buffer: optimize createFromString

PR-URL: #54324

Author: ronag

lib/buffer.js

@@ -150,11 +150,12 @@ const constants = ObjectDefineProperties({}, {
 });
 
 Buffer.poolSize = 8 * 1024;
-let poolSize, poolOffset, allocPool;
+let poolSize, poolOffset, allocPool, allocBuffer;
 
 function createPool() {
   poolSize = Buffer.poolSize;
-  allocPool = createUnsafeBuffer(poolSize).buffer;
+  allocBuffer = createUnsafeBuffer(poolSize);
+  allocPool = allocBuffer.buffer;
   markAsUntransferable(allocPool);
   poolOffset = 0;
 }
@@ -442,27 +443,35 @@ function allocate(size) {
 }
 
 function fromStringFast(string, ops) {
-  const length = ops.byteLength(string);
+  const maxLength = Buffer.poolSize >>> 1;
 
-  if (length >= (Buffer.poolSize >>> 1))
+  let length = string.length; // Min length
+
+  if (length >= maxLength)
+    return createFromString(string, ops.encodingVal);
+
+  length *= 4; // Max length (4 bytes per character)
+
+  if (length >= maxLength)
+    length = ops.byteLength(string); // Actual length
+
+  if (length >= maxLength)
     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);
-  }
+
+  const actual = ops.write(allocBuffer, string, poolOffset, length);
+  const 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 (!encoding || encoding === 'utf8' || typeof encoding !== 'string') {
     if (string.length === 0)
       return new FastBuffer();
     ops = encodingOps.utf8;