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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 |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));
}
/**
* 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));
}
/*
* Determine whether the |N| elements at |one| are memory-identical to the
* |N| elements at |two|.
*/
template <class T, size_t N>
static MOZ_ALWAYS_INLINE bool
PodEqual(const T (&one)[N], const T (&two)[N])
{
return PodEqual(one, two, N);
}
} // namespace mozilla
#endif /* mozilla_PodOperations_h */
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