break_lines.h   [plain text]

/*
 * Copyright (C) 2005, 2007, 2010, 2013 Apple Inc. All rights reserved.
 * Copyright (C) 2011 Google Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef break_lines_h
#define break_lines_h

#include <wtf/ASCIICType.h>
#include <wtf/StdLibExtras.h>
#include <wtf/text/TextBreakIterator.h>
#include <wtf/unicode/CharacterNames.h>

namespace WebCore {

static const UChar asciiLineBreakTableFirstChar = '!';
static const UChar asciiLineBreakTableLastChar = 127;
static const unsigned asciiLineBreakTableColumnCount = (asciiLineBreakTableLastChar - asciiLineBreakTableFirstChar) / 8 + 1;

WEBCORE_EXPORT extern const unsigned char asciiLineBreakTable[][asciiLineBreakTableColumnCount];

enum class NBSPBehavior {
    IgnoreNBSP,
    TreatNBSPAsBreak,
};

template<NBSPBehavior nbspBehavior>
static inline bool isBreakableSpace(UChar ch)
{
    switch (ch) {
    case ' ':
    case '\n':
    case '\t':
        return true;
    case noBreakSpace:
        return nbspBehavior == NBSPBehavior::TreatNBSPAsBreak;
    default:
        return false;
    }
}

inline bool shouldBreakAfter(UChar lastCh, UChar ch, UChar nextCh)
{
    // Don't allow line breaking between '-' and a digit if the '-' may mean a minus sign in the context,
    // while allow breaking in 'ABCD-1234' and '1234-5678' which may be in long URLs.
    if (ch == '-' && isASCIIDigit(nextCh))
        return isASCIIAlphanumeric(lastCh);

    // If both ch and nextCh are ASCII characters, use a lookup table for enhanced speed and for compatibility
    // with other browsers (see comments for asciiLineBreakTable for details).
    if (ch >= asciiLineBreakTableFirstChar && ch <= asciiLineBreakTableLastChar && nextCh >= asciiLineBreakTableFirstChar && nextCh <= asciiLineBreakTableLastChar) {
        const unsigned char* tableRow = asciiLineBreakTable[ch - asciiLineBreakTableFirstChar];
        int nextChIndex = nextCh - asciiLineBreakTableFirstChar;
        return tableRow[nextChIndex / 8] & (1 << (nextChIndex % 8));
    }
    // Otherwise defer to the Unicode algorithm by returning false.
    return false;
}

template<NBSPBehavior nbspBehavior>
inline bool needsLineBreakIterator(UChar ch)
{
    if (nbspBehavior == NBSPBehavior::TreatNBSPAsBreak)
        return ch > asciiLineBreakTableLastChar;
    return ch > asciiLineBreakTableLastChar && ch != noBreakSpace;
}

// When in non-loose mode, we can use the ASCII shortcut table.
template<typename CharacterType, NBSPBehavior nbspBehavior>
inline int nextBreakablePositionNonLoosely(LazyLineBreakIterator& lazyBreakIterator, const CharacterType* str, unsigned length, int pos)
{
    int len = static_cast<int>(length);
    int nextBreak = -1;

    CharacterType lastLastCh = pos > 1 ? str[pos - 2] : static_cast<CharacterType>(lazyBreakIterator.secondToLastCharacter());
    CharacterType lastCh = pos > 0 ? str[pos - 1] : static_cast<CharacterType>(lazyBreakIterator.lastCharacter());
    unsigned priorContextLength = lazyBreakIterator.priorContextLength();
    for (int i = pos; i < len; i++) {
        CharacterType ch = str[i];

        // Non-loose mode, so use ASCII shortcut (shouldBreakAfter) if not breakable space.
        if (isBreakableSpace<nbspBehavior>(ch) || shouldBreakAfter(lastLastCh, lastCh, ch))
            return i;

        // Non-loose mode, so conditionally use break iterator.
        if (needsLineBreakIterator<nbspBehavior>(ch) || needsLineBreakIterator<nbspBehavior>(lastCh)) {
            if (nextBreak < i) {
                // Don't break if positioned at start of primary context and there is no prior context.
                if (i || priorContextLength) {
                    TextBreakIterator* breakIterator = lazyBreakIterator.get(priorContextLength);
                    if (breakIterator) {
                        nextBreak = textBreakFollowing(breakIterator, i - 1 + priorContextLength);
                        if (nextBreak >= 0)
                            nextBreak -= priorContextLength;
                    }
                }
            }
            if (i == nextBreak && !isBreakableSpace<nbspBehavior>(lastCh))
                return i;
        }

        lastLastCh = lastCh;
        lastCh = ch;
    }

    return len;
}

// When in loose mode, we can't use the ASCII shortcut table since loose mode allows "$100" to break after '$' in content marked as CJK.
// N.B. It should be possible to combine the following with the non-loose version above by adding a LooseBehavior template parameter;
// however, when doing this, a 10% performance regression appeared on chromium-win (https://bugs.webkit.org/show_bug.cgi?id=89235#c112).
template<typename CharacterType, NBSPBehavior nbspBehavior>
static inline int nextBreakablePositionLoosely(LazyLineBreakIterator& lazyBreakIterator, const CharacterType* str, unsigned length, int pos)
{
    int len = static_cast<int>(length);
    int nextBreak = -1;

    CharacterType lastCh = pos > 0 ? str[pos - 1] : static_cast<CharacterType>(lazyBreakIterator.lastCharacter());
    unsigned priorContextLength = lazyBreakIterator.priorContextLength();
    for (int i = pos; i < len; i++) {
        CharacterType ch = str[i];

        // Always loose mode, so don't use ASCII shortcut (shouldBreakAfter).
        if (isBreakableSpace<nbspBehavior>(ch))
            return i;

        // Always use line break iterator in loose mode.
        if (nextBreak < i) {
            // Don't break if positioned at start of primary context and there is no prior context.
            if (i || priorContextLength) {
                TextBreakIterator* breakIterator = lazyBreakIterator.get(priorContextLength);
                if (breakIterator) {
                    nextBreak = textBreakFollowing(breakIterator, i - 1 + priorContextLength);
                    if (nextBreak >= 0)
                        nextBreak -= priorContextLength;
                }
            }
        }
        if (i == nextBreak && !isBreakableSpace<nbspBehavior>(lastCh))
            return i;

        lastCh = ch;
    }

    return len;
}

template<typename CharacterType, NBSPBehavior nbspBehavior>
inline unsigned nextBreakablePositionKeepingAllWords(const CharacterType* string, unsigned length, unsigned startPosition)
{
    for (unsigned i = startPosition; i < length; i++) {
        if (isBreakableSpace<nbspBehavior>(string[i]))
            return i;
    }
    return length;
}

inline unsigned nextBreakablePositionKeepingAllWords(LazyLineBreakIterator& lazyBreakIterator, int startPosition)
{
    String string = lazyBreakIterator.string();
    if (string.is8Bit())
        return nextBreakablePositionKeepingAllWords<LChar, NBSPBehavior::TreatNBSPAsBreak>(string.characters8(), string.length(), startPosition);
    return nextBreakablePositionKeepingAllWords<UChar, NBSPBehavior::TreatNBSPAsBreak>(string.characters16(), string.length(), startPosition);
}

inline unsigned nextBreakablePositionKeepingAllWordsIgnoringNBSP(LazyLineBreakIterator& iterator, int startPosition)
{
    String string = iterator.string();
    if (string.is8Bit())
        return nextBreakablePositionKeepingAllWords<LChar, NBSPBehavior::IgnoreNBSP>(string.characters8(), string.length(), startPosition);
    return nextBreakablePositionKeepingAllWords<UChar, NBSPBehavior::IgnoreNBSP>(string.characters16(), string.length(), startPosition);
}

inline int nextBreakablePosition(LazyLineBreakIterator& iterator, int pos)
{
    String string = iterator.string();
    if (string.is8Bit())
        return nextBreakablePositionNonLoosely<LChar, NBSPBehavior::TreatNBSPAsBreak>(iterator, string.characters8(), string.length(), pos);
    return nextBreakablePositionNonLoosely<UChar, NBSPBehavior::TreatNBSPAsBreak>(iterator, string.characters16(), string.length(), pos);
}

inline int nextBreakablePositionIgnoringNBSP(LazyLineBreakIterator& lazyBreakIterator, int pos)
{
    String string = lazyBreakIterator.string();
    if (string.is8Bit())
        return nextBreakablePositionNonLoosely<LChar, NBSPBehavior::IgnoreNBSP>(lazyBreakIterator, string.characters8(), string.length(), pos);
    return nextBreakablePositionNonLoosely<UChar, NBSPBehavior::IgnoreNBSP>(lazyBreakIterator, string.characters16(), string.length(), pos);
}

inline int nextBreakablePositionLoose(LazyLineBreakIterator& lazyBreakIterator, int pos)
{
    String string = lazyBreakIterator.string();
    if (string.is8Bit())
        return nextBreakablePositionLoosely<LChar, NBSPBehavior::TreatNBSPAsBreak>(lazyBreakIterator, string.characters8(), string.length(), pos);
    return nextBreakablePositionLoosely<UChar, NBSPBehavior::TreatNBSPAsBreak>(lazyBreakIterator, string.characters16(), string.length(), pos);
}

inline int nextBreakablePositionIgnoringNBSPLoose(LazyLineBreakIterator& lazyBreakIterator, int pos)
{
    String string = lazyBreakIterator.string();
    if (string.is8Bit())
        return nextBreakablePositionLoosely<LChar, NBSPBehavior::IgnoreNBSP>(lazyBreakIterator, string.characters8(), string.length(), pos);
    return nextBreakablePositionLoosely<UChar, NBSPBehavior::IgnoreNBSP>(lazyBreakIterator, string.characters16(), string.length(), pos);
}

inline bool isBreakable(LazyLineBreakIterator& lazyBreakIterator, int pos, int& nextBreakable, bool breakNBSP, bool isLooseMode, bool keepAllWords)
{
    if (pos <= nextBreakable)
        return pos == nextBreakable;

    if (keepAllWords) {
        if (breakNBSP)
            nextBreakable = static_cast<int>(nextBreakablePositionKeepingAllWords(lazyBreakIterator, pos));
        else
            nextBreakable = static_cast<int>(nextBreakablePositionKeepingAllWordsIgnoringNBSP(lazyBreakIterator, pos));
    } else if (isLooseMode) {
        if (breakNBSP)
            nextBreakable = nextBreakablePositionLoose(lazyBreakIterator, pos);
        else
            nextBreakable = nextBreakablePositionIgnoringNBSPLoose(lazyBreakIterator, pos);
    } else {
        if (breakNBSP)
            nextBreakable = nextBreakablePosition(lazyBreakIterator, pos);
        else
            nextBreakable = nextBreakablePositionIgnoringNBSP(lazyBreakIterator, pos);
    }
    return pos == nextBreakable;
}

} // namespace WebCore

#endif // break_lines_h