mfbt/Util.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * Miscellaneous uncategorized functionality.  Please add new functionality to
   9  * new headers, or to other appropriate existing headers, not here.
  10  */
  11
  12 #ifndef mozilla_Util_h
  13 #define mozilla_Util_h
  14
  15 #include "mozilla/Assertions.h"
  16 #include "mozilla/Attributes.h"
  17 #include "mozilla/Types.h"
  18
  19 #ifdef __cplusplus
  20
  21 #include "mozilla/Alignment.h"
  22
  23 namespace mozilla {
  24
  25 /*
  26  * Safely subtract two pointers when it is known that end >= begin.  This avoids
  27  * the common compiler bug that if (size_t(end) - size_t(begin)) has the MSB
  28  * set, the unsigned subtraction followed by right shift will produce -1, or
  29  * size_t(-1), instead of the real difference.
  30  */
  31 template<class T>
  32 MOZ_ALWAYS_INLINE size_t
  33 PointerRangeSize(T* begin, T* end)
  34 {
  35   MOZ_ASSERT(end >= begin);
  36   return (size_t(end) - size_t(begin)) / sizeof(T);
  37 }
  38
  39 /*
  40  * Compute the length of an array with constant length.  (Use of this method
  41  * with a non-array pointer will not compile.)
  42  *
  43  * Beware of the implicit trailing '\0' when using this with string constants.
  44  */
  45 template<typename T, size_t N>
  46 MOZ_CONSTEXPR size_t
  47 ArrayLength(T (&arr)[N])
  48 {
  49   return N;
  50 }
  51
  52 /*
  53  * Compute the address one past the last element of a constant-length array.
  54  *
  55  * Beware of the implicit trailing '\0' when using this with string constants.
  56  */
  57 template<typename T, size_t N>
  58 MOZ_CONSTEXPR T*
  59 ArrayEnd(T (&arr)[N])
  60 {
  61   return arr + ArrayLength(arr);
  62 }
  63
  64 } /* namespace mozilla */
  65
  66 #endif /* __cplusplus */
  67
  68 /*
  69  * MOZ_ARRAY_LENGTH() is an alternative to mozilla::ArrayLength() for C files
  70  * that can't use C++ template functions and for static_assert() calls that
  71  * can't call ArrayLength() when it is not a C++11 constexpr function.
  72  */
  73 #ifdef MOZ_HAVE_CXX11_CONSTEXPR
  74 #  define MOZ_ARRAY_LENGTH(array)   mozilla::ArrayLength(array)
  75 #else
  76 #  define MOZ_ARRAY_LENGTH(array)   (sizeof(array)/sizeof((array)[0]))
  77 #endif
  78
  79 #endif /* mozilla_Util_h */