mirror of
https://github.com/mozilla/gecko-dev.git
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9439ff268e
--HG-- extra : rebase_source : 98d2557c7fe4648d79143c654e7e31767fca2e65
196 lines
5.5 KiB
C++
196 lines
5.5 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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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/Array.h"
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#include "mozilla/ArrayUtils.h"
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#include "mozilla/Attributes.h"
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#include <stdint.h>
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#include <string.h>
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namespace mozilla {
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/** Set the contents of |aT| to 0. */
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template<typename T>
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static MOZ_ALWAYS_INLINE void
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PodZero(T* aT)
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{
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memset(aT, 0, sizeof(T));
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}
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/** Set the contents of |aNElem| elements starting at |aT| to 0. */
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template<typename T>
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static MOZ_ALWAYS_INLINE void
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PodZero(T* aT, size_t aNElem)
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{
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/*
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* This function is often called with 'aNElem' 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 = aT + aNElem; aT < end; aT++) {
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memset(aT, 0, sizeof(T));
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}
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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 (&aT)[N]) MOZ_DELETE;
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template<typename T, size_t N>
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static void PodZero(T (&aT)[N], size_t aNElem) MOZ_DELETE;
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/** Set the contents of the array |aT| to zero. */
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template <class T, size_t N>
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static MOZ_ALWAYS_INLINE void
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PodArrayZero(T (&aT)[N])
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{
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memset(aT, 0, N * sizeof(T));
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}
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template <typename T, size_t N>
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static MOZ_ALWAYS_INLINE void
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PodArrayZero(Array<T, N>& aArr)
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{
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memset(&aArr[0], 0, N * sizeof(T));
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}
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/**
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* Assign |*aSrc| to |*aDst|. 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 MOZ_ALWAYS_INLINE void
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PodAssign(T* aDst, const T* aSrc)
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{
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MOZ_ASSERT(aDst != aSrc);
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MOZ_ASSERT_IF(aSrc < aDst,
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PointerRangeSize(aSrc, static_cast<const T*>(aDst)) >= 1);
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MOZ_ASSERT_IF(aDst < aSrc,
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PointerRangeSize(static_cast<const T*>(aDst), aSrc) >= 1);
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memcpy(reinterpret_cast<char*>(aDst), reinterpret_cast<const char*>(aSrc),
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sizeof(T));
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}
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/**
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* Copy |aNElem| T elements from |aSrc| to |aDst|. The two memory ranges must
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* not overlap!
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*/
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template<typename T>
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static MOZ_ALWAYS_INLINE void
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PodCopy(T* aDst, const T* aSrc, size_t aNElem)
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{
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MOZ_ASSERT(aDst != aSrc);
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MOZ_ASSERT_IF(aSrc < aDst,
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PointerRangeSize(aSrc, static_cast<const T*>(aDst)) >= aNElem);
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MOZ_ASSERT_IF(aDst < aSrc,
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PointerRangeSize(static_cast<const T*>(aDst), aSrc) >= aNElem);
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if (aNElem < 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 = aSrc + aNElem; aSrc < srcend; aSrc++, aDst++) {
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PodAssign(aDst, aSrc);
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}
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} else {
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memcpy(aDst, aSrc, aNElem * sizeof(T));
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}
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}
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template<typename T>
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static MOZ_ALWAYS_INLINE void
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PodCopy(volatile T* aDst, const volatile T* aSrc, size_t aNElem)
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{
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MOZ_ASSERT(aDst != aSrc);
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MOZ_ASSERT_IF(aSrc < aDst,
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PointerRangeSize(aSrc, static_cast<const volatile T*>(aDst)) >= aNElem);
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MOZ_ASSERT_IF(aDst < aSrc,
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PointerRangeSize(static_cast<const volatile T*>(aDst), aSrc) >= aNElem);
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/*
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* Volatile |aDst| requires extra work, because it's undefined behavior to
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* modify volatile objects using the mem* functions. Just write out the
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* loops manually, using operator= rather than memcpy for the same reason,
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* and let the compiler optimize to the extent it can.
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*/
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for (const volatile T* srcend = aSrc + aNElem;
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aSrc < srcend;
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aSrc++, aDst++) {
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*aDst = *aSrc;
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}
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}
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/*
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* Copy the contents of the array |aSrc| into the array |aDst|, both of size N.
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* The arrays must not overlap!
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*/
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template <class T, size_t N>
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static MOZ_ALWAYS_INLINE void
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PodArrayCopy(T (&aDst)[N], const T (&aSrc)[N])
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{
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PodCopy(aDst, aSrc, N);
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}
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/**
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* Copy the memory for |aNElem| T elements from |aSrc| to |aDst|. If the two
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* memory ranges overlap, then the effect is as if the |aNElem| elements are
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* first copied from |aSrc| to a temporary array, and then from the temporary
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* array to |aDst|.
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*/
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template<typename T>
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static MOZ_ALWAYS_INLINE void
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PodMove(T* aDst, const T* aSrc, size_t aNElem)
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{
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MOZ_ASSERT(aNElem <= SIZE_MAX / sizeof(T),
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"trying to move an impossible number of elements");
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memmove(aDst, aSrc, aNElem * sizeof(T));
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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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static MOZ_ALWAYS_INLINE 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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}
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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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