From 0f0dffb24e85780dee0ff824a3375d707aa80d89 Mon Sep 17 00:00:00 2001
From: Jan de Mooij <jdemooij@mozilla.com>
Date: Wed, 22 Apr 2015 11:30:47 +0200
Subject: [PATCH] Bug 1156886 - Optimize toLowerCase and toUpperCase on ASCII
 characters. r=luke

---
 js/src/jsstr.cpp    |  4 ++--
 js/src/vm/Unicode.h | 30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index 1cd2be6b8e7..7752217af04 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -603,7 +603,7 @@ ToLowerCase(JSContext* cx, JSLinearString* str)
         size_t i = 0;
         for (; i < length; i++) {
             char16_t c = chars[i];
-            if (unicode::ToLowerCase(c) != c)
+            if (unicode::CanLowerCase(c))
                 break;
         }
 
@@ -722,7 +722,7 @@ ToUpperCase(JSContext* cx, JSLinearString* str)
         size_t i = 0;
         for (; i < length; i++) {
             char16_t c = chars[i];
-            if (unicode::ToUpperCase(c) != c)
+            if (unicode::CanUpperCase(c))
                 break;
         }
 
diff --git a/js/src/vm/Unicode.h b/js/src/vm/Unicode.h
index 591e46f56e2..ea853442c7f 100644
--- a/js/src/vm/Unicode.h
+++ b/js/src/vm/Unicode.h
@@ -191,6 +191,12 @@ IsSpaceOrBOM2(char16_t ch)
 inline char16_t
 ToUpperCase(char16_t ch)
 {
+    if (ch < 128) {
+        if (ch >= 'a' && ch <= 'z')
+            return ch - ('a' - 'A');
+        return ch;
+    }
+
     const CharacterInfo& info = CharInfo(ch);
 
     return uint16_t(ch) + info.upperCase;
@@ -199,11 +205,35 @@ ToUpperCase(char16_t ch)
 inline char16_t
 ToLowerCase(char16_t ch)
 {
+    if (ch < 128) {
+        if (ch >= 'A' && ch <= 'Z')
+            return ch + ('a' - 'A');
+        return ch;
+    }
+
     const CharacterInfo& info = CharInfo(ch);
 
     return uint16_t(ch) + info.lowerCase;
 }
 
+// Returns true iff ToUpperCase(ch) != ch.
+inline bool
+CanUpperCase(char16_t ch)
+{
+    if (ch < 128)
+        return ch >= 'a' && ch <= 'z';
+    return CharInfo(ch).upperCase != 0;
+}
+
+// Returns true iff ToLowerCase(ch) != ch.
+inline bool
+CanLowerCase(char16_t ch)
+{
+    if (ch < 128)
+        return ch >= 'A' && ch <= 'Z';
+    return CharInfo(ch).lowerCase != 0;
+}
+
 } /* namespace unicode */
 } /* namespace js */