diff --git a/courgette/crc.cc b/courgette/crc.cc
new file mode 100644
index 0000000..28a0f9c
--- /dev/null
+++ b/courgette/crc.cc
@@ -0,0 +1,34 @@
+// Copyright (c) 2011 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 "courgette/crc.h"
+
+#ifdef COURGETTE_USE_CRC_LIB
+#  include "zlib.h"
+#else
+extern "C" {
+#  include "third_party/lzma_sdk/7zCrc.h"
+}
+#endif
+
+#include "base/basictypes.h"
+
+namespace courgette {
+
+uint32 CalculateCrc(const uint8* buffer, size_t size) {
+  uint32 crc;
+
+#ifdef COURGETTE_USE_CRC_LIB
+  // Calculate Crc by calling CRC method in zlib
+  crc = crc32(0, buffer, size);
+#else
+  // Calculate Crc by calling CRC method in LZMA SDK
+  CrcGenerateTable();
+  crc = CrcCalc(buffer, size);
+#endif
+
+  return ~crc;
+}
+
+}  // namespace