buffer: improve from() performance

PR-URL: https://github.com/nodejs/node/pull/31615
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/buffer.js

@@ -452,14 +452,6 @@ function fromString(string, encoding) {
   return fromStringFast(string, ops);
 }
 
-function fromArrayLike(obj) {
-  const length = obj.length;
-  const b = allocate(length);
-  for (let i = 0; i < length; i++)
-    b[i] = obj[i];
-  return b;
-}
-
 function fromArrayBuffer(obj, byteOffset, length) {
   // Convert byteOffset to integer
   if (byteOffset === undefined) {
@@ -491,17 +483,22 @@ function fromArrayBuffer(obj, byteOffset, length) {
   return new FastBuffer(obj, byteOffset, length);
 }
 
-function fromObject(obj) {
-  if (isUint8Array(obj)) {
-    const b = allocate(obj.length);
-
-    if (b.length === 0)
-      return b;
-
-    _copy(obj, b, 0, 0, obj.length);
+function fromArrayLike(obj) {
+  if (obj.length <= 0)
+    return new FastBuffer();
+  if (obj.length < (Buffer.poolSize >>> 1)) {
+    if (obj.length > (poolSize - poolOffset))
+      createPool();
+    const b = new FastBuffer(allocPool, poolOffset, obj.length);
+    b.set(obj, 0);
+    poolOffset += obj.length;
+    alignPool();
     return b;
   }
+  return new FastBuffer(obj);
+}
 
+function fromObject(obj) {
   if (obj.length !== undefined || isAnyArrayBuffer(obj.buffer)) {
     if (typeof obj.length !== 'number') {
       return new FastBuffer();