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129 lines
3.5 KiB
C++
129 lines
3.5 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* Operations for zeroing POD types, arrays, and so on.
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*
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* These operations are preferable to memset, memcmp, and the like because they
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* don't require remembering to multiply by sizeof(T), array lengths, and so on
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* everywhere.
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*/
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#ifndef mozilla_PodOperations_h
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#define mozilla_PodOperations_h
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#include "mozilla/Attributes.h"
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#include "mozilla/Util.h"
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#include <string.h>
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namespace mozilla {
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/** Set the contents of |t| to 0. */
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template<typename T>
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static void
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PodZero(T* t)
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{
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memset(t, 0, sizeof(T));
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}
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/** Set the contents of |nelem| elements starting at |t| to 0. */
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template<typename T>
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static void
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PodZero(T* t, size_t nelem)
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{
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/*
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* This function is often called with 'nelem' small; we use an inline loop
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* instead of calling 'memset' with a non-constant length. The compiler
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* should inline the memset call with constant size, though.
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*/
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for (T* end = t + nelem; t < end; t++)
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memset(t, 0, sizeof(T));
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}
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/*
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* Arrays implicitly convert to pointers to their first element, which is
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* dangerous when combined with the above PodZero definitions. Adding an
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* overload for arrays is ambiguous, so we need another identifier. The
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* ambiguous overload is left to catch mistaken uses of PodZero; if you get a
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* compile error involving PodZero and array types, use PodArrayZero instead.
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*/
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template<typename T, size_t N>
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static void PodZero(T (&t)[N]) MOZ_DELETE;
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template<typename T, size_t N>
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static void PodZero(T (&t)[N], size_t nelem) MOZ_DELETE;
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/** Set the contents of the array |t| to zero. */
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template <class T, size_t N>
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static void
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PodArrayZero(T (&t)[N])
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{
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memset(t, 0, N * sizeof(T));
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}
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/**
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* Assign |*src| to |*dst|. The locations must not be the same and must not
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* overlap.
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*/
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template<typename T>
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static void
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PodAssign(T* dst, const T* src)
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{
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MOZ_ASSERT(dst != src);
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MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= 1);
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MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= 1);
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memcpy(reinterpret_cast<char*>(dst), reinterpret_cast<const char*>(src), sizeof(T));
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}
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/**
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* Copy |nelem| T elements from |src| to |dst|. The two memory ranges must not
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* overlap!
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*/
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template<typename T>
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MOZ_ALWAYS_INLINE static void
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PodCopy(T* dst, const T* src, size_t nelem)
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{
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MOZ_ASSERT(dst != src);
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MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= nelem);
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MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= nelem);
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if (nelem < 128) {
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/*
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* Avoid using operator= in this loop, as it may have been
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* intentionally deleted by the POD type.
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*/
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for (const T* srcend = src + nelem; src < srcend; src++, dst++)
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PodAssign(dst, src);
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} else {
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memcpy(dst, src, nelem * sizeof(T));
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}
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}
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/**
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* Determine whether the |len| elements at |one| are memory-identical to the
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* |len| elements at |two|.
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*/
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template<typename T>
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MOZ_ALWAYS_INLINE static bool
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PodEqual(const T* one, const T* two, size_t len)
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{
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if (len < 128) {
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const T* p1end = one + len;
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const T* p1 = one;
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const T* p2 = two;
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for (; p1 < p1end; p1++, p2++) {
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if (*p1 != *p2)
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return false;
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}
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return true;
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}
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return !memcmp(one, two, len * sizeof(T));
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}
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} // namespace mozilla
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#endif // mozilla_PodOperations_h_
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