From 8d72b0d291e603c3b62b637a314a5ee35ba95fdc Mon Sep 17 00:00:00 2001
From: Evan Lucas <evanlucas@me.com>
Date: Mon, 22 Feb 2016 02:55:55 -0600
Subject: [PATCH 1/2] util: improve util.format performance

By manually copying arguments and breaking the try/catch out, we are
able to improve the performance of util.format by 20-100% (depending on
the types).

PR-URL: https://github.com/nodejs/node/pull/5360
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 lib/util.js | 35 ++++++++++++++++++++++-------------
 1 file changed, 22 insertions(+), 13 deletions(-)

diff --git a/lib/util.js b/lib/util.js
index 1425cc6b504c15..a971c103d4ecd7 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -9,39 +9,48 @@ const isError = internalUtil.isError;
 
 var Debug;
 
+function tryStringify(arg) {
+  try {
+    return JSON.stringify(arg);
+  } catch (_) {
+    return '[Circular]';
+  }
+}
+
 const formatRegExp = /%[sdj%]/g;
 exports.format = function(f) {
   if (typeof f !== 'string') {
-    var objects = [];
+    const objects = new Array(arguments.length);
     for (var index = 0; index < arguments.length; index++) {
-      objects.push(inspect(arguments[index]));
+      objects[index] = inspect(arguments[index]);
     }
     return objects.join(' ');
   }
 
   if (arguments.length === 1) return f;
 
-  var i = 1;
-  var args = arguments;
-  var len = args.length;
-  var str = String(f).replace(formatRegExp, function(x) {
+  const len = arguments.length;
+  const args = new Array(len);
+  var i;
+  for (i = 0; i < len; i++) {
+    args[i] = arguments[i];
+  }
+
+  i = 1;
+  var str = f.replace(formatRegExp, function(x) {
     if (x === '%%') return '%';
     if (i >= len) return x;
     switch (x) {
       case '%s': return String(args[i++]);
       case '%d': return Number(args[i++]);
-      case '%j':
-        try {
-          return JSON.stringify(args[i++]);
-        } catch (_) {
-          return '[Circular]';
-        }
+      case '%j': return tryStringify(args[i++]);
         // falls through
       default:
         return x;
     }
   });
-  for (var x = args[i]; i < len; x = args[++i]) {
+  while (i < len) {
+    const x = args[i++];
     if (x === null || (typeof x !== 'object' && typeof x !== 'symbol')) {
       str += ' ' + x;
     } else {

From c490b8ba54df6c730f7bfd02aaafe7c34f571f9e Mon Sep 17 00:00:00 2001
From: Brian White <mscdex@mscdex.net>
Date: Mon, 22 Feb 2016 20:47:20 -0500
Subject: [PATCH 2/2] util: improve format() performance further

Replacing the regexp and replace function with a loop improves
performance by ~60-200%.

PR-URL: https://github.com/nodejs/node/pull/5360
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 lib/util.js | 73 +++++++++++++++++++++++++++++++++++------------------
 1 file changed, 49 insertions(+), 24 deletions(-)

diff --git a/lib/util.js b/lib/util.js
index a971c103d4ecd7..42661608ddf7f5 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -17,7 +17,6 @@ function tryStringify(arg) {
   }
 }
 
-const formatRegExp = /%[sdj%]/g;
 exports.format = function(f) {
   if (typeof f !== 'string') {
     const objects = new Array(arguments.length);
@@ -27,30 +26,56 @@ exports.format = function(f) {
     return objects.join(' ');
   }
 
-  if (arguments.length === 1) return f;
-
-  const len = arguments.length;
-  const args = new Array(len);
-  var i;
-  for (i = 0; i < len; i++) {
-    args[i] = arguments[i];
-  }
-
-  i = 1;
-  var str = f.replace(formatRegExp, function(x) {
-    if (x === '%%') return '%';
-    if (i >= len) return x;
-    switch (x) {
-      case '%s': return String(args[i++]);
-      case '%d': return Number(args[i++]);
-      case '%j': return tryStringify(args[i++]);
-        // falls through
-      default:
-        return x;
+  var argLen = arguments.length;
+
+  if (argLen === 1) return f;
+
+  var str = '';
+  var a = 1;
+  var lastPos = 0;
+  for (var i = 0; i < f.length;) {
+    if (f.charCodeAt(i) === 37/*'%'*/ && i + 1 < f.length) {
+      switch (f.charCodeAt(i + 1)) {
+        case 100: // 'd'
+          if (a >= argLen)
+            break;
+          if (lastPos < i)
+            str += f.slice(lastPos, i);
+          str += Number(arguments[a++]);
+          lastPos = i = i + 2;
+          continue;
+        case 106: // 'j'
+          if (a >= argLen)
+            break;
+          if (lastPos < i)
+            str += f.slice(lastPos, i);
+          str += tryStringify(arguments[a++]);
+          lastPos = i = i + 2;
+          continue;
+        case 115: // 's'
+          if (a >= argLen)
+            break;
+          if (lastPos < i)
+            str += f.slice(lastPos, i);
+          str += String(arguments[a++]);
+          lastPos = i = i + 2;
+          continue;
+        case 37: // '%'
+          if (lastPos < i)
+            str += f.slice(lastPos, i);
+          str += '%';
+          lastPos = i = i + 2;
+          continue;
+      }
     }
-  });
-  while (i < len) {
-    const x = args[i++];
+    ++i;
+  }
+  if (lastPos === 0)
+    str = f;
+  else if (lastPos < f.length)
+    str += f.slice(lastPos);
+  while (a < argLen) {
+    const x = arguments[a++];
     if (x === null || (typeof x !== 'object' && typeof x !== 'symbol')) {
       str += ' ' + x;
     } else {