Mime sniffer: reduce table from 256 bytes to 4

net/base/mime_sniffer_perftest.cc

Index: net/base/mime_sniffer_perftest.cc
diff --git a/net/base/mime_sniffer_perftest.cc b/net/base/mime_sniffer_perftest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ccb67c80acfd49133700185d075d1578a4d1d04f
--- /dev/null
+++ b/net/base/mime_sniffer_perftest.cc
@@ -0,0 +1,99 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/base/mime_sniffer.h"
+
+#include <vector>
+
+#include "base/logging.h"
+#include "base/timer/elapsed_timer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace net {
+namespace {
+
+// This text is supposed to be representative of a plain text file the browser
+// might encounter, including a variation in line lengths and blank
+// lines. CRLF is used as the line-terminator to make it slightly more
+// difficult. It is roughly 1KB.
+const char kRepresentativePlainText[] =
+    "The Tragedie of Hamlet\r\n"
+    "\r\n"
+    "Actus Primus. Scoena Prima.\r\n"
+    "\r\n"
+    "Enter Barnardo and Francisco two Centinels.\r\n"
+    "\r\n"
+    "  Barnardo. Who's there?\r\n"
+    "  Fran. Nay answer me: Stand & vnfold\r\n"
+    "your selfe\r\n"
+    "\r\n"
+    "   Bar. Long liue the King\r\n"
+    "\r\n"
+    "   Fran. Barnardo?\r\n"
+    "  Bar. He\r\n"
+    "\r\n"
+    "   Fran. You come most carefully vpon your houre\r\n"
+    "\r\n"
+    "   Bar. 'Tis now strook twelue, get thee to bed Francisco\r\n"
+    "\r\n"
+    "   Fran. For this releefe much thankes: 'Tis bitter cold,\r\n"
+    "And I am sicke at heart\r\n"
+    "\r\n"
+    "   Barn. Haue you had quiet Guard?\r\n"
+    "  Fran. Not a Mouse stirring\r\n"
+    "\r\n"
+    "   Barn. Well, goodnight. If you do meet Horatio and\r\n"
+    "Marcellus, the Riuals of my Watch, bid them make hast.\r\n"
+    "Enter Horatio and Marcellus.\r\n"
+    "\r\n"
+    "  Fran. I thinke I heare them. Stand: who's there?\r\n"
+    "  Hor. Friends to this ground\r\n"
+    "\r\n"
+    "   Mar. And Leige-men to the Dane\r\n"
+    "\r\n"
+    "   Fran. Giue you good night\r\n"
+    "\r\n"
+    "   Mar. O farwel honest Soldier, who hath relieu'd you?\r\n"
+    "  Fra. Barnardo ha's my place: giue you goodnight.\r\n"
+    "\r\n"
+    "Exit Fran.\r\n"
+    "\r\n"
+    "  Mar. Holla Barnardo\r\n"
+    "\r\n"
+    "   Bar. Say, what is Horatio there?\r\n"
+    "  Hor. A peece of him\r\n"
+    "\r\n"
+    "   Bar. Welcome Horatio, welcome good Marcellus\r\n"
+    "\r\n";
+
+void RunLooksLikeBinary(const std::string& plaintext, size_t iterations) {
+  bool looks_like_binary = false;
+  for (size_t i = 0; i < iterations; ++i) {
+    if (LooksLikeBinary(&plaintext[0], plaintext.size()))
+      looks_like_binary = true;
+  }
+  CHECK(!looks_like_binary);
+}
+
+TEST(MimeSnifferTest, PlainTextPerfTest) {
+  // Android systems have a relatively small CPU cache (512KB to 2MB).
+  // It is better if the test data fits in cache so that we are not just
+  // testing bus bandwidth.
+  const size_t kTargetSize = 1 << 18;  // 256KB
+  const size_t kWarmupIterations = 16;
+  const size_t kMeasuredIterations = 1 << 15;
+  std::string plaintext = kRepresentativePlainText;
+  plaintext.reserve(kTargetSize + plaintext.size() % kTargetSize);

[asanka, 2015/05/12 19:20:41]

ISTM this should be:

plaintext.reserve(plaintext.size() * (1 << base::bits::Log2Ceiling(kTargetSize /
plaintext.size())));

[Adam Rice, 2015/05/18 01:02:56]

Good catch! Thanks.

+  while (plaintext.size() < kTargetSize)
+    plaintext += plaintext;
+  RunLooksLikeBinary(plaintext, kWarmupIterations);
+  base::ElapsedTimer elapsed_timer;
+  RunLooksLikeBinary(plaintext, kMeasuredIterations);
+  LOG(INFO) << (elapsed_timer.Elapsed().InMicroseconds() * 1000 * 1024 /
+                (static_cast<int64>(plaintext.size()) * kMeasuredIterations))
+            << "ns per KB";
+}
+
+}  // namespace net
+}  // namespace