gecko/layout/style/nsCSSDataBlock.h

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is nsCSSDataBlock.h.
 *
 * The Initial Developer of the Original Code is L. David Baron.
 * Portions created by the Initial Developer are Copyright (C) 2003
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   L. David Baron <dbaron@dbaron.org> (original author)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

/*
 * compact representation of the property-value pairs within a CSS
 * declaration, and the code for expanding and compacting it
 */

#ifndef nsCSSDataBlock_h__
#define nsCSSDataBlock_h__

#include "nsCSSStruct.h"
#include "nsCSSProps.h"
#include "nsCSSPropertySet.h"

struct nsRuleData;
class nsCSSExpandedDataBlock;

namespace mozilla {
namespace css {
class Declaration;
}
}

/**
 * An |nsCSSCompressedDataBlock| holds a usually-immutable chunk of
 * property-value data for a CSS declaration block (which we misname a
 * |css::Declaration|).  Mutation is accomplished through
 * |nsCSSExpandedDataBlock| or in some cases via direct slot access.
 */
class nsCSSCompressedDataBlock {
private:
    friend class nsCSSExpandedDataBlock;

    // Only this class (via |CreateEmptyBlock|) or nsCSSExpandedDataBlock
    // (in |Compress|) can create compressed data blocks.
    nsCSSCompressedDataBlock() : mStyleBits(0) {}

public:
    ~nsCSSCompressedDataBlock();

    /**
     * Do what |nsIStyleRule::MapRuleInfoInto| needs to do for a style
     * rule using this block for storage.
     */
    void MapRuleInfoInto(nsRuleData *aRuleData) const;

    /**
     * Return the location at which the *value* for the property is
     * stored, or null if the block does not contain a value for the
     * property.  This is either an |nsCSSValue*|, |nsCSSRect*|, or an
     * |nsCSSValueList**|, etc.
     *
     * Inefficient (by design).
     *
     * Must not be called for shorthands.
     */
    const void* StorageFor(nsCSSProperty aProperty) const;

    /**
     * As above, but provides mutable access to a value slot.
     */
    void* SlotForValue(nsCSSProperty aProperty) {
      return const_cast<void*>(StorageFor(aProperty));
    }

    /**
     * A set of slightly more typesafe helpers for the above.  All
     * return null if the value is not present.
     */
    const nsCSSValue* ValueStorageFor(nsCSSProperty aProperty) const {
      NS_ABORT_IF_FALSE(nsCSSProps::kTypeTable[aProperty] == eCSSType_Value,
                        "type mismatch");
      return static_cast<const nsCSSValue*>(StorageFor(aProperty));
    }

    /**
     * Clone this block, or return null on out-of-memory.
     */
    nsCSSCompressedDataBlock* Clone() const;

    /**
     * Create a new nsCSSCompressedDataBlock holding no declarations.
     */
    static nsCSSCompressedDataBlock* CreateEmptyBlock();

    /**
     * Does a fast move of aSource to aDest.  The previous value in
     * aDest is cleanly destroyed, and aSource is cleared.  *aChanged
     * is set true if, before the copy, the value at aSource compares
     * unequal to the value at aDest.
     *
     * This can only be used for non-shorthand properties.  The caller
     * must make sure that the source and destination locations point
     * to the right kind of objects for the property id.
     */
    static void MoveValue(void *aSource, void *aDest, nsCSSProperty aPropID,
                          PRBool* aChanged);

private:
    PRInt32 mStyleBits; // the structs for which we have data, according to
                        // |nsCachedStyleData::GetBitForSID|.

    enum { block_chars = 4 }; // put 4 chars in the definition of the class
                              // to ensure size not inflated by alignment

    void* operator new(size_t aBaseSize, size_t aDataSize) {
        // subtract off the extra size to store |mBlock_|
        return ::operator new(aBaseSize + aDataSize -
                              sizeof(char) * block_chars);
    }

    /**
     * Delete all the data stored in this block, and the block itself.
     */
    void Destroy();

    char* mBlockEnd; // the byte after the last valid byte
    char mBlock_[block_chars]; // must be the last member!

    char* Block() { return mBlock_; }
    char* BlockEnd() { return mBlockEnd; }
    const char* Block() const { return mBlock_; }
    const char* BlockEnd() const { return mBlockEnd; }
    ptrdiff_t DataSize() const { return BlockEnd() - Block(); }
};

class nsCSSExpandedDataBlock {
public:
    nsCSSExpandedDataBlock();
    ~nsCSSExpandedDataBlock();
    /*
     * When setting properties in an |nsCSSExpandedDataBlock|, callers
     * must make the appropriate |AddPropertyBit| call.
     */

    nsCSSFont mFont;
    nsCSSDisplay mDisplay;
    nsCSSMargin mMargin;
    nsCSSList mList;
    nsCSSPosition mPosition;
    nsCSSTable mTable;
    nsCSSColor mColor;
    nsCSSContent mContent;
    nsCSSText mText;
    nsCSSUserInterface mUserInterface;
    nsCSSAural mAural;
    nsCSSPage mPage;
    nsCSSBreaks mBreaks;
    nsCSSXUL mXUL;
    nsCSSSVG mSVG;
    nsCSSColumn mColumn;

    /**
     * Transfer all of the state from a pair of compressed data blocks
     * to this expanded block.  This expanded block must be clear
     * beforehand.
     *
     * This method DELETES both of the compressed data blocks it is
     * passed.  (This is necessary because ownership of sub-objects
     * is transferred to the expanded block.)
     */
    void Expand(nsCSSCompressedDataBlock *aNormalBlock,
                nsCSSCompressedDataBlock *aImportantBlock);

    /**
     * Allocate a new compressed block and transfer all of the state
     * from this expanded block to the new compressed block, clearing
     * the state of this expanded block.
     */
    void Compress(nsCSSCompressedDataBlock **aNormalBlock,
                  nsCSSCompressedDataBlock **aImportantBlock);

    /**
     * Clear the state of this expanded block.
     */
    void Clear();

    /**
     * Clear the data for the given property (including the set and
     * important bits).  Can be used with shorthand properties.
     */
    void ClearProperty(nsCSSProperty aPropID);

    /**
     * Same as ClearProperty, but faster and cannot be used with shorthands.
     */
    void ClearLonghandProperty(nsCSSProperty aPropID);

    /**
     * Transfer the state for |aPropID| (which may be a shorthand)
     * from |aFromBlock| to this block.  The property being transferred
     * is !important if |aIsImportant| is true, and should replace an
     * existing !important property regardless of its own importance
     * if |aOverrideImportant| is true.
     *
     * Sets |*aChanged| to true if something changed, leaves it
     * unmodified otherwise.  Calls |ValueAppended| on |aDeclaration|
     * if the property was not previously set, or in any case if
     * |aMustCallValueAppended| is true.
     */
    void TransferFromBlock(nsCSSExpandedDataBlock& aFromBlock,
                           nsCSSProperty aPropID,
                           PRBool aIsImportant,
                           PRBool aOverrideImportant,
                           PRBool aMustCallValueAppended,
                           mozilla::css::Declaration* aDeclaration,
                           PRBool* aChanged);

    void AssertInitialState() {
#ifdef DEBUG
        DoAssertInitialState();
#endif
    }

private:
    /**
     * Compute the size that will be occupied by the result of
     * |Compress|.
     */
    struct ComputeSizeResult {
        PRUint32 normal, important;
    };
    ComputeSizeResult ComputeSize();

    void DoExpand(nsCSSCompressedDataBlock *aBlock, PRBool aImportant);

    /**
     * Worker for TransferFromBlock; cannot be used with shorthands.
     */
    void DoTransferFromBlock(nsCSSExpandedDataBlock& aFromBlock,
                             nsCSSProperty aPropID,
                             PRBool aIsImportant,
                             PRBool aOverrideImportant,
                             PRBool aMustCallValueAppended,
                             mozilla::css::Declaration* aDeclaration,
                             PRBool* aChanged);

#ifdef DEBUG
    void DoAssertInitialState();
#endif

    // XXX These could probably be pointer-to-member, if the casting can
    // be done correctly.
    static const size_t kOffsetTable[];

    /*
     * mPropertiesSet stores a bit for every property that is present,
     * to optimize compression of blocks with small numbers of
     * properties (the norm) and to allow quickly checking whether a
     * property is set in this block.
     */
    nsCSSPropertySet mPropertiesSet;
    /*
     * mPropertiesImportant indicates which properties are '!important'.
     */
    nsCSSPropertySet mPropertiesImportant;

public:
    /*
     * Return the storage location within |this| of the value of the
     * property (i.e., either an |nsCSSValue*|, |nsCSSRect*|, or
     * |nsCSSValueList**| (etc.).
     */
    void* PropertyAt(nsCSSProperty aProperty) {
        size_t offset = nsCSSExpandedDataBlock::kOffsetTable[aProperty];
        return reinterpret_cast<void*>(reinterpret_cast<char*>(this) + offset);
    }

    void SetPropertyBit(nsCSSProperty aProperty) {
        mPropertiesSet.AddProperty(aProperty);
    }

    void ClearPropertyBit(nsCSSProperty aProperty) {
        mPropertiesSet.RemoveProperty(aProperty);
    }

    PRBool HasPropertyBit(nsCSSProperty aProperty) {
        return mPropertiesSet.HasProperty(aProperty);
    }

    void SetImportantBit(nsCSSProperty aProperty) {
        mPropertiesImportant.AddProperty(aProperty);
    }

    void ClearImportantBit(nsCSSProperty aProperty) {
        mPropertiesImportant.RemoveProperty(aProperty);
    }

    PRBool HasImportantBit(nsCSSProperty aProperty) {
        return mPropertiesImportant.HasProperty(aProperty);
    }

    void ClearSets() {
        mPropertiesSet.Empty();
        mPropertiesImportant.Empty();
    }
};

#endif /* !defined(nsCSSDataBlock_h__) */