util: refactor format method.Performance improved.

Method format refactored to make it more maintenable, replacing the
switch by a function factory, that returns the appropiated function
given the character (d, i , f, j, s).

Also, performance when formatting an string that contains several
consecutive % symbols is improved. The test:
`const numSamples = 10000000;
const strPercents = '%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%s%%%%%%%%%%%%%%%%%i%%%%%%%%%%%%%%%%%%%%%%%%%%';
var s;
console.time('Percents');
for (let i = 0; i < numSamples; i++) {
  s = util.format(strPercents, 'test', 12);
}
console.timeEnd('Percents');`

Original time:   28399.708ms
After refactor:  23763.788ms
Improved: 16%

PR-URL: #12407
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Brian White <mscdex@mscdex.net>

lib/util.js

@@ -68,71 +68,59 @@ exports.format = function(f) {
     return objects.join(' ');
   }
 
-  var argLen = arguments.length;
-
-  if (argLen === 1) return f;
+  if (arguments.length === 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) {
+      if (f.charCodeAt(i + 1) !== 37/*'%'*/ && a >= arguments.length) {
+        ++i;
+        continue;
+      }
       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;
+          break;
         case 105: // 'i'
-          if (a >= argLen)
-            break;
           if (lastPos < i)
             str += f.slice(lastPos, i);
           str += parseInt(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
+          break;
         case 102: // 'f'
-          if (a >= argLen)
-            break;
           if (lastPos < i)
             str += f.slice(lastPos, i);
           str += parseFloat(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
+          break;
         case 106: // 'j'
-          if (a >= argLen)
-            break;
           if (lastPos < i)
             str += f.slice(lastPos, i);
           str += tryStringify(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
+          break;
         case 115: // 's'
-          if (a >= argLen)
-            break;
           if (lastPos < i)
             str += f.slice(lastPos, i);
           str += String(arguments[a++]);
-          lastPos = i = i + 2;
-          continue;
+          break;
         case 37: // '%'
           if (lastPos < i)
             str += f.slice(lastPos, i);
           str += '%';
-          lastPos = i = i + 2;
-          continue;
+          break;
       }
+      lastPos = i = i + 2;
+      continue;
     }
     ++i;
   }
   if (lastPos === 0)
     str = f;
   else if (lastPos < f.length)
     str += f.slice(lastPos);
-  while (a < argLen) {
+  while (a < arguments.length) {
     const x = arguments[a++];
     if (x === null || (typeof x !== 'object' && typeof x !== 'symbol')) {
       str += ' ' + x;

test/parallel/test-util-format.js

@@ -106,6 +106,8 @@ assert.strictEqual(util.format('%%s%s', 'foo'), '%sfoo');
 assert.strictEqual(util.format('%s:%s'), '%s:%s');
 assert.strictEqual(util.format('%s:%s', undefined), 'undefined:%s');
 assert.strictEqual(util.format('%s:%s', 'foo'), 'foo:%s');
+assert.strictEqual(util.format('%s:%i', 'foo'), 'foo:%i');
+assert.strictEqual(util.format('%s:%f', 'foo'), 'foo:%f');
 assert.strictEqual(util.format('%s:%s', 'foo', 'bar'), 'foo:bar');
 assert.strictEqual(util.format('%s:%s', 'foo', 'bar', 'baz'), 'foo:bar baz');
 assert.strictEqual(util.format('%%%s%%', 'hi'), '%hi%');
@@ -114,6 +116,12 @@ assert.strictEqual(util.format('%sbc%%def', 'a'), 'abc%def');
 assert.strictEqual(util.format('%d:%d', 12, 30), '12:30');
 assert.strictEqual(util.format('%d:%d', 12), '12:%d');
 assert.strictEqual(util.format('%d:%d'), '%d:%d');
+assert.strictEqual(util.format('%i:%i', 12, 30), '12:30');
+assert.strictEqual(util.format('%i:%i', 12), '12:%i');
+assert.strictEqual(util.format('%i:%i'), '%i:%i');
+assert.strictEqual(util.format('%f:%f', 12, 30), '12:30');
+assert.strictEqual(util.format('%f:%f', 12), '12:%f');
+assert.strictEqual(util.format('%f:%f'), '%f:%f');
 assert.strictEqual(util.format('o: %j, a: %j', {}, []), 'o: {}, a: []');
 assert.strictEqual(util.format('o: %j, a: %j', {}), 'o: {}, a: %j');
 assert.strictEqual(util.format('o: %j, a: %j'), 'o: %j, a: %j');