gpu/include/GrTemplates.h

/*
    Copyright 2010 Google Inc.

    Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
 */

#ifndef GrTemplates_DEFINED
#define GrTemplates_DEFINED

#include "GrNoncopyable.h"

/**
 *  Use to cast a ptr to a different type, and maintain strict-aliasing
 */
template <typename Dst, typename Src> Dst GrTCast(Src src) {
    union {
        Src src;
        Dst dst;
    } data;
    data.src = src;
    return data.dst;
}

/**
 * Reserves memory that is aligned on double and pointer boundaries.
 * Hopefully this is sufficient for all practical purposes.
 */
template <size_t N> class GrAlignedSStorage : GrNoncopyable {
public:
    void* get() { return fData; }
private:
    union {
        void*   fPtr;
        double  fDouble;
        char    fData[N];
    };
};

/**
 * Reserves memory that is aligned on double and pointer boundaries.
 * Hopefully this is sufficient for all practical purposes. Otherwise,
 * we have to do some arcane trickery to determine alignment of non-POD
 * types. Lifetime of the memory is the lifetime of the object.
 */
template <int N, typename T> class GrAlignedSTStorage : GrNoncopyable {
public:
    /**
     * Returns void* because this object does not initialize the
     * memory. Use placement new for types that require a cons.
     */
    void* get() { return fStorage.get(); }
private:
    GrAlignedSStorage<sizeof(T)*N> fStorage;
};

/**
 * saves value of T* in and restores in destructor
 * e.g.:
 * {
 *      GrAutoTPtrValueRestore<int*> autoCountRestore;
 *      if (useExtra) {
 *          autoCountRestore.save(&fCount);
 *          fCount += fExtraCount;
 *      }
 *      ...
 * }  // fCount is restored
 */
template <typename T> class GrAutoTPtrValueRestore : public GrNoncopyable {
public:
    GrAutoTPtrValueRestore() : fPtr(NULL), fVal() {}
    
    GrAutoTPtrValueRestore(T* ptr) {
        fPtr = ptr;
        if (NULL != ptr) {
            fVal = *ptr;
        }
    }
    
    ~GrAutoTPtrValueRestore() {
        if (NULL != fPtr) {
            *fPtr = fVal;
        }
    }
    
    // restores previously saved value (if any) and saves value for passed T*
    void save(T* ptr) {
        if (NULL != fPtr) {
            *fPtr = fVal;
        }
        fPtr = ptr;
        fVal = *ptr;
    }
private:
    T* fPtr;
    T  fVal;
};

#endif