Remove run-time calculation of hash constants in pdfium.

fpdfsdk/src/javascript/global.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
  
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "../../include/javascript/JavaScript.h"
 #include "../../include/javascript/IJavaScript.h"
 #include "../../include/javascript/JS_Define.h"
 #include "../../include/javascript/JS_Object.h"
 #include "../../include/javascript/JS_Value.h"
 #include "../../include/javascript/JS_GlobalData.h"
 #include "../../include/javascript/global.h"
 #include "../../include/javascript/JS_EventHandler.h"
 #include "../../include/javascript/JS_Context.h"
 
 /* ---------------------------- global ---------------------------- */
 
-extern const unsigned int JSCONST_nStringHash = JS_CalcHash(VALUE_NAME_STRING,wcslen(VALUE_NAME_STRING));
-extern const unsigned int JSCONST_nNumberHash = JS_CalcHash(VALUE_NAME_NUMBER,wcslen(VALUE_NAME_NUMBER));
-extern const unsigned int JSCONST_nBoolHash = JS_CalcHash(VALUE_NAME_BOOLEAN,wcslen(VALUE_NAME_BOOLEAN));
-extern const unsigned int JSCONST_nDateHash = JS_CalcHash(VALUE_NAME_DATE,wcslen(VALUE_NAME_DATE));
-extern const unsigned int JSCONST_nObjectHash = JS_CalcHash(VALUE_NAME_OBJECT,wcslen(VALUE_NAME_OBJECT));
-extern const unsigned int JSCONST_nFXobjHash = JS_CalcHash(VALUE_NAME_FXOBJ,wcslen(VALUE_NAME_FXOBJ));
-extern const unsigned int JSCONST_nNullHash = JS_CalcHash(VALUE_NAME_NULL,wcslen(VALUE_NAME_NULL));
-extern const unsigned int JSCONST_nUndefHash = JS_CalcHash(VALUE_NAME_UNDEFINED,wcslen(VALUE_NAME_UNDEFINED));
+// Helper class to raise 1331 to the power of the length of the
+// template parameter pack.
+template <wchar_t... Ns>
+struct Pow {};
+
+template <wchar_t N>
+struct Pow<N> { static const unsigned value = 1313;
+};
+
+template <wchar_t N, wchar_t... Ns>
+struct Pow<N, Ns...> {
+  static const unsigned long long value = (1313LLU * Pow<Ns...>::value)
+    & 0xFFFFFFFF;
+};
+
+
+// Helper class for compile-time calculation of hash values in order to
+// avoid having global object initializers.
+template <wchar_t... Ns>
+struct CHash {};
+
+template <wchar_t N>
+struct CHash<N> { static const unsigned value = N;
+};
+
+template <wchar_t N, wchar_t... Ns>
+struct CHash<N, Ns...> {
+  static const unsigned value = (N * Pow<Ns...>::value + CHash<Ns...>::value)

[Tom Sepez, 2015/01/05 20:14:08]

Is there a way to avoid double recursion? We're going to be computing Pow<...>
over and over as we recurse into CHash<...>.  I see why you do this because of
ordering of paramenters vs. result.  What if we tried to add an 'accummulator'
parameter to the template to pass partial values down to the next template to
deal with this?

+    & 0xFFFFFFFF;
+};
+
+extern const unsigned int JSCONST_nStringHash =
+  CHash<'s','t','r','i','n','g'>::value;
+extern const unsigned int JSCONST_nNumberHash =
+  CHash<'n','u','m','b','e','r'>::value;
+extern const unsigned int JSCONST_nBoolHash =
+  CHash<'b','o','o','l','e','a','n'>::value;
+extern const unsigned int JSCONST_nDateHash =
+  CHash<'d','a','t','e'>::value;
+extern const unsigned int JSCONST_nObjectHash =
+  CHash<'o','b','j','e','c','t'>::value;
+extern const unsigned int JSCONST_nFXobjHash =
+  CHash<'f','x','o','b','j'>::value;
+extern const unsigned int JSCONST_nNullHash =
+  CHash<'n','u','l','l'>::value;
+extern const unsigned int JSCONST_nUndefHash =
+  CHash<'u','n','d','e','f','i','n','e','d'>::value;
+
+#ifdef _DEBUG
+class HashVerify
+{
+public:
+  HashVerify();
+} g_hashVerify;
+
+HashVerify::HashVerify()
+{
+  ASSERT(JSCONST_nStringHash ==
+    JS_CalcHash(VALUE_NAME_STRING,wcslen(VALUE_NAME_STRING)));
+  ASSERT(JSCONST_nNumberHash ==
+    JS_CalcHash(VALUE_NAME_NUMBER,wcslen(VALUE_NAME_NUMBER)));
+  ASSERT(JSCONST_nBoolHash ==
+    JS_CalcHash(VALUE_NAME_BOOLEAN,wcslen(VALUE_NAME_BOOLEAN)));
+  ASSERT(JSCONST_nDateHash ==
+    JS_CalcHash(VALUE_NAME_DATE,wcslen(VALUE_NAME_DATE)));
+  ASSERT(JSCONST_nObjectHash ==
+    JS_CalcHash(VALUE_NAME_OBJECT,wcslen(VALUE_NAME_OBJECT)));
+  ASSERT(JSCONST_nFXobjHash ==
+    JS_CalcHash(VALUE_NAME_FXOBJ,wcslen(VALUE_NAME_FXOBJ)));
+  ASSERT(JSCONST_nNullHash ==
+    JS_CalcHash(VALUE_NAME_NULL,wcslen(VALUE_NAME_NULL)));
+  ASSERT(JSCONST_nUndefHash ==
+    JS_CalcHash(VALUE_NAME_UNDEFINED,wcslen(VALUE_NAME_UNDEFINED)));
+}
+#endif
+
 
 BEGIN_JS_STATIC_CONST(CJS_Global)
 END_JS_STATIC_CONST()
 
 BEGIN_JS_STATIC_PROP(CJS_Global)
 END_JS_STATIC_PROP()
 
 BEGIN_JS_STATIC_METHOD(CJS_Global)
         JS_STATIC_METHOD_ENTRY(setPersistent, 2)
 END_JS_STATIC_METHOD()
@@ skipping 513 matching lines @@
                 }
                 break;
         default:
                 return FALSE;
         }       
 
         m_mapGlobal.SetAt(propname, (FX_LPVOID)pNewData);
 
         return TRUE;
 }