qbytearraymatcher.cpp

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#include "qbytearraymatcher.h"

#include <limits.h>

QT_BEGIN_NAMESPACE

static inline void bm_init_skiptable(const uchar *cc, int len, uchar *skiptable)
{
    int l = qMin(len, 255);
    memset(skiptable, l, 256*sizeof(uchar));
    cc += len - l;
    while (l--)
        skiptable[*cc++] = l;
}

static inline int bm_find(const uchar *cc, int l, int index, const uchar *puc, uint pl,
                          const uchar *skiptable)
{
    if (pl == 0)
        return index > l ? -1 : index;
    const uint pl_minus_one = pl - 1;

    register const uchar *current = cc + index + pl_minus_one;
    const uchar *end = cc + l;
    while (current < end) {
        uint skip = skiptable[*current];
        if (!skip) {
            // possible match
            while (skip < pl) {
                if (*(current - skip) != puc[pl_minus_one - skip])
                    break;
                skip++;
            }
            if (skip > pl_minus_one) // we have a match
                return (current - cc) - skip + 1;

            // in case we don't have a match we are a bit inefficient as we only skip by one
            // when we have the non matching char in the string.
            if (skiptable[*(current - skip)] == pl)
                skip = pl - skip;
            else
                skip = 1;
        }
        if (current > end - skip)
            break;
        current += skip;
    }
    return -1; // not found
}

QByteArrayMatcher::QByteArrayMatcher()
    : d(0)
{
    p.p = 0;
    p.l = 0;
    qMemSet(p.q_skiptable, 0, sizeof(p.q_skiptable));
}

QByteArrayMatcher::QByteArrayMatcher(const char *pattern, int length)
    : d(0)
{
    p.p = reinterpret_cast<const uchar *>(pattern);
    p.l = length;
    bm_init_skiptable(p.p, p.l, p.q_skiptable);
}

QByteArrayMatcher::QByteArrayMatcher(const QByteArray &pattern)
    : d(0), q_pattern(pattern)
{
    p.p = reinterpret_cast<const uchar *>(pattern.constData());
    p.l = pattern.size();
    bm_init_skiptable(p.p, p.l, p.q_skiptable);
}

QByteArrayMatcher::QByteArrayMatcher(const QByteArrayMatcher &other)
    : d(0)
{
    operator=(other);
}

QByteArrayMatcher::~QByteArrayMatcher()
{
}

QByteArrayMatcher &QByteArrayMatcher::operator=(const QByteArrayMatcher &other)
{
    q_pattern = other.q_pattern;
    memcpy(&p, &other.p, sizeof(p));
    return *this;
}

void QByteArrayMatcher::setPattern(const QByteArray &pattern)
{
    q_pattern = pattern;
    p.p = reinterpret_cast<const uchar *>(pattern.constData());
    p.l = pattern.size();
    bm_init_skiptable(p.p, p.l, p.q_skiptable);
}

int QByteArrayMatcher::indexIn(const QByteArray &ba, int from) const
{
    if (from < 0)
        from = 0;
    return bm_find(reinterpret_cast<const uchar *>(ba.constData()), ba.size(), from,
                   p.p, p.l, p.q_skiptable);
}

int QByteArrayMatcher::indexIn(const char *str, int len, int from) const
{
    if (from < 0)
        from = 0;
    return bm_find(reinterpret_cast<const uchar *>(str), len, from,
                   p.p, p.l, p.q_skiptable);
}

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

static int qFindByteArrayBoyerMoore(
    const char *haystack, int haystackLen, int haystackOffset,
    const char *needle, int needleLen)
{
    uchar skiptable[256];
    bm_init_skiptable((const uchar *)needle, needleLen, skiptable);
    if (haystackOffset < 0)
        haystackOffset = 0;
    return bm_find((const uchar *)haystack, haystackLen, haystackOffset,
                   (const uchar *)needle, needleLen, skiptable);
}

#define REHASH(a) \
    if (sl_minus_1 < sizeof(uint) * CHAR_BIT) \
        hashHaystack -= (a) << sl_minus_1; \
    hashHaystack <<= 1

int qFindByteArray(
    const char *haystack0, int haystackLen, int from,
    const char *needle, int needleLen)
{
    const int l = haystackLen;
    const int sl = needleLen;
    if (from < 0)
        from += l;
    if (uint(sl + from) > (uint)l)
        return -1;
    if (!sl)
        return from;
    if (!l)
        return -1;

    if (sl == 1)
        return findChar(haystack0, haystackLen, needle[0], from);

    /*
      We use the Boyer-Moore algorithm in cases where the overhead
      for the skip table should pay off, otherwise we use a simple
      hash function.
    */
    if (l > 500 && sl > 5)
        return qFindByteArrayBoyerMoore(haystack0, haystackLen, from,
                                        needle, needleLen);

    /*
      We use some hashing for efficiency's sake. Instead of
      comparing strings, we compare the hash value of str with that
      of a part of this QString. Only if that matches, we call memcmp().
    */
    const char *haystack = haystack0 + from;
    const char *end = haystack0 + (l - sl);
    const uint sl_minus_1 = sl - 1;
    uint hashNeedle = 0, hashHaystack = 0;
    int idx;
    for (idx = 0; idx < sl; ++idx) {
        hashNeedle = ((hashNeedle<<1) + needle[idx]);
        hashHaystack = ((hashHaystack<<1) + haystack[idx]);
    }
    hashHaystack -= *(haystack + sl_minus_1);

    while (haystack <= end) {
        hashHaystack += *(haystack + sl_minus_1);
        if (hashHaystack == hashNeedle && *needle == *haystack
             && memcmp(needle, haystack, sl) == 0)
            return haystack - haystack0;

        REHASH(*haystack);
        ++haystack;
    }
    return -1;
}

QT_END_NAMESPACE