Remove run-time calculation of hash constants in pdfium.

fpdfsdk/src/javascript/global.cpp

Index: fpdfsdk/src/javascript/global.cpp
diff --git a/fpdfsdk/src/javascript/global.cpp b/fpdfsdk/src/javascript/global.cpp
index 04f9ef9da37938666db05320615de5e1b4bbad3b..fb9c3a57b36781c3ab048ef6cf38b50388b0b5fa 100644
--- a/fpdfsdk/src/javascript/global.cpp
+++ b/fpdfsdk/src/javascript/global.cpp
@@ -16,14 +16,82 @@
 
 /* ---------------------------- 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()