LCOV - code coverage report
Current view: directory - objdir/dist/include/mozilla - Util.h (source / functions) Found Hit Coverage
Test: app.info Lines: 62 56 90.3 %
Date: 2012-06-02 Functions: 466 269 57.7 %

       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               0 :     DebugOnly() {}
      80       246254409 :     DebugOnly(const T& other) : value(other) {}
      81                 :     DebugOnly(const DebugOnly& other) : value(other.value) {}
      82          167000 :     DebugOnly& operator=(const T& rhs) {
      83          167000 :         value = rhs;
      84          167000 :         return *this;
      85                 :     }
      86       495436358 :     void operator++(int) {
      87       495436358 :         value++;
      88       495436358 :     }
      89           52010 :     void operator--(int) {
      90           52010 :         value--;
      91           52010 :     }
      92                 : 
      93       549338810 :     operator T&() { return value; }
      94                 :     operator const T&() const { return value; }
      95                 : 
      96        21187703 :     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       246254378 :     ~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      1071926031 :     const void *addr() const { return u.bytes; }
     218        57015103 :     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        10352745 :     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         3732848 :     T &asT() { return *storage.addr(); }
     251                 : 
     252                 :     explicit Maybe(const Maybe &other);
     253                 :     const Maybe &operator=(const Maybe &other);
     254                 : 
     255                 :   public:
     256        14777697 :     Maybe() { constructed = false; }
     257        14777692 :     ~Maybe() { if (constructed) asT().~T(); }
     258                 : 
     259          389303 :     bool empty() const { return !constructed; }
     260                 : 
     261          260965 :     void construct() {
     262          260965 :         MOZ_ASSERT(!constructed);
     263          260965 :         new(storage.addr()) T();
     264          260965 :         constructed = true;
     265          260965 :     }
     266                 : 
     267                 :     template <class T1>
     268           32032 :     void construct(const T1 &t1) {
     269           32032 :         MOZ_ASSERT(!constructed);
     270           32032 :         new(storage.addr()) T(t1);
     271           32032 :         constructed = true;
     272           32032 :     }
     273                 : 
     274                 :     template <class T1, class T2>
     275         2862540 :     void construct(const T1 &t1, const T2 &t2) {
     276         2862540 :         MOZ_ASSERT(!constructed);
     277         2862540 :         new(storage.addr()) T(t1, t2);
     278         2862540 :         constructed = true;
     279         2862540 :     }
     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               0 :     void construct(const T1 &t1, const T2 &t2, const T3 &t3, const T4 &t4) {
     290               0 :         MOZ_ASSERT(!constructed);
     291               0 :         new(storage.addr()) T(t1, t2, t3, t4);
     292               0 :         constructed = true;
     293               0 :     }
     294                 : 
     295           55784 :     T *addr() {
     296           55784 :         MOZ_ASSERT(constructed);
     297           55784 :         return &asT();
     298                 :     }
     299                 : 
     300          782492 :     T &ref() {
     301          782492 :         MOZ_ASSERT(constructed);
     302          782492 :         return asT();
     303                 :     }
     304                 : 
     305                 :     const T &ref() const {
     306                 :         MOZ_ASSERT(constructed);
     307                 :         return const_cast<Maybe *>(this)->asT();
     308                 :     }
     309                 : 
     310          260965 :     void destroy() {
     311          260965 :         ref().~T();
     312          260965 :         constructed = false;
     313          260965 :     }
     314                 : 
     315          127756 :     void destroyIfConstructed() {
     316          127756 :         if (!empty())
     317            1219 :             destroy();
     318          127756 :     }
     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        48650217 : PointerRangeSize(T* begin, T* end)
     330                 : {
     331        48650217 :     MOZ_ASSERT(end >= begin);
     332        48650217 :     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       149315535 : ArrayLength(T (&arr)[N])
     344                 : {
     345       149315535 :     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         3627433 : ArrayEnd(T (&arr)[N])
     356                 : {
     357         3627433 :     return arr + ArrayLength(arr);
     358                 : }
     359                 : 
     360                 : } /* namespace mozilla */
     361                 : 
     362                 : #endif /* __cplusplus */
     363                 : 
     364                 : #endif  /* mozilla_Util_h_ */

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