BreakLines.h   [plain text]

/*
 * Copyright (C) 2005, 2007, 2010, 2013, 2016 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.
 *
 */

#pragma once

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

namespace WebCore {

static const UChar lineBreakTableFirstCharacter = '!';
static const UChar lineBreakTableLastCharacter = 127;
static const unsigned lineBreakTableColumnCount = (lineBreakTableLastCharacter - lineBreakTableFirstCharacter) / 8 + 1;

WEBCORE_EXPORT extern const unsigned char lineBreakTable[][lineBreakTableColumnCount];

enum class NonBreakingSpaceBehavior {
    IgnoreNonBreakingSpace,
    TreatNonBreakingSpaceAsBreak,
};

enum class CanUseShortcut {
    Yes,
    No
};

template<NonBreakingSpaceBehavior nonBreakingSpaceBehavior>
static inline bool isBreakableSpace(UChar character)
{
    switch (character) {
    case ' ':
    case '\n':
    case '\t':
        return true;
    case noBreakSpace:
        return nonBreakingSpaceBehavior == NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak;
    default:
        return false;
    }
}

inline bool shouldBreakAfter(UChar lastCharacter, UChar character, UChar nextCharacter)
{
    // 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 (character == '-' && isASCIIDigit(nextCharacter))
        return isASCIIAlphanumeric(lastCharacter);

    // 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 (character >= lineBreakTableFirstCharacter && character <= lineBreakTableLastCharacter && nextCharacter >= lineBreakTableFirstCharacter && nextCharacter <= lineBreakTableLastCharacter) {
        const unsigned char* tableRow = lineBreakTable[character - lineBreakTableFirstCharacter];
        unsigned nextCharacterIndex = nextCharacter - lineBreakTableFirstCharacter;
        return tableRow[nextCharacterIndex / 8] & (1 << (nextCharacterIndex % 8));
    }
    // Otherwise defer to the Unicode algorithm by returning false.
    return false;
}

template<NonBreakingSpaceBehavior nonBreakingSpaceBehavior>
inline bool needsLineBreakIterator(UChar character)
{
    if (nonBreakingSpaceBehavior == NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak)
        return character > lineBreakTableLastCharacter;
    return character > lineBreakTableLastCharacter && character != noBreakSpace;
}

// When in non-loose mode, we can use the ASCII shortcut table.
template<typename CharacterType, NonBreakingSpaceBehavior nonBreakingSpaceBehavior, CanUseShortcut canUseShortcut>
inline unsigned nextBreakablePosition(LazyLineBreakIterator& lazyBreakIterator, const CharacterType* string, unsigned length, unsigned startPosition)
{
    std::optional<unsigned> nextBreak;

    CharacterType lastLastCharacter = startPosition > 1 ? string[startPosition - 2] : static_cast<CharacterType>(lazyBreakIterator.secondToLastCharacter());
    CharacterType lastCharacter = startPosition > 0 ? string[startPosition - 1] : static_cast<CharacterType>(lazyBreakIterator.lastCharacter());
    unsigned priorContextLength = lazyBreakIterator.priorContextLength();
    for (unsigned i = startPosition; i < length; i++) {
        CharacterType character = string[i];

        if (isBreakableSpace<nonBreakingSpaceBehavior>(character) || (canUseShortcut == CanUseShortcut::Yes && shouldBreakAfter(lastLastCharacter, lastCharacter, character)))
            return i;

        if (canUseShortcut == CanUseShortcut::No || needsLineBreakIterator<nonBreakingSpaceBehavior>(character) || needsLineBreakIterator<nonBreakingSpaceBehavior>(lastCharacter)) {
            if (!nextBreak || nextBreak.value() < i) {
                // Don't break if positioned at start of primary context and there is no prior context.
                if (i || priorContextLength) {
                    UBreakIterator* breakIterator = lazyBreakIterator.get(priorContextLength);
                    if (breakIterator) {
                        int candidate = ubrk_following(breakIterator, i - 1 + priorContextLength);
                        if (candidate == UBRK_DONE)
                            nextBreak = std::nullopt;
                        else {
                            unsigned result = candidate;
                            ASSERT(result >= priorContextLength);
                            nextBreak = result - priorContextLength;
                        }
                    }
                }
            }
            if (i == nextBreak && !isBreakableSpace<nonBreakingSpaceBehavior>(lastCharacter))
                return i;
        }

        lastLastCharacter = lastCharacter;
        lastCharacter = character;
    }

    return length;
}

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

inline unsigned nextBreakablePositionKeepingAllWords(LazyLineBreakIterator& lazyBreakIterator, unsigned startPosition)
{
    auto stringView = lazyBreakIterator.stringView();
    if (stringView.is8Bit())
        return nextBreakablePositionKeepingAllWords<LChar, NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak>(stringView.characters8(), stringView.length(), startPosition);
    return nextBreakablePositionKeepingAllWords<UChar, NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak>(stringView.characters16(), stringView.length(), startPosition);
}

inline unsigned nextBreakablePositionKeepingAllWordsIgnoringNBSP(LazyLineBreakIterator& iterator, unsigned startPosition)
{
    auto stringView = iterator.stringView();
    if (stringView.is8Bit())
        return nextBreakablePositionKeepingAllWords<LChar, NonBreakingSpaceBehavior::IgnoreNonBreakingSpace>(stringView.characters8(), stringView.length(), startPosition);
    return nextBreakablePositionKeepingAllWords<UChar, NonBreakingSpaceBehavior::IgnoreNonBreakingSpace>(stringView.characters16(), stringView.length(), startPosition);
}

inline unsigned nextBreakablePosition(LazyLineBreakIterator& iterator, unsigned startPosition)
{
    auto stringView = iterator.stringView();
    if (stringView.is8Bit())
        return nextBreakablePosition<LChar, NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak, CanUseShortcut::Yes>(iterator, stringView.characters8(), stringView.length(), startPosition);
    return nextBreakablePosition<UChar, NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak, CanUseShortcut::Yes>(iterator, stringView.characters16(), stringView.length(), startPosition);
}

inline unsigned nextBreakablePositionIgnoringNBSP(LazyLineBreakIterator& lazyBreakIterator, unsigned startPosition)
{
    auto stringView = lazyBreakIterator.stringView();
    if (stringView.is8Bit())
        return nextBreakablePosition<LChar, NonBreakingSpaceBehavior::IgnoreNonBreakingSpace, CanUseShortcut::Yes>(lazyBreakIterator, stringView.characters8(), stringView.length(), startPosition);
    return nextBreakablePosition<UChar, NonBreakingSpaceBehavior::IgnoreNonBreakingSpace, CanUseShortcut::Yes>(lazyBreakIterator, stringView.characters16(), stringView.length(), startPosition);
}

inline unsigned nextBreakablePositionWithoutShortcut(LazyLineBreakIterator& lazyBreakIterator, unsigned startPosition)
{
    auto stringView = lazyBreakIterator.stringView();
    if (stringView.is8Bit())
        return nextBreakablePosition<LChar, NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak, CanUseShortcut::No>(lazyBreakIterator, stringView.characters8(), stringView.length(), startPosition);
    return nextBreakablePosition<UChar, NonBreakingSpaceBehavior::TreatNonBreakingSpaceAsBreak, CanUseShortcut::No>(lazyBreakIterator, stringView.characters16(), stringView.length(), startPosition);
}

inline unsigned nextBreakablePositionIgnoringNBSPWithoutShortcut(LazyLineBreakIterator& lazyBreakIterator, unsigned startPosition)
{
    auto stringView = lazyBreakIterator.stringView();
    if (stringView.is8Bit())
        return nextBreakablePosition<LChar, NonBreakingSpaceBehavior::IgnoreNonBreakingSpace, CanUseShortcut::No>(lazyBreakIterator, stringView.characters8(), stringView.length(), startPosition);
    return nextBreakablePosition<UChar, NonBreakingSpaceBehavior::IgnoreNonBreakingSpace, CanUseShortcut::No>(lazyBreakIterator, stringView.characters16(), stringView.length(), startPosition);
}

inline bool isBreakable(LazyLineBreakIterator& lazyBreakIterator, unsigned startPosition, std::optional<unsigned>& nextBreakable, bool breakNBSP, bool canUseShortcut, bool keepAllWords)
{
    if (nextBreakable && nextBreakable.value() >= startPosition)
        return startPosition == nextBreakable;

    if (keepAllWords) {
        if (breakNBSP)
            nextBreakable = nextBreakablePositionKeepingAllWords(lazyBreakIterator, startPosition);
        else
            nextBreakable = nextBreakablePositionKeepingAllWordsIgnoringNBSP(lazyBreakIterator, startPosition);
    } else if (!canUseShortcut) {
        if (breakNBSP)
            nextBreakable = nextBreakablePositionWithoutShortcut(lazyBreakIterator, startPosition);
        else
            nextBreakable = nextBreakablePositionIgnoringNBSPWithoutShortcut(lazyBreakIterator, startPosition);
    } else {
        if (breakNBSP)
            nextBreakable = nextBreakablePosition(lazyBreakIterator, startPosition);
        else
            nextBreakable = nextBreakablePositionIgnoringNBSP(lazyBreakIterator, startPosition);
    }
    return startPosition == nextBreakable;
}

} // namespace WebCore