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

struct nsRuleData;
class nsCSSExpandedDataBlock;

namespace mozilla {
namespace css {
class Declaration;
}
}

/*
 * nsCSSCompressedDataBlock holds property-value pairs corresponding
 * to CSS declaration blocks.  Each pair is stored in a CDBValueStorage
 * object; these objects form an array at the end of the data block.
 */
struct CDBValueStorage {
    nsCSSProperty property;
    nsCSSValue value;
};

/**
 * 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.
     *
     * Inefficient (by design).
     *
     * Must not be called for shorthands.
     */
    const nsCSSValue* ValueFor(nsCSSProperty aProperty) const;

    /**
     * Attempt to replace the value for |aProperty| stored in this block
     * with the matching value stored in |aFromBlock|.
     * This method will fail (returning false) if |aProperty| is not
     * already in this block.  It will set |aChanged| to true if it
     * actually made a change to the block, but regardless, if it
     * returns true, the value in |aFromBlock| was erased.
     */
    bool TryReplaceValue(nsCSSProperty aProperty,
                           nsCSSExpandedDataBlock& aFromBlock,
                           bool* aChanged);

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

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

    size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const;

private:
    void* operator new(size_t aBaseSize, size_t aDataSize) {
        NS_ABORT_IF_FALSE(aBaseSize == sizeof(nsCSSCompressedDataBlock),
                          "unexpected size for nsCSSCompressedDataBlock");
        return ::operator new(aBaseSize + aDataSize);
    }

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

    PRInt32 mStyleBits; // the structs for which we have data, according to
                        // |nsCachedStyleData::GetBitForSID|.
    PRUint32 mDataSize;
    // CDBValueStorage elements are stored after these fields.  Space for them
    // is allocated in |operator new| above.  The static assertions following
    // this class make sure that the CDBValueStorage elements are aligned
    // appropriately.
    
    char* Block() { return (char*)this + sizeof(*this); }
    char* BlockEnd() { return Block() + mDataSize; }
    const char* Block() const { return (char*)this + sizeof(*this); }
    const char* BlockEnd() const { return Block() + mDataSize; }
    void SetBlockEnd(char *blockEnd) { 
        /*
         * Note:  if we ever change nsCSSDeclaration to store the declarations
         * in order and also store repeated declarations of the same property,
         * then we need to worry about checking for integer overflow here.
         */
        NS_ABORT_IF_FALSE(size_t(blockEnd - Block()) <= size_t(PR_UINT32_MAX),
                          "overflow of mDataSize");
        mDataSize = PRUint32(blockEnd - Block());
    }
    ptrdiff_t DataSize() const { return mDataSize; }
};

/* Make sure the CDBValueStorage elements are aligned appropriately. */
PR_STATIC_ASSERT(sizeof(nsCSSCompressedDataBlock) == 8);
PR_STATIC_ASSERT(NS_ALIGNMENT_OF(CDBValueStorage) <= 8); 

class nsCSSExpandedDataBlock {
    friend class nsCSSCompressedDataBlock;

public:
    nsCSSExpandedDataBlock();
    ~nsCSSExpandedDataBlock();

private:
    /* Property storage may not be accessed directly; use AddLonghandProperty
     * and friends.
     */
    nsCSSValue mValues[eCSSProperty_COUNT_no_shorthands];

public:
    /**
     * 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 new compressed blocks and transfer all of the state
     * from this expanded block to the new blocks, clearing this
     * expanded block.  A normal block will always be allocated, but
     * an important block will only be allocated if there are
     * !important properties in the expanded block; otherwise
     * |*aImportantBlock| will be set to null.
     */
    void Compress(nsCSSCompressedDataBlock **aNormalBlock,
                  nsCSSCompressedDataBlock **aImportantBlock);

    /**
     * Copy a value into this expanded block.  This does NOT destroy
     * the source value object.  |aProperty| cannot be a shorthand.
     */
    void AddLonghandProperty(nsCSSProperty aProperty, const nsCSSValue& aValue);

    /**
     * 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.
     *
     * Returns true if something changed, false otherwise.  Calls
     * |ValueAppended| on |aDeclaration| if the property was not
     * previously set, or in any case if |aMustCallValueAppended| is true.
     */
    bool TransferFromBlock(nsCSSExpandedDataBlock& aFromBlock,
                             nsCSSProperty aPropID,
                             bool aIsImportant,
                             bool aOverrideImportant,
                             bool aMustCallValueAppended,
                             mozilla::css::Declaration* aDeclaration);

    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, bool aImportant);

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

#ifdef DEBUG
    void DoAssertInitialState();
#endif

    /*
     * 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;

    /*
     * Return the storage location within |this| of the value of the
     * property |aProperty|.
     */
    nsCSSValue* PropertyAt(nsCSSProperty aProperty) {
        NS_ABORT_IF_FALSE(0 <= aProperty &&
                          aProperty < eCSSProperty_COUNT_no_shorthands,
                          "property out of range");
        return &mValues[aProperty];
    }

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

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

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

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

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

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

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

#endif /* !defined(nsCSSDataBlock_h__) */