From 59dac01e4eaebd01714b6640ae2cd656796147fb Mon Sep 17 00:00:00 2001
From: Trevor Norris <trev.norris@gmail.com>
Date: Mon, 9 Sep 2013 19:39:21 -0700
Subject: [PATCH] buffer: optimize common encoding cases

String#toLowerCase() is incredibly slow and was costing a 15-30%
performance hit for Buffers less than 1KB. Now instead it'll attempt to
find the correct encoding directly from the passed encoding, only then
afterwards it'll lowercase.

The optimization for not passing any encoding at all is still at the top
of the method.

At most this may add 10% performance hit for passing a mixed case
encoding.
---
 lib/buffer.js | 50 ++++++++++++++++++++++++++++----------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/lib/buffer.js b/lib/buffer.js
index dfd79e6290..de0ab040dd 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -202,40 +202,46 @@ Buffer.prototype.parent = undefined;
 
 // toString(encoding, start=0, end=buffer.length)
 Buffer.prototype.toString = function(encoding, start, end) {
-  encoding = !!encoding ? (encoding + '').toLowerCase() : 'utf8';
+  var loweredCase = false;
 
-  start = ~~start;
-  end = util.isUndefined(end) ? this.length : ~~end;
+  start = start >>> 0;
+  end = util.isUndefined(end) ? this.length : end >>> 0;
 
+  if (!encoding) encoding = 'utf8';
   if (start < 0) start = 0;
   if (end > this.length) end = this.length;
   if (end <= start) return '';
 
-  switch (encoding) {
-    case 'hex':
-      return this.hexSlice(start, end);
+  while (true) {
+    switch (encoding) {
+      case 'hex':
+        return this.hexSlice(start, end);
 
-    case 'utf8':
-    case 'utf-8':
-      return this.utf8Slice(start, end);
+      case 'utf8':
+      case 'utf-8':
+        return this.utf8Slice(start, end);
 
-    case 'ascii':
-      return this.asciiSlice(start, end);
+      case 'ascii':
+        return this.asciiSlice(start, end);
 
-    case 'binary':
-      return this.binarySlice(start, end);
+      case 'binary':
+        return this.binarySlice(start, end);
 
-    case 'base64':
-      return this.base64Slice(start, end);
+      case 'base64':
+        return this.base64Slice(start, end);
 
-    case 'ucs2':
-    case 'ucs-2':
-    case 'utf16le':
-    case 'utf-16le':
-      return this.ucs2Slice(start, end);
+      case 'ucs2':
+      case 'ucs-2':
+      case 'utf16le':
+      case 'utf-16le':
+        return this.ucs2Slice(start, end);
 
-    default:
-      throw new TypeError('Unknown encoding: ' + encoding);
+      default:
+        if (loweredCase)
+          throw new TypeError('Unknown encoding: ' + encoding);
+        encoding = (encoding + '').toLowerCase();
+        loweredCase = true;
+    }
   }
 };