slightly optimize writing tags to memory

simdnbt/src/borrow/compound.rs

@@ -1,4 +1,4 @@
-use std::io::Cursor;
+use std::{io::Cursor, mem::MaybeUninit};
 
 use byteorder::ReadBytesExt;
 
@@ -33,6 +33,12 @@ impl<'a> NbtCompound<'a> {
         }
 
         let mut tags = alloc.get().named.start(depth);
+
+        let mut tags_buffer = unsafe {
+            MaybeUninit::<[MaybeUninit<(&Mutf8Str, NbtTag<'a>)>; 4]>::uninit().assume_init()
+        };
+        let mut tags_buffer_len: usize = 0;
+
         loop {
             let tag_type = match data.read_u8() {
                 Ok(tag_type) => tag_type,
@@ -61,8 +67,23 @@ impl<'a> NbtCompound<'a> {
                     return Err(e);
                 }
             };
-            tags.push((tag_name, tag));
+
+            tags_buffer[tags_buffer_len] = MaybeUninit::new((tag_name, tag));
+            tags_buffer_len += 1;
+
+            if tags_buffer_len == tags_buffer.len() {
+                // writing the tags in groups like this is slightly faster
+                for i in 0..tags_buffer_len {
+                    tags.push(unsafe { tags_buffer.get_unchecked(i).assume_init_read() });
                 }
+                tags_buffer_len = 0;
+            }
+        }
+
+        for i in 0..tags_buffer_len {
+            tags.push(unsafe { tags_buffer.get_unchecked(i).assume_init_read() });
+        }
+
         let values = alloc.get().named.finish(tags, depth);
 
         Ok(Self { values })

simdnbt/src/borrow/tag_alloc.rs

@@ -231,6 +231,21 @@ impl<T> ContiguousTagsAllocator<T> {
         self.alloc.len = self.size;
     }
 
+    #[inline]
+    pub fn extend_from_slice(&mut self, slice: &[T]) {
+        while self.alloc.len + slice.len() > self.alloc.cap {
+            self.grow();
+        }
+
+        // copy the slice
+        unsafe {
+            let end = self.alloc.ptr.as_ptr().add(self.alloc.len);
+            std::ptr::copy_nonoverlapping(slice.as_ptr(), end, slice.len());
+        }
+        self.alloc.len += slice.len();
+        self.size += slice.len();
+    }
+
     #[inline]
     pub fn push(&mut self, value: T) {
         // check if we need to reallocate