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1 
2 /*
3  * Copyright 2010 Google Inc.
4  *
5  * Use of this source code is governed by a BSD-style license that can be
6  * found in the LICENSE file.
7  */
8 
9 
10 #ifndef GrTemplates_DEFINED
11 #define GrTemplates_DEFINED
12 
13 #include "GrNoncopyable.h"
14 
15 /**
16  *  Use to cast a ptr to a different type, and maintain strict-aliasing
17  */
GrTCast(Src src)18 template <typename Dst, typename Src> Dst GrTCast(Src src) {
19     union {
20         Src src;
21         Dst dst;
22     } data;
23     data.src = src;
24     return data.dst;
25 }
26 
27 /**
28  * takes a T*, saves the value it points to,  in and restores the value in the
29  * destructor
30  * e.g.:
31  * {
32  *      GrAutoTRestore<int*> autoCountRestore;
33  *      if (useExtra) {
34  *          autoCountRestore.reset(&fCount);
35  *          fCount += fExtraCount;
36  *      }
37  *      ...
38  * }  // fCount is restored
39  */
40 template <typename T> class GrAutoTRestore : public GrNoncopyable {
41 public:
GrAutoTRestore()42     GrAutoTRestore() : fPtr(NULL), fVal() {}
43 
GrAutoTRestore(T * ptr)44     GrAutoTRestore(T* ptr) {
45         fPtr = ptr;
46         if (NULL != ptr) {
47             fVal = *ptr;
48         }
49     }
50 
~GrAutoTRestore()51     ~GrAutoTRestore() {
52         if (NULL != fPtr) {
53             *fPtr = fVal;
54         }
55     }
56 
57     // restores previously saved value (if any) and saves value for passed T*
reset(T * ptr)58     void reset(T* ptr) {
59         if (NULL != fPtr) {
60             *fPtr = fVal;
61         }
62         fPtr = ptr;
63         fVal = *ptr;
64     }
65 private:
66     T* fPtr;
67     T  fVal;
68 };
69 
70 #endif
71