path: root/src/qjson_p.h

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#ifndef QJSON_P_H
#define QJSON_P_H

//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//

#include <qjsonglobal.h>
#include <qjsonobject.h>
#include <qjsonvalue.h>
#include <qjsonarray.h>
#include <qbasicatomic.h>
#include <qstring.h>
#include <qendian.h>

/*
  This defines a binary data structure for Json data. The data structure is optimised for fast reading and minimum allocations.
  The whole data structure can be mmap'ed and used directly.

  In most cases the binary structure is not as space efficient as a utf8 encoded text representation, but much faster to access.

  The size requirements are:

  String: 16 bytes header + 2*(string.length())

  Values: 4 bytes + size of data (size can be 0 for some data)
    bool: 0 bytes
    number: 8 bytes
    string: 4 + 2*length of string
    array: size of array
    object: size of object
  Array: 12 bytes + 4*length + size of Value data
  Object: 12 bytes + 8*length + size of Key Strings + size of Value data

  For an example such as

    {                                           // object: 12 + 5*8                = 52
         "firstName": "John",                   // key 4+12, value 8          = 24
         "lastName" : "Smith",                  // key 4+8, value 8         = 20
         "age"      : 25,                       // key 4+4, value 0             = 8
         "address"  :                           // key 4+8, object below = 154
         {                                      // object: 12 + 4*8
             "streetAddress": "21 2nd Street",  // key 4+16, value 16
             "city"         : "New York",       // key 4+4, value 12
             "state"        : "NY",             // key 4+8, value 4
             "postalCode"   : "10021"           // key 4+12, value 8
         },                                     // object total: 148
         "phoneNumber":                         // key: 4+12, value array below = 208
         [                                      // array: 12 + 2*4 + values below = 176
             {                                  // object 12 + 2*8
               "type"  : "home",                // key 4+4, value 8
               "number": "212 555-1234"         // key 4+8, value 16
             },                                 // object total: 84
             {                                  // object 12 + 2*8
               "type"  : "fax",                 // key 4+4, value 8
               "number": "646 555-4567"         // key 4+8, value 16
             }                                  // object total: 84
         ]                                      // array total: 248
    }                                           // great total:                       416 bytes

    The uncompressed text file used roughly 500 bytes, so we end up using about the same space
    as the text representation.
*/
namespace QtJson
{

typedef uint offset;
struct Array;
struct Object;
struct Value;
struct Entry;

static inline int alignedSize(int size) { return (size + 3) & ~3; }

static inline bool useCompressed(const QString &s)
{
    if (s.length() >= 0x8000)
        return false;
    const ushort *uc = (const ushort *)s.constData();
    const ushort *e = uc + s.length();
    while (uc < e) {
        if (*uc > 0xff)
            return false;
        ++uc;
    }
    return true;
}

static inline int qStringSize(const QString &string, bool compress)
{
    int l = 2 + string.length();
    if (!compress)
        l *= 2;
    return alignedSize(l);
}


// returns INT_MAX if it can't compress it into 28 bits
static inline int compressedNumber(double d)
{
    // this relies on details of how ieee floats are represented
    const int exponent_off = 52;
    const quint64 fraction_mask = 0x000fffffffffffffull;
    const quint64 exponent_mask = 0x7ff0000000000000ull;

    union {
        quint64 val;
        double dbl;
    };
    dbl = d;
    int exp = (int)((val & exponent_mask) >> exponent_off) - 1023;
    if (exp < 0 || exp > 25)
        return INT_MAX;

    quint64 non_int = val & (fraction_mask >> exp);
    if (non_int)
        return INT_MAX;

    bool neg = (val >> 63);
    val &= fraction_mask;
    val |= ((quint64)1 << 52);
    int res = (int)(val >> (52 - exp));
    return neg ? -res : res;
}

struct Latin1String;

struct String
{
    String(const char *data) { d = (Data *)data; }

    struct Data {
        int length;
        ushort utf16[1];
    };

    Data *d;

    inline String &operator=(const QString &str)
    {
        d->length = str.length();
        memcpy(d->utf16, str.unicode(), d->length*sizeof(ushort));
        if (d->length & 1)
            d->utf16[d->length] = 0;
        return *this;
    }

    bool operator ==(const QString &str) {
        int slen = str.length();
        const ushort *s = (const ushort *)str.constData();
        if (slen != d->length)
            return false;
        int l = d->length;
        const ushort *a = d->utf16;
        const ushort *b = s;
        while (l-- && *a == *b)
            a++,b++;
        return (l == -1);
    }
    bool operator !=(const QString &str) {
        return !operator ==(str);
    }
};

struct Latin1String
{
    Latin1String(const char *data) { d = (Data *)data; }

    struct Data {
        short length;
        uchar latin1[1];
    };
    Data *d;

    inline Latin1String &operator=(const QString &str)
    {
        d->length = str.length();
        uchar *l = d->latin1;
        const ushort *uc = (const ushort *)str.unicode();
        for (int i = 0; i < str.length(); ++i)
            *l++ = uc[i];
        while ((quintptr)l & 0x3)
            *l++ = 0;
        return *this;
    }

    bool operator ==(const QString &str) {
        int slen = str.length();
        const ushort *s = (const ushort *)str.constData();
        if (slen != d->length)
            return false;
        int l = d->length;
        const uchar *a = d->latin1;
        const ushort *b = s;
        while (l-- && *a == *b)
            a++,b++;
        return (l == -1);
    }
    bool operator !=(const QString &str) {
        return !operator ==(str);
    }
};


static inline void copyString(char *dest, const QString &str, bool compress)
{
    if (compress) {
        Latin1String string(dest);
        string = str;
    } else {
        String string(dest);
        string = str;
    }
}



struct Base
{
    uint size;
    uint length : 31;
    uint is_object : 1; // object or Array
    offset tableOffset;
    // content follows here

    inline bool isObject() const { return is_object; }
    inline bool isArray() const { return !is_object; }

    inline offset *table() const { return (offset *) (((char *) this) + tableOffset); }

    int reserveSpace(uint dataSize, int posInTable, uint numItems);
    void removeItems(int pos, int numItems);
};

struct Object : public Base
{

    Entry *entryAt(int i) const {
        return reinterpret_cast<Entry *>(((char *)this) + table()[i]);
    }
    int indexOf(const QString &key);
    int insertKey(const QString &key);

    bool isValid() const;
};


struct Array : public Base
{
    inline Value at(int i) const;
    inline Value &operator [](int i);

    bool isValid() const;
};


struct Value
{
    // unfortunately some compilers can't handle mixed types in bitfields.
    // this works around the problem
    union {
        struct {
            int unused : 5;
            int int_val : 27;
        };
        struct {
            uint type : 3;
            uint latinOrIntValue : 1;
            uint latinKey : 1;
            uint val : 27;
        };
    };


    inline char *data(const Base *b) const { return ((char *)b) + val; }
    int usedStorage(const Base *b) const;

    bool toBoolean() const;
    double toNumber(const Base *b) const;
    int toInt() const;
    QString toString(const Base *b) const;
    String asString(const Base *b) const;
    Latin1String asLatin1String(const Base *b) const;
    Base *objectOrArray(const Base *b) const;

    bool isValid(const Base *b) const;
};

inline Value Array::at(int i) const
{
    return * (Value *) (((char *) this) + tableOffset + i*sizeof(Value));
}

inline Value &Array::operator [](int i)
{
    return * (Value *) (((char *) this) + tableOffset + i*sizeof(Value));
}



struct Entry {
    Value value;
    ushort *keyData() const { return (ushort *)((const char *)this + sizeof(Entry) + sizeof(int)); }
    uchar *latin1KeyData() const { return (uchar *)((const char *)this + sizeof(Entry) + sizeof(ushort)); }
    // key
    // value data follows key

    int size() const {
        int s = sizeof(Entry);
        if (value.latinKey)
            s += sizeof(ushort) + *(ushort *) ((const char *)this + sizeof(Entry));
        else
            s += sizeof(uint) + *(int *) ((const char *)this + sizeof(Entry));
        return alignedSize(s);
    }

    int usedStorage(Base *b) const {
        return size() + value.usedStorage(b);
    }

    String shallowKey() const
    {
        Q_ASSERT(!value.latinKey);
        return String((const char *)this + sizeof(Entry));
    }
    Latin1String shallowLatin1Key() const
    {
        Q_ASSERT(value.latinKey);
        return Latin1String((const char *)this + sizeof(Entry));
    }
    QString key() const
    {
        if (value.latinKey) {
            int length = *(ushort *) ((const char *)this + sizeof(Entry));
            return QString::fromLatin1((const char *)latin1KeyData(), length);
        }
        int length = *(int *) ((const char *)this + sizeof(Entry));
        return QString((const QChar *)keyData(), length);
    }

    bool matchesKey(const QString &key);
};

struct Header {
    uint tag; // 'qbjs'
    uint version; // 1
    Base *root() { return (Base *)(this + 1); }
};


inline bool Value::toBoolean() const
{
    Q_ASSERT(type == BooleanValue);
    return val != 0;
}

inline double Value::toNumber(const Base *b) const
{
    Q_ASSERT(type == NumberValue);
    if (latinOrIntValue)
        return int_val;

    union {
        char raw[sizeof(double)];
        double d;
    };
    memcpy(raw, ((char *)b + val), sizeof(double));
    return d;
}

inline int Value::toInt() const
{
    Q_ASSERT(type == NumberValue && latinOrIntValue);
    return int_val;
}

inline QString Value::toString(const Base *b) const
{
    char *d = data(b);
    if (latinOrIntValue) {
        int l = *(ushort *)d;
        return QString::fromLatin1(d + sizeof(ushort), l);
    }
    int l = *(int *)d;
    const QChar *c = (const QChar *)(d + sizeof(int));
    return QString(c, l);
}

inline String Value::asString(const Base *b) const
{
    Q_ASSERT(type == StringValue && !latinOrIntValue);
    return String(data(b));
}

inline Latin1String Value::asLatin1String(const Base *b) const
{
    Q_ASSERT(type == StringValue && latinOrIntValue);
    return Latin1String(data(b));
}

inline Base *Value::objectOrArray(const Base *b) const
{
    Q_ASSERT(type == ArrayValue || type == ObjectValue);
    return reinterpret_cast<Base *>(data(b));
}

struct Data {
    enum Validation {
        Unchecked,
        Validated,
        Invalid
    };

    inline Data(char *raw, int a)
        : alloc(a), compactionCounter(0), valid(Unchecked), rawData(raw)
    {
        ref.store(0);
    }
    inline Data(int reserved, ValueType valueType)
        : compactionCounter(0), valid(Validated), rawData(0)
    {
        ref.store(0);

        alloc = sizeof(Header) + sizeof(Base) + reserved + sizeof(offset);
        header = (Header *)malloc(alloc);
        header->tag = QBJS_Tag;
        header->version = 1;
        Base *b = header->root();
        b->size = sizeof(Base);
        b->is_object = (valueType == ObjectValue);
        b->tableOffset = sizeof(Base);
        b->length = 0;
    }
    inline ~Data()
    { free(rawData); }

    QBasicAtomicInt ref;
    int alloc;
    int compactionCounter;
    Validation valid;
    union {
        char *rawData;
        Header *header;
    };

    uint offsetOf(const void *ptr) const { return ((char *)ptr - rawData); }

    Object *object(int offset) const { return reinterpret_cast<Object *>(rawData + offset); }
    Entry *entry(int offset) const { return reinterpret_cast<Entry *>(rawData + offset); }
    Value *value(int offset) const { return reinterpret_cast<Value *>(rawData + offset); }
    Array *array(int offset) const { return reinterpret_cast<Array *>(rawData + offset); }


    JsonObject toObject(Object *o) const
    {
        return JsonObject(const_cast<Data *>(this), o);
    }

    JsonArray toArray(Array *a) const
    {
        return JsonArray(const_cast<Data *>(this), a);
    }

    Data *detach(Base *b, int reserve = 0)
    {
        int size = sizeof(Header) + b->size + reserve;
        char *raw = (char *)malloc(size);
        memcpy(raw + sizeof(Header), b, b->size);
        Header *h = (Header *)raw;
        h->tag = QBJS_Tag;
        h->version = 1;
        Data *d = new Data(raw, size);
        d->compactionCounter = compactionCounter;
        return d;
    }

    void compact();
    void validate();
};

}

#endif // QJSON_P_H