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 /* -*- 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 <stdint.h>

 #include <string.h>

 namespace mozilla {

 /** Set the contents of |t| to 0. */

 template<typename T>

 static MOZ_ALWAYS_INLINE void

 PodZero(T* t)

 {

   memset(t, 0, sizeof(T));

 }

 /** Set the contents of |nelem| elements starting at |t| to 0. */

 template<typename T>

 static MOZ_ALWAYS_INLINE void

 PodZero(T* t, size_t nelem)

 {

   /*

    * This function is often called with 'nelem' 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 = t + nelem; t < end; t++)

     memset(t, 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 (&t)[N]) MOZ_DELETE;

 template<typename T, size_t N>

 static void PodZero(T (&t)[N], size_t nelem) MOZ_DELETE;

 /** Set the contents of the array |t| to zero. */

 template <class T, size_t N>

 static MOZ_ALWAYS_INLINE void

 PodArrayZero(T (&t)[N])

 {

   memset(t, 0, N * sizeof(T));

 }

 template <typename T, size_t N>

 static MOZ_ALWAYS_INLINE void

 PodArrayZero(Array<T, N>& arr)

 {

   memset(&arr[0], 0, N * sizeof(T));

 }

 /**

  * Assign |*src| to |*dst|.  The locations must not be the same and must not

  * overlap.

  */

 template<typename T>

 static MOZ_ALWAYS_INLINE void

 PodAssign(T* dst, const T* src)

 {

   MOZ_ASSERT(dst != src);

   MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= 1);

   MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= 1);

   memcpy(reinterpret_cast<char*>(dst), reinterpret_cast<const char*>(src), sizeof(T));

 }

 /**

  * Copy |nelem| T elements from |src| to |dst|.  The two memory ranges must not

  * overlap!

  */

 template<typename T>

 static MOZ_ALWAYS_INLINE void

 PodCopy(T* dst, const T* src, size_t nelem)

 {

   MOZ_ASSERT(dst != src);

   MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= nelem);

   MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= nelem);

   if (nelem < 128) {

     /*

      * Avoid using operator= in this loop, as it may have been

      * intentionally deleted by the POD type.

      */

     for (const T* srcend = src + nelem; src < srcend; src++, dst++)

       PodAssign(dst, src);

   } else {

     memcpy(dst, src, nelem * sizeof(T));

   }

 }

 template<typename T>

 static MOZ_ALWAYS_INLINE void

 PodCopy(volatile T* dst, const volatile T* src, size_t nelem)

 {

   MOZ_ASSERT(dst != src);

   MOZ_ASSERT_IF(src < dst,

                 PointerRangeSize(src, static_cast<const volatile T*>(dst)) >= nelem);

   MOZ_ASSERT_IF(dst < src,

                 PointerRangeSize(static_cast<const volatile T*>(dst), src) >= nelem);

   /*

    * Volatile |dst| 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 = src + nelem; src < srcend; src++, dst++)

     *dst = *src;

 }

 /*

  * Copy the contents of the array |src| into the array |dst|, both of size N.

  * The arrays must not overlap!

  */

 template <class T, size_t N>

 static MOZ_ALWAYS_INLINE void

 PodArrayCopy(T (&dst)[N], const T (&src)[N])

 {

   PodCopy(dst, src, N);

 }

 /**

  * Copy the memory for |nelem| T elements from |src| to |dst|.  If the two

  * memory ranges overlap, then the effect is as if the |nelem| elements are

  * first copied from |src| to a temporary array, and then from the temporary

  * array to |dst|.

  */

 template<typename T>

 static MOZ_ALWAYS_INLINE void

 PodMove(T* dst, const T* src, size_t nelem)

 {

   MOZ_ASSERT(nelem <= SIZE_MAX / sizeof(T),

              "trying to move an impossible number of elements");

   memmove(dst, src, nelem * sizeof(T));

 }

 /**

  * Determine whether the |len| elements at |one| are memory-identical to the

  * |len| elements at |two|.

  */

 template<typename T>

 static MOZ_ALWAYS_INLINE bool

 PodEqual(const T* one, const T* two, size_t len)

 {

   if (len < 128) {

     const T* p1end = one + len;

     const T* p1 = one;

     const T* p2 = two;

     for (; p1 < p1end; p1++, p2++) {

       if (*p1 != *p2)

         return false;

     }

     return true;

   }

   return !memcmp(one, two, len * sizeof(T));

 }

 } // namespace mozilla

 #endif /* mozilla_PodOperations_h */