From 576a1cc1bfa539e23343028700c812492bc1508a Mon Sep 17 00:00:00 2001
From: mat <git@matdoes.dev>
Date: Sat, 18 Jan 2025 18:30:59 +0000
Subject: [PATCH] minor optimization by using push_unchecked for the first tape
 push

---
 simdnbt/src/borrow/mod.rs  | 34 ++++++++++++++++++++++------------
 simdnbt/src/borrow/tape.rs |  5 +++++
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/simdnbt/src/borrow/mod.rs b/simdnbt/src/borrow/mod.rs
index a49d1bc..950b1c2 100644
--- a/simdnbt/src/borrow/mod.rs
+++ b/simdnbt/src/borrow/mod.rs
@@ -53,12 +53,17 @@ pub fn read<'a>(data: &mut Cursor<&'a [u8]>) -> Result<Nbt<'a>, Error> {
     stack.push(ParsingStackElement::Compound {
         index_of_compound_element: 0,
     })?;
-    tapes.main.push(TapeElement::new_with_approx_len_and_offset(
-        TapeTagKind::Compound,
-        // these get overwritten later
-        0,
-        0,
-    ));
+    unsafe {
+        // SAFETY: we just created the MainTape so there's definitely space for an item
+        tapes
+            .main
+            .push_unchecked(TapeElement::new_with_approx_len_and_offset(
+                TapeTagKind::Compound,
+                // these get overwritten later
+                0,
+                0,
+            ))
+    };
 
     read_with_stack(&mut data, &mut tapes, &mut stack)?;
 
@@ -91,12 +96,17 @@ pub fn read_compound<'a>(data: &mut Cursor<&'a [u8]>) -> Result<BaseNbtCompound<
     stack.push(ParsingStackElement::Compound {
         index_of_compound_element: 0,
     })?;
-    tapes.main.push(TapeElement::new_with_approx_len_and_offset(
-        TapeTagKind::Compound,
-        // these get overwritten later
-        0,
-        0,
-    ));
+    unsafe {
+        // SAFETY: we just created the MainTape so there's definitely space for an item
+        tapes
+            .main
+            .push_unchecked(TapeElement::new_with_approx_len_and_offset(
+                TapeTagKind::Compound,
+                // these get overwritten later
+                0,
+                0,
+            ))
+    };
 
     read_with_stack(&mut data, &mut tapes, &mut stack)?;
 
diff --git a/simdnbt/src/borrow/tape.rs b/simdnbt/src/borrow/tape.rs
index f47c6a1..8599adc 100644
--- a/simdnbt/src/borrow/tape.rs
+++ b/simdnbt/src/borrow/tape.rs
@@ -53,6 +53,11 @@ impl<A: Allocator> MainTape<A> {
             self.end = unsafe { self.cur.add(extending_by) };
         }
 
+        unsafe { self.push_unchecked(element) };
+    }
+
+    #[inline]
+    pub unsafe fn push_unchecked(&mut self, element: TapeElement) {
         unsafe { self.cur.write(element) };
         self.cur = unsafe { self.cur.add(1) };
     }