From a7c0897a398daa9093c5e246cad69f8ebd1a413f Mon Sep 17 00:00:00 2001
From: Pazzaz <pazzaz.sundqvist@gmail.com>
Date: Wed, 4 Jul 2018 20:35:33 +0200
Subject: [PATCH 1/3] Only convert `char`s that need it in str case conversion
 methods.

---
 src/liballoc/str.rs | 56 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 46 insertions(+), 10 deletions(-)

diff --git a/src/liballoc/str.rs b/src/liballoc/str.rs
index bb99d0401d3cd..8f79af9a35367 100644
--- a/src/liballoc/str.rs
+++ b/src/liballoc/str.rs
@@ -360,18 +360,35 @@ impl str {
     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
     pub fn to_lowercase(&self) -> String {
         let mut s = String::with_capacity(self.len());
+        let mut lower = 0;
         for (i, c) in self[..].char_indices() {
-            if c == 'Σ' {
-                // Σ maps to σ, except at the end of a word where it maps to ς.
-                // This is the only conditional (contextual) but language-independent mapping
-                // in `SpecialCasing.txt`,
-                // so hard-code it rather than have a generic "condition" mechanism.
-                // See https://github.com/rust-lang/rust/issues/26035
-                map_uppercase_sigma(self, i, &mut s)
-            } else {
-                s.extend(c.to_lowercase());
+            // Lowercase `char`s are inserted into `s` in slices,
+            // uppercase `char`s are converted to lowercase and inserted individually.
+            if c.is_uppercase() {
+                if lower != i {
+                    unsafe {
+                        // lower..i is an interval of lowercase `char`s before `c`.
+                        s.push_str((lower..i).get_unchecked(self));
+                    }
+                }
+                if c == 'Σ' {
+                    // Σ maps to σ, except at the end of a word where it maps to ς.
+                    // This is the only conditional (contextual) but language-independent mapping
+                    // in `SpecialCasing.txt`,
+                    // so hard-code it rather than have a generic "condition" mechanism.
+                    // See https://github.com/rust-lang/rust/issues/26035
+                    map_uppercase_sigma(self, i, &mut s);
+                } else {
+                    s.extend(c.to_lowercase());
+                }
+                
+                // The next possible interval of lowercase `char`s start after `c`.
+                lower = i + c.len_utf8();
             }
         }
+        unsafe {
+            s.push_str((lower..self.len()).get_unchecked(self));
+        }
         return s;
 
         fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
@@ -423,7 +440,26 @@ impl str {
     #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
     pub fn to_uppercase(&self) -> String {
         let mut s = String::with_capacity(self.len());
-        s.extend(self.chars().flat_map(|c| c.to_uppercase()));
+        let mut lower = 0;
+        for (i, c) in self[..].char_indices() {
+            // Uppercase `char`s are inserted into `s` in slices,
+            // lowercase `char`s are converted to uppercase and inserted individually.
+            if c.is_lowercase() {
+                if lower != i {
+                    unsafe {
+                        // lower..i is an interval of uppercase `char`s before `c`.
+                        s.push_str((lower..i).get_unchecked(self));
+                    }
+                }
+                s.extend(c.to_uppercase());
+
+                // The next possible interval of uppercase `char`s start after `c`.
+                lower = i + c.len_utf8();
+            }
+        }
+        unsafe {
+            s.push_str((lower..self.len()).get_unchecked(self));
+        }
         return s;
     }
 

From 3e49134027dcc436ecaf978198b1f15bef9996af Mon Sep 17 00:00:00 2001
From: Pazzaz <pazzaz.sundqvist@gmail.com>
Date: Wed, 4 Jul 2018 22:14:12 +0200
Subject: [PATCH 2/3] Enable feature slice_index_methods in liballoc

---
 src/liballoc/lib.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 493448eaf88fa..2d3a9569f49ba 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -106,6 +106,7 @@
 #![feature(ptr_internals)]
 #![feature(ptr_offset_from)]
 #![feature(rustc_attrs)]
+#![feature(slice_index_methods)]
 #![feature(specialization)]
 #![feature(split_ascii_whitespace)]
 #![feature(staged_api)]

From fde8e5935dbed480e8f1f6469f7ba780c163c492 Mon Sep 17 00:00:00 2001
From: Pazzaz <pazzaz.sundqvist@gmail.com>
Date: Wed, 4 Jul 2018 22:29:13 +0200
Subject: [PATCH 3/3] Trim trailing whitespace

---
 src/liballoc/str.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/liballoc/str.rs b/src/liballoc/str.rs
index 8f79af9a35367..9ac7fd0dcda2d 100644
--- a/src/liballoc/str.rs
+++ b/src/liballoc/str.rs
@@ -381,7 +381,7 @@ impl str {
                 } else {
                     s.extend(c.to_lowercase());
                 }
-                
+
                 // The next possible interval of lowercase `char`s start after `c`.
                 lower = i + c.len_utf8();
             }