path: root/src/qml/qml/ftw/qhashedstring.cpp

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#include "qhashedstring_p.h"

inline quint32 stringHash(const QChar* data, int length)
{
    return QV4::String::createHashValue(data, length);
}

inline quint32 stringHash(const char *data, int length)
{
    return QV4::String::createHashValue(data, length);
}

void QHashedString::computeHash() const
{
    m_hash = stringHash(constData(), length());
}

void QHashedStringRef::computeHash() const
{
    m_hash = stringHash(m_data, m_length);
}

void QHashedCStringRef::computeHash() const
{
    m_hash = stringHash(m_data, m_length);
}

/*
    A QHash has initially around pow(2, MinNumBits) buckets. For
    example, if MinNumBits is 4, it has 17 buckets.
*/
const int MinNumBits = 4;

/*
    The prime_deltas array is a table of selected prime values, even
    though it doesn't look like one. The primes we are using are 1,
    2, 5, 11, 17, 37, 67, 131, 257, ..., i.e. primes in the immediate
    surrounding of a power of two.

    The primeForNumBits() function returns the prime associated to a
    power of two. For example, primeForNumBits(8) returns 257.
*/

static const uchar prime_deltas[] = {
    0,  0,  1,  3,  1,  5,  3,  3,  1,  9,  7,  5,  3,  9, 25,  3,
    1, 21,  3, 21,  7, 15,  9,  5,  3, 29, 15,  0,  0,  0,  0,  0
};

static inline int primeForNumBits(int numBits)
{
    return (1 << numBits) + prime_deltas[numBits];
}

void QStringHashData::rehashToSize(int size)
{
    short bits = qMax(MinNumBits, (int)numBits);
    while (primeForNumBits(bits) < size) bits++;

    if (bits > numBits)
        rehashToBits(bits);
}

void QStringHashData::rehashToBits(short bits)
{
    numBits = qMax(MinNumBits, (int)bits);

    int nb = primeForNumBits(numBits);
    if (nb == numBuckets && buckets)
        return;

#ifdef QSTRINGHASH_LINK_DEBUG
    if (linkCount)
        qFatal("QStringHash: Illegal attempt to rehash a linked hash.");
#endif

    QStringHashNode **newBuckets = new QStringHashNode *[nb];
    ::memset(newBuckets, 0, sizeof(QStringHashNode *) * nb);

    // Preserve the existing order within buckets so that items with the
    // same key will retain the same find/findNext order
    for (int i = 0; i < numBuckets; ++i) {
        QStringHashNode *bucket = buckets[i];
        if (bucket)
            rehashNode(newBuckets, nb, bucket);
    }

    delete [] buckets;
    buckets = newBuckets;
    numBuckets = nb;
}

void QStringHashData::rehashNode(QStringHashNode **newBuckets, int nb, QStringHashNode *node)
{
    QStringHashNode *next = node->next.data();
    if (next)
        rehashNode(newBuckets, nb, next);

    int bucket = node->hash % nb;
    node->next = newBuckets[bucket];
    newBuckets[bucket] = node;
}

// Copy of QString's qMemCompare
bool QHashedString::compare(const QChar *lhs, const QChar *rhs, int length)
{
    Q_ASSERT(lhs && rhs);
    const quint16 *a = (const quint16 *)lhs;
    const quint16 *b = (const quint16 *)rhs;

    if (a == b || !length)
        return true;

    union {
        const quint16 *w;
        const quint32 *d;
        quintptr value;
    } sa, sb;
    sa.w = a;
    sb.w = b;

    // check alignment
    if ((sa.value & 2) == (sb.value & 2)) {
        // both addresses have the same alignment
        if (sa.value & 2) {
            // both addresses are not aligned to 4-bytes boundaries
            // compare the first character
            if (*sa.w != *sb.w)
                return false;
            --length;
            ++sa.w;
            ++sb.w;

            // now both addresses are 4-bytes aligned
        }

        // both addresses are 4-bytes aligned
        // do a fast 32-bit comparison
        const quint32 *e = sa.d + (length >> 1);
        for ( ; sa.d != e; ++sa.d, ++sb.d) {
            if (*sa.d != *sb.d)
                return false;
        }

        // do we have a tail?
        return (length & 1) ? *sa.w == *sb.w : true;
    } else {
        // one of the addresses isn't 4-byte aligned but the other is
        const quint16 *e = sa.w + length;
        for ( ; sa.w != e; ++sa.w, ++sb.w) {
            if (*sa.w != *sb.w)
                return false;
        }
    }
    return true;
}

QHashedStringRef QHashedStringRef::mid(int offset, int length) const
{
    Q_ASSERT(offset < m_length);
    return QHashedStringRef(m_data + offset, 
                            (length == -1 || (offset + length) > m_length)?(m_length - offset):length);
}

bool QHashedStringRef::endsWith(const QString &s) const
{
    return s.length() < m_length && 
           QHashedString::compare(s.constData(), m_data + m_length - s.length(), s.length());
}

bool QHashedStringRef::startsWith(const QString &s) const
{
    return s.length() < m_length && 
           QHashedString::compare(s.constData(), m_data, s.length());
}

static int findChar(const QChar *str, int len, QChar ch, int from)
{
    const ushort *s = (const ushort *)str;
    ushort c = ch.unicode();
    if (from < 0)
        from = qMax(from + len, 0);
    if (from < len) {
        const ushort *n = s + from - 1;
        const ushort *e = s + len;
        while (++n != e)
            if (*n == c)
                return  n - s;
    }
    return -1;
}

int QHashedStringRef::indexOf(const QChar &c, int from) const
{
    return findChar(m_data, m_length, c, from);
}

QString QHashedStringRef::toString() const
{
    if (m_length == 0)
        return QString();
    return QString(m_data, m_length);
}

QString QHashedCStringRef::toUtf16() const
{
    if (m_length == 0)
        return QString();

    QString rv;
    rv.resize(m_length);
    writeUtf16((quint16*)rv.data());
    return rv;
}