buffer: optimize writing short strings

Author: ronag

benchmark/buffers/buffer-write-string.js

@@ -3,10 +3,10 @@
 const common = require('../common.js');
 const bench = common.createBenchmark(main, {
   encoding: [
-    '', 'utf8', 'ascii', 'hex', 'utf16le', 'latin1',
+    'utf8',
   ],
-  args: [ '', 'offset', 'offset+length' ],
-  len: [2048],
+  args: [ '' ],
+  len: [1,8,16,32, 64],
   n: [1e6],
 });
 

lib/buffer.js

@@ -1108,6 +1108,24 @@ Buffer.prototype.write = function write(string, offset, length, encoding) {
     }
   }
 
+  const len = string.length;
+  if (len <= 32 && len <= length) {
+    let n = 0;
+    while (true) {
+      const code = string.charCodeAt(n);
+      if (code >= 128) {
+        break;
+      }
+
+      this[offset + n] = code;
+      n++;
+
+      if (n === len) {
+        return len;
+      }
+    }
+  }
+
   if (!encoding)
     return this.utf8Write(string, offset, length);