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#ifndef CALCULATEHASH_P_H
#define CALCULATEHASH_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 <QtCore/qglobal.h>
#include <QtCore/qstring.h>

QT_BEGIN_NAMESPACE

// This is a reimplementation of V8's string hash algorithm.  It is significantly
// faster to do it here than call into V8, but it adds the maintenance burden of
// ensuring that the two hashes are identical.  We Q_ASSERT() that the two return
// the same value.  If these asserts start to fail, the hash code needs to be
// synced with V8.
namespace HashedString {
    static const int kMaxArrayIndexSize = 10;
    static const int kMaxHashCalcLength = 16383;
    static const int kNofHashBitFields = 2;
    static const int kHashShift = kNofHashBitFields;
    static const int kIsNotArrayIndexMask = 1 << 1;
    static const int kArrayIndexValueBits = 24;
    static const int kArrayIndexHashLengthShift = kArrayIndexValueBits + kNofHashBitFields;
    static const int kMaxCachedArrayIndexLength = 7;
};

template <typename schar>
uint32_t calculateHash(const schar* chars, int length) {
    if (length > HashedString::kMaxHashCalcLength) {
        // V8 trivial hash
        return (length << HashedString::kHashShift) | HashedString::kIsNotArrayIndexMask;
    }

    uint32_t raw_running_hash = 0;
    uint32_t array_index = 0;
    bool is_array_index = (0 < length && length <= HashedString::kMaxArrayIndexSize);
    bool is_first_char = true;

    int ii = 0;
    for (;is_array_index && ii < length; ++ii) {
        quint32 c = *chars++;

        raw_running_hash += c;
        raw_running_hash += (raw_running_hash << 10);
        raw_running_hash ^= (raw_running_hash >> 6);

        if (c < '0' || c > '9') {
            is_array_index = false;
        } else {
            int d = c - '0';
            if (is_first_char) {
                is_first_char = false;
                if (c == '0' && length > 1) {
                    is_array_index = false;
                    continue;
                }
            }
            if (array_index > 429496729U - ((d + 2) >> 3)) {
                is_array_index = false;
            } else {
                array_index = array_index * 10 + d;
            }
        }
    }

    for (;ii < length; ++ii) {
        raw_running_hash += *chars++;
        raw_running_hash += (raw_running_hash << 10);
        raw_running_hash ^= (raw_running_hash >> 6);
    }

    if (is_array_index) {
        array_index <<= HashedString::kHashShift;
        array_index |= length << HashedString::kArrayIndexHashLengthShift;
        return array_index;
    } else {
        raw_running_hash += (raw_running_hash << 3);
        raw_running_hash ^= (raw_running_hash >> 11);
        raw_running_hash += (raw_running_hash << 15);
        if (raw_running_hash == 0) {
            raw_running_hash = 27;
        }

        return (raw_running_hash << HashedString::kHashShift) | HashedString::kIsNotArrayIndexMask;
    }
}

QT_END_NAMESPACE

#endif // CALCULATEHASH_P_H