benchmark: move string-decoder to its own category

PR-URL: https://github.com/nodejs/node/pull/5177
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>

benchmark/string_decoder/string-decoder.js

@@ -0,0 +1,61 @@
+'use strict';
+var common = require('../common.js');
+var StringDecoder = require('string_decoder').StringDecoder;
+
+var bench = common.createBenchmark(main, {
+  encoding: ['ascii', 'utf8', 'base64-utf8', 'base64-ascii'],
+  inlen: [32, 128, 1024],
+  chunk: [16, 64, 256, 1024],
+  n: [25e4]
+});
+
+var UTF_ALPHA = 'Blåbærsyltetøy';
+var ASC_ALPHA = 'Blueberry jam';
+
+function main(conf) {
+  var encoding = conf.encoding;
+  var inLen = conf.inlen | 0;
+  var chunkLen = conf.chunk | 0;
+  var n = conf.n | 0;
+
+  var alpha;
+  var chunks = [];
+  var str = '';
+  var isBase64 = (encoding === 'base64-ascii' || encoding === 'base64-utf8');
+
+  if (encoding === 'ascii' || encoding === 'base64-ascii')
+    alpha = ASC_ALPHA;
+  else if (encoding === 'utf8' || encoding === 'base64-utf8')
+    alpha = UTF_ALPHA;
+  else
+    throw new Error('Bad encoding');
+
+  var sd = new StringDecoder(isBase64 ? 'base64' : encoding);
+
+  for (var i = 0; i < inLen; ++i) {
+    if (i > 0 && (i % chunkLen) === 0 && !isBase64) {
+      chunks.push(new Buffer(str, encoding));
+      str = '';
+    }
+    str += alpha[i % alpha.length];
+  }
+  if (str.length > 0 && !isBase64)
+    chunks.push(new Buffer(str, encoding));
+  if (isBase64) {
+    str = new Buffer(str, 'utf8').toString('base64');
+    while (str.length > 0) {
+      var len = Math.min(chunkLen, str.length);
+      chunks.push(new Buffer(str.substring(0, len), 'utf8'));
+      str = str.substring(len);
+    }
+  }
+
+  var nChunks = chunks.length;
+
+  bench.start();
+  for (var i = 0; i < n; ++i) {
+    for (var j = 0; j < nChunks; ++j)
+      sd.write(chunks[j]);
+  }
+  bench.end(n);
+}