LCOV - app.info - objdir/dist/include/mozilla/Util.h

LCOV - code coverage report
| Current view: | directory - objdir/dist/include/mozilla - Util.h (source / functions) |  | Found | Hit | Coverage |
| Test: | app.info | Lines: | 58 | 58 | 100.0 %
| Date: | 2012-04-07 | Functions: | 158 | 149 | 94.3 %

           1                 : /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
           2                 :  * vim: set ts=8 sw=4 et tw=99 ft=cpp:
           3                 :  *
           4                 :  * ***** BEGIN LICENSE BLOCK *****
           5                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
           6                 :  *
           7                 :  * The contents of this file are subject to the Mozilla Public License Version
           8                 :  * 1.1 (the "License"); you may not use this file except in compliance with
           9                 :  * the License. You may obtain a copy of the License at:
          10                 :  * http://www.mozilla.org/MPL/
          11                 :  *
          12                 :  * Software distributed under the License is distributed on an "AS IS" basis,
          13                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
          14                 :  * for the specific language governing rights and limitations under the
          15                 :  * License.
          16                 :  *
          17                 :  * The Original Code is Mozilla Code.
          18                 :  *
          19                 :  * The Initial Developer of the Original Code is
          20                 :  *   The Mozilla Foundation
          21                 :  * Portions created by the Initial Developer are Copyright (C) 2011
          22                 :  * the Initial Developer. All Rights Reserved.
          23                 :  *
          24                 :  * Contributor(s):
          25                 :  *
          26                 :  * Alternatively, the contents of this file may be used under the terms of
          27                 :  * either the GNU General Public License Version 2 or later (the "GPL"), or
          28                 :  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
          29                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
          30                 :  * of those above. If you wish to allow use of your version of this file only
          31                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
          32                 :  * use your version of this file under the terms of the MPL, indicate your
          33                 :  * decision by deleting the provisions above and replace them with the notice
          34                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
          35                 :  * the provisions above, a recipient may use your version of this file under
          36                 :  * the terms of any one of the MPL, the GPL or the LGPL.
          37                 :  *
          38                 :  * ***** END LICENSE BLOCK ***** */
          39                 :
          40                 : /*
          41                 :  * Miscellaneous uncategorized functionality.  Please add new functionality to
          42                 :  * new headers, or to other appropriate existing headers, not here.
          43                 :  */
          44                 :
          45                 : #ifndef mozilla_Util_h_
          46                 : #define mozilla_Util_h_
          47                 :
          48                 : #include "mozilla/Assertions.h"
          49                 : #include "mozilla/Attributes.h"
          50                 : #include "mozilla/Types.h"
          51                 :
          52                 : #ifdef __cplusplus
          53                 :
          54                 : namespace mozilla {
          55                 :
          56                 : /**
          57                 :  * DebugOnly contains a value of type T, but only in debug builds.  In
          58                 :  * release builds, it does not contain a value.  This helper is
          59                 :  * intended to be used along with ASSERT()-style macros, allowing one
          60                 :  * to write
          61                 :  *
          62                 :  *   DebugOnly<bool> check = Func();
          63                 :  *   ASSERT(check);
          64                 :  *
          65                 :  * more concisely than declaring |check| conditional on #ifdef DEBUG,
          66                 :  * but also without allocating storage space for |check| in release
          67                 :  * builds.
          68                 :  *
          69                 :  * DebugOnly instances can only be coerced to T in debug builds; in
          70                 :  * release builds, they don't have a value so type coercion is not
          71                 :  * well defined.
          72                 :  */
          73                 : template <typename T>
          74                 : struct DebugOnly
          75                 : {
          76                 : #ifdef DEBUG
          77                 :     T value;
          78                 :
          79       185369610 :     DebugOnly() {}
          80       326461306 :     DebugOnly(const T& other) : value(other) {}
          81          666819 :     DebugOnly(const DebugOnly& other) : value(other.value) {}
          82          188163 :     DebugOnly& operator=(const T& rhs) {
          83          188163 :         value = rhs;
          84          188163 :         return *this;
          85                 :     }
          86       367655831 :     void operator++(int) {
          87       367655831 :         value++;
          88       367655831 :     }
          89           50996 :     void operator--(int) {
          90           50996 :         value--;
          91           50996 :     }
          92                 :
          93       854014893 :     operator T&() { return value; }
          94                 :     operator const T&() const { return value; }
          95                 :
          96       289688783 :     T& operator->() { return value; }
          97                 :
          98                 : #else
          99                 :     DebugOnly() {}
         100                 :     DebugOnly(const T&) {}
         101                 :     DebugOnly(const DebugOnly&) {}
         102                 :     DebugOnly& operator=(const T&) { return *this; }
         103                 :     void operator++(int) {}
         104                 :     void operator--(int) {}
         105                 : #endif
         106                 :
         107                 :     /*
         108                 :      * DebugOnly must always have a destructor or else it will
         109                 :      * generate "unused variable" warnings, exactly what it's intended
         110                 :      * to avoid!
         111                 :      */
         112       512497704 :     ~DebugOnly() {}
         113                 : };
         114                 :
         115                 : /*
         116                 :  * This class, and the corresponding macro MOZ_ALIGNOF, figure out how many
         117                 :  * bytes of alignment a given type needs.
         118                 :  */
         119                 : template<class T>
         120                 : struct AlignmentFinder
         121                 : {
         122                 : private:
         123                 :   struct Aligner
         124                 :   {
         125                 :     char c;
         126                 :     T t;
         127                 :   };
         128                 :
         129                 : public:
         130                 :   static const int alignment = sizeof(Aligner) - sizeof(T);
         131                 : };
         132                 :
         133                 : #define MOZ_ALIGNOF(T) mozilla::AlignmentFinder<T>::alignment
         134                 :
         135                 : /*
         136                 :  * Declare the MOZ_ALIGNED_DECL macro for declaring aligned types.
         137                 :  *
         138                 :  * For instance,
         139                 :  *
         140                 :  *   MOZ_ALIGNED_DECL(char arr[2], 8);
         141                 :  *
         142                 :  * will declare a two-character array |arr| aligned to 8 bytes.
         143                 :  */
         144                 :
         145                 : #if defined(__GNUC__)
         146                 : #  define MOZ_ALIGNED_DECL(_type, _align) \
         147                 :      _type __attribute__((aligned(_align)))
         148                 : #elif defined(_MSC_VER)
         149                 : #  define MOZ_ALIGNED_DECL(_type, _align) \
         150                 :      __declspec(align(_align)) _type
         151                 : #else
         152                 : #  warning "We don't know how to align variables on this compiler."
         153                 : #  define MOZ_ALIGNED_DECL(_type, _align) _type
         154                 : #endif
         155                 :
         156                 : /*
         157                 :  * AlignedElem<N> is a structure whose alignment is guaranteed to be at least N bytes.
         158                 :  *
         159                 :  * We support 1, 2, 4, 8, and 16-bit alignment.
         160                 :  */
         161                 : template<size_t align>
         162                 : struct AlignedElem;
         163                 :
         164                 : /*
         165                 :  * We have to specialize this template because GCC doesn't like __attribute__((aligned(foo))) where
         166                 :  * foo is a template parameter.
         167                 :  */
         168                 :
         169                 : template<>
         170                 : struct AlignedElem<1>
         171                 : {
         172                 :   MOZ_ALIGNED_DECL(uint8_t elem, 1);
         173                 : };
         174                 :
         175                 : template<>
         176                 : struct AlignedElem<2>
         177                 : {
         178                 :   MOZ_ALIGNED_DECL(uint8_t elem, 2);
         179                 : };
         180                 :
         181                 : template<>
         182                 : struct AlignedElem<4>
         183                 : {
         184                 :   MOZ_ALIGNED_DECL(uint8_t elem, 4);
         185                 : };
         186                 :
         187                 : template<>
         188                 : struct AlignedElem<8>
         189                 : {
         190                 :   MOZ_ALIGNED_DECL(uint8_t elem, 8);
         191                 : };
         192                 :
         193                 : template<>
         194                 : struct AlignedElem<16>
         195                 : {
         196                 :   MOZ_ALIGNED_DECL(uint8_t elem, 16);
         197                 : };
         198                 :
         199                 : /*
         200                 :  * This utility pales in comparison to Boost's aligned_storage. The utility
         201                 :  * simply assumes that uint64_t is enough alignment for anyone. This may need
         202                 :  * to be extended one day...
         203                 :  *
         204                 :  * As an important side effect, pulling the storage into this template is
         205                 :  * enough obfuscation to confuse gcc's strict-aliasing analysis into not giving
         206                 :  * false negatives when we cast from the char buffer to whatever type we've
         207                 :  * constructed using the bytes.
         208                 :  */
         209                 : template <size_t nbytes>
         210                 : struct AlignedStorage
         211                 : {
         212                 :     union U {
         213                 :         char bytes[nbytes];
         214                 :         uint64_t _;
         215                 :     } u;
         216                 :
         217       410803011 :     const void *addr() const { return u.bytes; }
         218        44366200 :     void *addr() { return u.bytes; }
         219                 : };
         220                 :
         221                 : template <class T>
         222                 : struct AlignedStorage2
         223                 : {
         224                 :     union U {
         225                 :         char bytes[sizeof(T)];
         226                 :         uint64_t _;
         227                 :     } u;
         228                 :
         229                 :     const T *addr() const { return (const T *)u.bytes; }
         230         3361169 :     T *addr() { return (T *)(void *)u.bytes; }
         231                 : };
         232                 :
         233                 : /*
         234                 :  * Small utility for lazily constructing objects without using dynamic storage.
         235                 :  * When a Maybe<T> is constructed, it is |empty()|, i.e., no value of T has
         236                 :  * been constructed and no T destructor will be called when the Maybe<T> is
         237                 :  * destroyed. Upon calling |construct|, a T object will be constructed with the
         238                 :  * given arguments and that object will be destroyed when the owning Maybe<T>
         239                 :  * is destroyed.
         240                 :  *
         241                 :  * N.B. GCC seems to miss some optimizations with Maybe and may generate extra
         242                 :  * branches/loads/stores. Use with caution on hot paths.
         243                 :  */
         244                 : template <class T>
         245                 : class Maybe
         246                 : {
         247                 :     AlignedStorage2<T> storage;
         248                 :     bool constructed;
         249                 :
         250         1914147 :     T &asT() { return *storage.addr(); }
         251                 :
         252                 :     explicit Maybe(const Maybe &other);
         253                 :     const Maybe &operator=(const Maybe &other);
         254                 :
         255                 :   public:
         256         8186407 :     Maybe() { constructed = false; }
         257         8186407 :     ~Maybe() { if (constructed) asT().~T(); }
         258                 :
         259          346091 :     bool empty() const { return !constructed; }
         260                 :
         261          210562 :     void construct() {
         262          210562 :         MOZ_ASSERT(!constructed);
         263          210562 :         new(storage.addr()) T();
         264          210562 :         constructed = true;
         265          210562 :     }
         266                 :
         267                 :     template <class T1>
         268            4167 :     void construct(const T1 &t1) {
         269            4167 :         MOZ_ASSERT(!constructed);
         270            4167 :         new(storage.addr()) T(t1);
         271            4167 :         constructed = true;
         272            4167 :     }
         273                 :
         274                 :     template <class T1, class T2>
         275         1232293 :     void construct(const T1 &t1, const T2 &t2) {
         276         1232293 :         MOZ_ASSERT(!constructed);
         277         1232293 :         new(storage.addr()) T(t1, t2);
         278         1232293 :         constructed = true;
         279         1232293 :     }
         280                 :
         281                 :     template <class T1, class T2, class T3>
         282                 :     void construct(const T1 &t1, const T2 &t2, const T3 &t3) {
         283                 :         MOZ_ASSERT(!constructed);
         284                 :         new(storage.addr()) T(t1, t2, t3);
         285                 :         constructed = true;
         286                 :     }
         287                 :
         288                 :     template <class T1, class T2, class T3, class T4>
         289                 :     void construct(const T1 &t1, const T2 &t2, const T3 &t3, const T4 &t4) {
         290                 :         MOZ_ASSERT(!constructed);
         291                 :         new(storage.addr()) T(t1, t2, t3, t4);
         292                 :         constructed = true;
         293                 :     }
         294                 :
         295              72 :     T *addr() {
         296              72 :         MOZ_ASSERT(constructed);
         297              72 :         return &asT();
         298                 :     }
         299                 :
         300          677615 :     T &ref() {
         301          677615 :         MOZ_ASSERT(constructed);
         302          677615 :         return asT();
         303                 :     }
         304                 :
         305                 :     const T &ref() const {
         306                 :         MOZ_ASSERT(constructed);
         307                 :         return const_cast<Maybe *>(this)->asT();
         308                 :     }
         309                 :
         310          210562 :     void destroy() {
         311          210562 :         ref().~T();
         312          210562 :         constructed = false;
         313          210562 :     }
         314                 :
         315           89042 :     void destroyIfConstructed() {
         316           89042 :         if (!empty())
         317             558 :             destroy();
         318           89042 :     }
         319                 : };
         320                 :
         321                 : /*
         322                 :  * Safely subtract two pointers when it is known that end >= begin.  This avoids
         323                 :  * the common compiler bug that if (size_t(end) - size_t(begin)) has the MSB
         324                 :  * set, the unsigned subtraction followed by right shift will produce -1, or
         325                 :  * size_t(-1), instead of the real difference.
         326                 :  */
         327                 : template <class T>
         328                 : MOZ_ALWAYS_INLINE size_t
         329        41301647 : PointerRangeSize(T* begin, T* end)
         330                 : {
         331        41301647 :     MOZ_ASSERT(end >= begin);
         332        41301647 :     return (size_t(end) - size_t(begin)) / sizeof(T);
         333                 : }
         334                 :
         335                 : /*
         336                 :  * Compute the length of an array with constant length.  (Use of this method
         337                 :  * with a non-array pointer will not compile.)
         338                 :  *
         339                 :  * Beware of the implicit trailing '\0' when using this with string constants.
         340                 :  */
         341                 : template<typename T, size_t N>
         342                 : size_t
         343        67974498 : ArrayLength(T (&arr)[N])
         344                 : {
         345        67974498 :     return N;
         346                 : }
         347                 :
         348                 : /*
         349                 :  * Compute the address one past the last element of a constant-length array.
         350                 :  *
         351                 :  * Beware of the implicit trailing '\0' when using this with string constants.
         352                 :  */
         353                 : template<typename T, size_t N>
         354                 : T*
         355           22118 : ArrayEnd(T (&arr)[N])
         356                 : {
         357           22118 :     return arr + ArrayLength(arr);
         358                 : }
         359                 :
         360                 : } /* namespace mozilla */
         361                 :
         362                 : #endif /* __cplusplus */
         363                 :
         364                 : #endif  /* mozilla_Util_h_ */

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