buffer: optimize createFromString

PR-URL: nodejs#54324

benchmark/buffers/buffer-from.js

@@ -4,16 +4,16 @@ const common = require('../common.js');
 const assert = require('assert');
 const bench = common.createBenchmark(main, {
   source: [
-    'array',
-    'arraybuffer',
-    'arraybuffer-middle',
-    'buffer',
+    // 'array',
+    // 'arraybuffer',
+    // 'arraybuffer-middle',
+    // 'buffer',
     'string',
     'string-utf8',
     'string-base64',
-    'object',
-    'uint8array',
-    'uint16array',
+    // 'object',
+    // 'uint8array',
+    // 'uint16array',
   ],
   len: [100, 2048],
   n: [8e5],

lib/buffer.js

@@ -442,27 +442,37 @@ function allocate(size) {
 }
 
 function fromStringFast(string, ops) {
-  const length = ops.byteLength(string);
+  const stringLength = string.length
 
-  if (length >= (Buffer.poolSize >>> 1))
+  if (stringLength > Buffer.poolSize)
+    return createFromString(string, ops.encodingVal);
+
+  let length = stringLength * 4; // max utf8 byte length
+
+  if (length > Buffer.poolSize)
+    length = ops.byteLength(string);
+
+  if (length * 2 > Buffer.poolSize)
     return createFromString(string, ops.encodingVal);
 
   if (length > (poolSize - poolOffset))
     createPool();
+
   let b = new FastBuffer(allocPool, poolOffset, length);
   const actual = ops.write(b, string, 0, length);
   if (actual !== length) {
-    // byteLength() may overestimate. That's a rare case, though.
     b = new FastBuffer(allocPool, poolOffset, actual);
   }
+
   poolOffset += actual;
   alignPool();
+
   return b;
 }
 
 function fromString(string, encoding) {
   let ops;
-  if (typeof encoding !== 'string' || encoding.length === 0) {
+  if (typeof encoding !== 'string' || encoding === 'utf8' || encoding.length === 0) {
     if (string.length === 0)
       return new FastBuffer();
     ops = encodingOps.utf8;