diff --git a/include/rapidjson/document.h b/include/rapidjson/document.h index ec7f8a6..9c3d9ac 100644 --- a/include/rapidjson/document.h +++ b/include/rapidjson/document.h @@ -1247,12 +1247,12 @@ int z = a[0u].GetInt(); // This works too. //!@name String //@{ - const Ch* GetString() const { RAPIDJSON_ASSERT(IsString()); return data_.s.str; } + const Ch* GetString() const { RAPIDJSON_ASSERT(IsString()); return ((flags_ & kInlineStrFlag) ? data_.ss.str : data_.s.str); } //! Get the length of string. /*! Since rapidjson permits "\\u0000" in the json string, strlen(v.GetString()) may not equal to v.GetStringLength(). */ - SizeType GetStringLength() const { RAPIDJSON_ASSERT(IsString()); return data_.s.length; } + SizeType GetStringLength() const { RAPIDJSON_ASSERT(IsString()); return ((flags_ & kInlineStrFlag) ? (data_.ss.GetLength()) : data_.s.length); } //! Set this value as a string without copying source string. /*! This version has better performance with supplied length, and also support string containing null character. @@ -1320,7 +1320,7 @@ int z = a[0u].GetInt(); // This works too. if (!handler.StartObject()) return false; for (ConstMemberIterator m = MemberBegin(); m != MemberEnd(); ++m) { - if (!handler.String(m->name.data_.s.str, m->name.data_.s.length, (m->name.flags_ & kCopyFlag) != 0)) + if (!handler.String(m->name.GetString(), m->name.GetStringLength(), (m->name.flags_ & kCopyFlag) != 0)) return false; if (!m->value.Accept(handler)) return false; @@ -1336,7 +1336,7 @@ int z = a[0u].GetInt(); // This works too. return handler.EndArray(data_.a.size); case kStringType: - return handler.String(data_.s.str, data_.s.length, (flags_ & kCopyFlag) != 0); + return handler.String(GetString(), GetStringLength(), (flags_ & kCopyFlag) != 0); case kNumberType: if (IsInt()) return handler.Int(data_.n.i.i); @@ -1365,6 +1365,7 @@ private: kDoubleFlag = 0x4000, kStringFlag = 0x100000, kCopyFlag = 0x200000, + kInlineStrFlag = 0x400000, // Initial flags of different types. kNullFlag = kNullType, @@ -1378,6 +1379,7 @@ private: kNumberAnyFlag = kNumberType | kNumberFlag | kIntFlag | kInt64Flag | kUintFlag | kUint64Flag | kDoubleFlag, kConstStringFlag = kStringType | kStringFlag, kCopyStringFlag = kStringType | kStringFlag | kCopyFlag, + kShortStringFlag = kStringType | kStringFlag | kCopyFlag | kInlineStrFlag, kObjectFlag = kObjectType, kArrayFlag = kArrayType, @@ -1393,6 +1395,23 @@ private: unsigned hashcode; //!< reserved }; // 12 bytes in 32-bit mode, 16 bytes in 64-bit mode + // implementation detail: ShortString can represent zero-terminated strings up to MaxSize chars + // (excluding the terminating zero) and store a value to determine the length of the contained + // string in the last character str[LenPos] by storing "MaxSize - length" there. If the string + // to store has the maximal length of MaxSize then str[LenPos] will be 0 and therefore act as + // the string terminator as well. For getting the string length back from that value just use + // "MaxSize - str[LenPos]". + // This allows to store 11-chars strings in 32-bit mode and 15-chars strings in 64-bit mode + // inline (for `UTF8`-encoded strings). + struct ShortString { + enum { MaxChars = sizeof(String) / sizeof(Ch), MaxSize = MaxChars - 1, LenPos = MaxSize }; + Ch str[MaxChars]; + + inline static bool Usable(SizeType len) { return (MaxSize >= len); } + inline void SetLength(SizeType len) { str[LenPos] = (Ch)(MaxSize - len); } + inline SizeType GetLength() const { return (SizeType)(MaxSize - str[LenPos]); } + }; // at most as many bytes as "String" above => 12 bytes in 32-bit mode, 16 bytes in 64-bit mode + // By using proper binary layout, retrieval of different integer types do not need conversions. union Number { #if RAPIDJSON_ENDIAN == RAPIDJSON_LITTLEENDIAN @@ -1433,6 +1452,7 @@ private: union Data { String s; + ShortString ss; Number n; Object o; Array a; @@ -1463,11 +1483,19 @@ private: //! Initialize this value as copy string with initial data, without calling destructor. void SetStringRaw(StringRefType s, Allocator& allocator) { - flags_ = kCopyStringFlag; - data_.s.str = (Ch *)allocator.Malloc((s.length + 1) * sizeof(Ch)); - data_.s.length = s.length; - memcpy(const_cast(data_.s.str), s, s.length * sizeof(Ch)); - const_cast(data_.s.str)[s.length] = '\0'; + Ch* str = NULL; + if(ShortString::Usable(s.length)) { + flags_ = kShortStringFlag; + data_.ss.SetLength(s.length); + str = data_.ss.str; + } else { + flags_ = kCopyStringFlag; + data_.s.length = s.length; + str = (Ch *)allocator.Malloc((s.length + 1) * sizeof(Ch)); + data_.s.str = str; + } + memcpy(str, s, s.length * sizeof(Ch)); + str[s.length] = '\0'; } //! Assignment without calling destructor @@ -1480,9 +1508,16 @@ private: bool StringEqual(const GenericValue& rhs) const { RAPIDJSON_ASSERT(IsString()); RAPIDJSON_ASSERT(rhs.IsString()); - return data_.s.length == rhs.data_.s.length && - (data_.s.str == rhs.data_.s.str // fast path for constant string - || memcmp(data_.s.str, rhs.data_.s.str, sizeof(Ch) * data_.s.length) == 0); + + const SizeType len1 = GetStringLength(); + const SizeType len2 = rhs.GetStringLength(); + if(len1 != len2) { return false; } + + const Ch* const str1 = GetString(); + const Ch* const str2 = rhs.GetString(); + if(str1 == str2) { return true; } // fast path for constant string + + return (memcmp(str1, str2, sizeof(Ch) * len1) == 0); } Data data_; diff --git a/test/unittest/valuetest.cpp b/test/unittest/valuetest.cpp index e165452..7cc81dc 100644 --- a/test/unittest/valuetest.cpp +++ b/test/unittest/valuetest.cpp @@ -1084,3 +1084,23 @@ TEST(Document, CrtAllocator) { V a(kArrayType); a.PushBack(1, allocator); // Should not call destructor on uninitialized Value of newly allocated elements. } + +static void TestShortStringOptimization(const char* str) { + const rapidjson::SizeType len = (rapidjson::SizeType)strlen(str); + + rapidjson::Document doc; + rapidjson::Value val; + val.SetString(str, len, doc.GetAllocator()); + + EXPECT_EQ(val.GetStringLength(), len); + EXPECT_STREQ(val.GetString(), str); +} + +TEST(Value, AllocateShortString) { + TestShortStringOptimization(""); // edge case: empty string + TestShortStringOptimization("12345678"); // regular case for short strings: 8 chars + TestShortStringOptimization("12345678901"); // edge case: 11 chars in 32-bit mode (=> short string) + TestShortStringOptimization("123456789012"); // edge case: 12 chars in 32-bit mode (=> regular string) + TestShortStringOptimization("123456789012345"); // edge case: 15 chars in 64-bit mode (=> short string) + TestShortStringOptimization("1234567890123456"); // edge case: 16 chars in 64-bit mode (=> regular string) +}