
-        let capacity = capacity - (capacity % Self::data_align());
+        let capacity = force_align(capacity, Self::data_align());
 
         let mut vechonk = Self::new();
 
@@ -112,6 +113,7 @@ impl<T: ?Sized> Vechonk<T> {
     }
 
     /// Pushes a new element into the [`Vechonk`]. Does panic (for now) if there is no more capacity
+    /// todo: don't take a box but some U that can be unsized into T
     pub fn push(&mut self, element: Box<T>) {
         let elem_size = mem::size_of_val(element.as_ref());
 
@@ -121,7 +123,9 @@ impl<T: ?Sized> Vechonk<T> {
         let data_size = mem::size_of::<PtrData<T>>();
 
         // just panic here instead of a proper realloc
-        assert!(!self.needs_grow(elem_size + data_size));
+        if self.needs_grow(elem_size + data_size) {
+            self.regrow(self.cap + elem_size + data_size);
+        }
 
         let elem_offset = self.elem_size;
 
@@ -166,9 +170,52 @@ impl<T: ?Sized> Vechonk<T> {
         }
     }
 
+    fn regrow(&mut self, min_size: usize) {
+        // new_cap must be properly "aligned" for `PtrData<T>`
+        let new_cap = force_align(min_size * 2, Self::data_align());
+
+        let old_ptr = self.ptr.as_ptr();
+        let old_cap = self.cap;
+
+        let last_data_index = self.len.saturating_sub(1);
+        let old_data_offset = self.offset_for_data(last_data_index);
+
+        // SAFETY: new_cap can't be 0 because of the +1
+        //         We will copy the elements over
+        unsafe {
+            self.grow_to(NonZeroUsize::new_unchecked(new_cap));
+        }
+
+        // copy the elements first
+        // SAFETY: both pointers point to the start of allocations smaller than `self.elem_size` and own them
+        unsafe {
+            ptr::copy_nonoverlapping(old_ptr, self.ptr.as_ptr(), self.elem_size);
+        }
+
+        // then copy the data
+        // SAFETY: both pointers have been offset by less than `self.cap`, and the `data_section_size` fills the allocation perfectly
+        unsafe {
+            let new_data_ptr = self.ptr.as_ptr().add(self.offset_for_data(last_data_index));
+
+            ptr::copy_nonoverlapping(
+                old_ptr.add(old_data_offset),
+                new_data_ptr,
+                self.data_section_size(),
+            )
+        }
+
+        // now free the old data
+        // SAFETY: This was previously allocated and is not used anymore
+        unsafe {
+            Self::dealloc(old_cap, old_ptr);
+        }
+    }
+
     /// Grows the `Vechonk` to a new capacity. This will not copy any elements. This will put the `Vechonk`
     /// into an invalid state, since the `len` is still the length of the old allocation.
     ///
+    /// This doesn't free any memory
+    ///
     /// # Safety
     /// The caller must either set the `len` to zero, or copy the elements to the new allocation by saving
     /// `self.ptr` before calling this function.
@@ -176,7 +223,17 @@ impl<T: ?Sized> Vechonk<T> {
         let layout = Layout::from_size_align(size.get(), Self::data_align()).unwrap();
 
         // SAFETY: layout is guaranteed to have a non-zero size
-        let alloced_ptr = unsafe { alloc::alloc::alloc_zeroed(layout) };
+        let alloced_ptr;
+
+        // we only care about it being zeroed for debugging since it makes it easier
+        #[cfg(debug_assertions)]
+        unsafe {
+            alloced_ptr = alloc::alloc::alloc_zeroed(layout)
+        }
+        #[cfg(not(debug_assertions))]
+        unsafe {
+            alloced_ptr = alloc::alloc::alloc(layout)
+        }
 
         self.ptr =
             NonNull::new(alloced_ptr).unwrap_or_else(|| alloc::alloc::handle_alloc_error(layout));
@@ -201,15 +258,30 @@ impl<T: ?Sized> Vechonk<T> {
 
         // SAFETY: The metadata is only assigned directly from the pointer metadata of the original object and therefore valid
         //         The pointer is calculated from the offset, which is also valid
+        //         The pointer is not aligned btw, todo lol
         unsafe { &*elem_meta_ptr }
     }
 
+    // SAFETY: The allocation must be owned by `ptr` and have the length `cap`
+    unsafe fn dealloc(cap: usize, ptr: *mut u8) {
+        if cap == 0 {
+            return;
+        }
+
+        // SAFETY: Align must be valid since it's obtained using `align_of`
+        let layout =
+            unsafe { Layout::from_size_align_unchecked(cap, mem::align_of::<PtrData<T>>()) };
+
+        unsafe { alloc::alloc::dealloc(ptr, layout) };
+    }
+
     /// Returns a multiple of the alignment of `PtrData<T>`, since `self.cap` is one, and so is the size
     const fn offset_for_data(&self, index: usize) -> usize {
-        self.cap - (mem::size_of::<PtrData<T>>() * (index + 1))
+        self.cap
+            .saturating_sub(mem::size_of::<PtrData<T>>() * (index + 1))
     }
 
-    const fn needs_grow(&self, additional_size: usize) -> bool {
+    fn needs_grow(&self, additional_size: usize) -> bool {
         additional_size > self.cap - (self.elem_size + self.data_section_size())
     }
 
@@ -248,14 +320,9 @@ impl<T: ?Sized> Index<usize> for Vechonk<T> {
 /// don't bother with destructors for now
 impl<T: ?Sized> Drop for Vechonk<T> {
     fn drop(&mut self) {
-        if self.cap == 0 {
-            return;
+        unsafe {
+            Self::dealloc(self.cap, self.ptr.as_ptr());
         }
-
-        // SAFETY: 1 is not 0 and a power of two. `size > usize::MAX` must always be true
-        let layout = Layout::from_size_align(self.cap, mem::align_of::<PtrData<T>>()).unwrap();
-
-        unsafe { alloc::alloc::dealloc(self.ptr.as_ptr(), layout) };
     }
 }
 
@@ -264,3 +331,7 @@ impl<T: ?Sized> Default for Vechonk<T> {
         Self::new()
     }
 }
+
+const fn force_align(size: usize, align: usize) -> usize {
+    size - (size % align)
+}

src/test.rs

@@ -87,3 +87,53 @@ fn index() {
     assert_eq!(hello, "hello");
     assert_eq!(uwu, "uwu");
 }
+
+#[test]
+fn grow_from_empty() {
+    let mut chonk = Vechonk::<str>::new();
+
+    assert_eq!(chonk.len(), 0);
+
+    chonk.push("hello".into());
+    chonk.push("uwu".into());
+
+    let hello = &chonk[0];
+    let uwu = &chonk[1];
+
+    assert_eq!(hello, "hello");
+    assert_eq!(uwu, "uwu");
+
+    assert_eq!(chonk.len(), 2);
+}
+
+#[test]
+fn grow_from_alloc() {
+    let mut chonk = Vechonk::<str>::with_capacity(32);
+
+    assert_eq!(chonk.len(), 0);
+
+    chonk.push("hello".into());
+    chonk.push("uwu".into());
+
+    let hello = &chonk[0];
+    let uwu = &chonk[1];
+
+    assert_eq!(hello, "hello");
+    assert_eq!(uwu, "uwu");
+
+    assert_eq!(chonk.len(), 2);
+}
+
+#[test]
+#[ignore] // alignment...
+fn push_alignment() {
+    use core::any::Any;
+
+    let mut chonk = Vechonk::<dyn Any>::with_capacity(96);
+
+    chonk.push(Box::new(0_u8));
+    chonk.push(Box::new(1_u64));
+
+    let _ = chonk[0];
+    let _ = chonk[1];
+}