From 7843e2792dce0f20d23b3c1cca51652013bef0ea Mon Sep 17 00:00:00 2001
From: Tobias Bieniek <tobias.bieniek@gmail.com>
Date: Wed, 14 Nov 2018 11:26:00 +0100
Subject: [PATCH] core/char: Add comment to `to_digit()`

---
 src/libcore/char/methods.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/libcore/char/methods.rs b/src/libcore/char/methods.rs
index 4207b3c776c..d6fcff644ac 100644
--- a/src/libcore/char/methods.rs
+++ b/src/libcore/char/methods.rs
@@ -122,6 +122,9 @@ pub fn is_digit(self, radix: u32) -> bool {
     #[inline]
     pub fn to_digit(self, radix: u32) -> Option<u32> {
         assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
+
+        // the code is split up here to improve execution speed for cases where
+        // the `radix` is constant and 10 or smaller
         let val = if radix <= 10  {
             match self {
                 '0' ..= '9' => self as u32 - '0' as u32,