Use 12-16 bytes less per string

Don't store a full QStringData, but simply
the length of the string.

Change-Id: I8b2b5a6eb7f065f2de6907955806340f5d99c0e8
Reviewed-by: Simons Kevin <kevin.simons@nokia.com>

4 files changed, 57 insertions, 33 deletions

diff --git a/src/qjson_p.h b/src/qjson_p.h
index 491a409..e016493 100644
--- a/src/qjson_p.h
+++ b/src/qjson_p.h
@@ -66,19 +66,43 @@ static inline int alignedSize(int size) { return (size + 7) & ~7; }
 
 static inline int qStringSize(const QString &string)
 {
-    return sizeof(QStringData) + sizeof(ushort)*string.length();
+    return (sizeof(ushort)*string.length() + 3) & ~3;
 }
 
-static inline void createConstString(void *dest, const QString &s)
+struct QStackString
 {
-    QStringData *data = static_cast<QStringData *>(dest);
-    data->ref.atomic.store(-1);
-    data->size = s.length();
-    data->alloc = 0;
-    data->capacityReserved = false;
-    data->offset = 0;
-    memcpy((data + 1), s.constData(), sizeof(ushort)*s.length());
-}
+    QStackString(const ushort *utf16, int length)
+        : length(length), utf16(utf16) {}
+    int length;
+    const ushort *utf16;
+
+    inline bool equals(const ushort *s, int slen) const
+    {
+        if (slen != length)
+            return false;
+        int l = length;
+        const ushort *a = utf16;
+        const ushort *b = s;
+        while (l-- && *a == *b)
+            a++,b++;
+        return (l == -1);
+    }
+
+    bool operator ==(const QString &str) {
+        return equals((const ushort *)str.constData(), str.length());
+    }
+    bool operator !=(const QString &str) {
+        return !equals((const ushort *)str.constData(), str.length());
+    }
+    bool operator ==(const QStackString &str) {
+        return equals(str.utf16, str.length);
+    }
+    bool operator !=(const QStackString &str) {
+        return !equals(str.utf16, str.length);
+    }
+};
+
+
 
 struct Value
 {
@@ -91,8 +115,8 @@ struct Value
     bool toBoolean() const;
     double toNumber() const;
     int toInt() const;
-    QString shallowString() const;
-    QString string() const;
+    QString toString() const;
+    QStackString shallowString() const;
     Array *array() const;
     Object *object() const;
 
@@ -112,7 +136,8 @@ struct Value
     static inline Value *fromString(const QString &string) {
         Value *v = alloc(sizeof(Value) + qStringSize(string));
         v->type = StringValue;
-        createConstString(v->data(), string);
+        v->val = string.length();
+        memcpy(v->data(), string.constData(), sizeof(ushort)*string.length());
         return v;
     }
     static inline Value *fromArray(const Array *a);
@@ -123,15 +148,15 @@ struct Value
 struct Entry {
     uint size;
     offset valueOffset;
-    QStringData keyString;
+    uint keyLength;
+    ushort *keyData() const { return (ushort *)(this + 1); }
+    // keydata
     // value data follows key data
 
-    QString shallowKey() const { return *reinterpret_cast<const QConstStringData<1> *>(&keyString); }
+    QStackString shallowKey() const { return QStackString(keyData(), keyLength); }
     QString key() const
     {
-        QString str = shallowKey();
-        str.detach();
-        return str;
+        return QString((const QChar *)keyData(), keyLength);
     }
     Value *value() const {
         return reinterpret_cast<Value *>(((char *)this) + valueOffset);
@@ -222,18 +247,16 @@ inline int Value::toInt() const
     return (int)*(double *)((char *)(this+1));
 }
 
-inline QString Value::shallowString() const
+inline QString Value::toString() const
 {
-    Q_ASSERT(type == StringValue);
-    return *reinterpret_cast<const QConstStringData<1> *>((char *)(this+1));
+    return QString((const QChar *)data(), val);
 }
 
-inline QString Value::string() const
+inline QStackString Value::shallowString() const
 {
-    QString str = shallowString();
-    str.detach();
-    return str;
+    return QStackString((ushort *)data(), val);
 }
+
 inline Array *Value::array() const
 {
     Q_ASSERT(type == ArrayValue);
diff --git a/src/qjsonobject.cpp b/src/qjsonobject.cpp
index 79af761..da386b8 100644
--- a/src/qjsonobject.cpp
+++ b/src/qjsonobject.cpp
@@ -140,7 +140,7 @@ void JsonObject::insert(const QString &key, const JsonValue &value)
 
     int valueSize = v ? v->size : sizeof(Value);
 
-    int valueOffset = sizeof(Entry) + sizeof(QStringData) + key.length()*sizeof(ushort);
+    int valueOffset = sizeof(Entry) + qStringSize(key);
     int requiredSize = valueOffset + valueSize;
 
     detach(requiredSize + sizeof(offset)); // offset for the new index entry
@@ -155,7 +155,8 @@ void JsonObject::insert(const QString &key, const JsonValue &value)
     o->reserveSpace(requiredSize, pos, 1);
     Entry *e = o->entryAt(pos);
     e->size = requiredSize;
-    createConstString(&e->keyString, key);
+    e->keyLength = key.length();
+    memcpy(e->keyData(), key.constData(), sizeof(ushort)*key.length());
     e->valueOffset = valueOffset;
     if (v) {
         memcpy(e->value(), v, v->size);
diff --git a/src/qjsonvalue.cpp b/src/qjsonvalue.cpp
index 2dc6008..0241482 100644
--- a/src/qjsonvalue.cpp
+++ b/src/qjsonvalue.cpp
@@ -144,7 +144,7 @@ QVariant JsonValue::toVariant() const
     case NumberValue:
         return v->toNumber();
     case StringValue:
-        return v->string();
+        return v->toString();
     case ArrayValue:
         return JsonArray(d, v->array()).toVariantList();
     case ObjectValue:
@@ -236,7 +236,7 @@ QString JsonValue::toString() const
 
     if (v->type != StringValue)
         return QString();
-    return v->string();
+    return v->toString();
 }
 
 JsonArray JsonValue::toArray() const
diff --git a/src/qjsonwriter.cpp b/src/qjsonwriter.cpp
index 133403d..3ebc192 100644
--- a/src/qjsonwriter.cpp
+++ b/src/qjsonwriter.cpp
@@ -26,16 +26,16 @@ static inline uchar hexdig(uint u)
     return (u < 0xa ? '0' + u : 'a' + u - 0xa);
 }
 
-static QByteArray escapedString(const QString &s)
+static QByteArray escapedString(const QStackString &s)
 {
     const uchar replacement = '?';
-    QByteArray ba(s.length(), Qt::Uninitialized);
+    QByteArray ba(s.length, Qt::Uninitialized);
 
     uchar *cursor = (uchar *)ba.data();
     const uchar *ba_end = cursor + ba.length();
 
-    const QChar *ch = s.constData();
-    const QChar *end = ch + s.length();
+    const QChar *ch = (const QChar *)s.utf16;
+    const QChar *end = ch + s.length;
 
     int surrogate_high = -1;