DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (409f3966645a)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
 * Operations for zeroing POD types, arrays, and so on.
 *
 * These operations are preferable to memset, memcmp, and the like because they
 * don't require remembering to multiply by sizeof(T), array lengths, and so on
 * everywhere.
 */

#ifndef mozilla_PodOperations_h
#define mozilla_PodOperations_h

#include "mozilla/Array.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/Attributes.h"

#include <algorithm>
#include <stdint.h>
#include <string.h>

namespace mozilla {

/** Set the contents of |aT| to 0. */
template<typename T>
static MOZ_ALWAYS_INLINE void
PodZero(T* aT)
{
  memset(aT, 0, sizeof(T));
}

/** Set the contents of |aNElem| elements starting at |aT| to 0. */
template<typename T>
static MOZ_ALWAYS_INLINE void
PodZero(T* aT, size_t aNElem)
{
  /*
   * This function is often called with 'aNElem' small; we use an inline loop
   * instead of calling 'memset' with a non-constant length.  The compiler
   * should inline the memset call with constant size, though.
   */
  for (T* end = aT + aNElem; aT < end; aT++) {
    memset(aT, 0, sizeof(T));
  }
}

/*
 * Arrays implicitly convert to pointers to their first element, which is
 * dangerous when combined with the above PodZero definitions.  Adding an
 * overload for arrays is ambiguous, so we need another identifier.  The
 * ambiguous overload is left to catch mistaken uses of PodZero; if you get a
 * compile error involving PodZero and array types, use PodArrayZero instead.
 */
template<typename T, size_t N>
static void PodZero(T (&aT)[N]) = delete;
template<typename T, size_t N>
static void PodZero(T (&aT)[N], size_t aNElem) = delete;

/** Set the contents of the array |aT| to zero. */
template <class T, size_t N>
static MOZ_ALWAYS_INLINE void
PodArrayZero(T (&aT)[N])
{
  memset(aT, 0, N * sizeof(T));
}

template <typename T, size_t N>
static MOZ_ALWAYS_INLINE void
PodArrayZero(Array<T, N>& aArr)
{
  memset(&aArr[0], 0, N * sizeof(T));
}

/**
 * Assign |*aSrc| to |*aDst|.  The locations must not be the same and must not
 * overlap.
 */
template<typename T>
static MOZ_ALWAYS_INLINE void
PodAssign(T* aDst, const T* aSrc)
{
  MOZ_ASSERT(aDst + 1 <= aSrc || aSrc + 1 <= aDst,
             "destination and source must not overlap");
  memcpy(reinterpret_cast<char*>(aDst), reinterpret_cast<const char*>(aSrc),
         sizeof(T));
}

/**
 * Copy |aNElem| T elements from |aSrc| to |aDst|.  The two memory ranges must
 * not overlap!
 */
template<typename T>
static MOZ_ALWAYS_INLINE void
PodCopy(T* aDst, const T* aSrc, size_t aNElem)
{
  MOZ_ASSERT(aDst + aNElem <= aSrc || aSrc + aNElem <= aDst,
             "destination and source must not overlap");
  if (aNElem < 128) {
    /*
     * Avoid using operator= in this loop, as it may have been
     * intentionally deleted by the POD type.
     */
    for (const T* srcend = aSrc + aNElem; aSrc < srcend; aSrc++, aDst++) {
      PodAssign(aDst, aSrc);
    }
  } else {
    memcpy(aDst, aSrc, aNElem * sizeof(T));
  }
}

template<typename T>
static MOZ_ALWAYS_INLINE void
PodCopy(volatile T* aDst, const volatile T* aSrc, size_t aNElem)
{
  MOZ_ASSERT(aDst + aNElem <= aSrc || aSrc + aNElem <= aDst,
             "destination and source must not overlap");

  /*
   * Volatile |aDst| requires extra work, because it's undefined behavior to
   * modify volatile objects using the mem* functions.  Just write out the
   * loops manually, using operator= rather than memcpy for the same reason,
   * and let the compiler optimize to the extent it can.
   */
  for (const volatile T* srcend = aSrc + aNElem;
       aSrc < srcend;
       aSrc++, aDst++) {
    *aDst = *aSrc;
  }
}

/*
 * Copy the contents of the array |aSrc| into the array |aDst|, both of size N.
 * The arrays must not overlap!
 */
template <class T, size_t N>
static MOZ_ALWAYS_INLINE void
PodArrayCopy(T (&aDst)[N], const T (&aSrc)[N])
{
  PodCopy(aDst, aSrc, N);
}

/**
 * Copy the memory for |aNElem| T elements from |aSrc| to |aDst|.  If the two
 * memory ranges overlap, then the effect is as if the |aNElem| elements are
 * first copied from |aSrc| to a temporary array, and then from the temporary
 * array to |aDst|.
 */
template<typename T>
static MOZ_ALWAYS_INLINE void
PodMove(T* aDst, const T* aSrc, size_t aNElem)
{
  MOZ_ASSERT(aNElem <= SIZE_MAX / sizeof(T),
             "trying to move an impossible number of elements");
  memmove(aDst, aSrc, aNElem * sizeof(T));
}

/**
 * Looking for a PodEqual? Use ArrayEqual from ArrayUtils.h.
 * Note that we *cannot* use memcmp for this, due to padding bytes, etc..
 */

} // namespace mozilla

#endif /* mozilla_PodOperations_h */