From 09f8468acffd281d566f9c38a08c46f9d9345e8b Mon Sep 17 00:00:00 2001
From: Andrew Duffy <andreweduffy@gmail.com>
Date: Tue, 20 Aug 2024 12:48:44 -0400
Subject: [PATCH] doc

---
 src/lib.rs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index 31c5482..82ed0d7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -332,13 +332,16 @@ pub struct Compressor {
 
 impl Default for Compressor {
     fn default() -> Self {
+        // NOTE: `vec!` has a specialization for building a new vector of `0u64`. Because Symbol and u64
+        //  have the same bit pattern, we can allocate as u64 and transmute. If we do `vec![Symbol::EMPTY; N]`,
+        // that will create a new Vec and call `Symbol::EMPTY.clone()` `N` times which is considerably slower.
         let symbols = vec![0u64; 511];
         // SAFETY: transmute safety assured by the compiler.
         let symbols: Vec<Symbol> = unsafe { std::mem::transmute(symbols) };
         let mut table = Self {
             symbols,
             n_symbols: 0,
-            codes_twobyte: [CodeMeta::EMPTY].repeat(65_536),
+            codes_twobyte: vec![CodeMeta::EMPTY; 65_536],
             lossy_pht: LossyPHT::new(),
         };