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/* -*- Mode: C++; tab-width: 2; 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/Attributes.h"
#include "mozilla/Util.h"
#include <string.h>
namespace mozilla {
/** Set the contents of |t| to 0. */
template<typename T>
static void
PodZero(T* t)
{
memset(t, 0, sizeof(T));
}
/** Set the contents of |nelem| elements starting at |t| to 0. */
template<typename T>
static 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 void
PodArrayZero(T (&t)[N])
{
memset(t, 0, N * sizeof(T));
}
/**
* Assign |*src| to |*dst|. The locations must not be the same and must not
* overlap.
*/
template<typename T>
static 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>
MOZ_ALWAYS_INLINE static 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>
MOZ_ALWAYS_INLINE static 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 void
PodArrayCopy(T (&dst)[N], const T (&src)[N])
{
PodCopy(dst, src, N);
}
/**
* Determine whether the |len| elements at |one| are memory-identical to the
* |len| elements at |two|.
*/
template<typename T>
MOZ_ALWAYS_INLINE static 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_
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