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Diffstat (limited to 'mfbt/Span.h')
| -rw-r--r-- | mfbt/Span.h | 1041 |
1 files changed, 1041 insertions, 0 deletions
diff --git a/mfbt/Span.h b/mfbt/Span.h new file mode 100644 index 000000000..f031a928b --- /dev/null +++ b/mfbt/Span.h @@ -0,0 +1,1041 @@ +/////////////////////////////////////////////////////////////////////////////// +// +// Copyright (c) 2015 Microsoft Corporation. All rights reserved. +// +// This code is licensed under the MIT License (MIT). +// +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +// THE SOFTWARE. +// +/////////////////////////////////////////////////////////////////////////////// + +// Adapted from https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/include/gsl/span +// and https://github.com/Microsoft/GSL/blob/3819df6e378ffccf0e29465afe99c3b324c2aa70/include/gsl/gsl_util + +#ifndef mozilla_Span_h +#define mozilla_Span_h + +#include "mozilla/Array.h" +#include "mozilla/Assertions.h" +#include "mozilla/Casting.h" +#include "mozilla/IntegerTypeTraits.h" +#include "mozilla/Move.h" +#include "mozilla/TypeTraits.h" +#include "mozilla/UniquePtr.h" + +#include <algorithm> +#include <array> +#include <cstring> +#include <iterator> + +// Classifications for reasons why constexpr was removed in C++14 to C++11 +// conversion. Once we upgrade compilers, we can try defining each of these +// to constexpr to restore a category of constexprs at a time. +#define MOZ_SPAN_ASSERTION_CONSTEXPR +#define MOZ_SPAN_GCC_CONSTEXPR +#define MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR +#define MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN +#define MOZ_SPAN_NON_CONST_CONSTEXPR + +#ifdef _MSC_VER +#pragma warning(push) + +// turn off some warnings that are noisy about our MOZ_RELEASE_ASSERT statements +#pragma warning(disable : 4127) // conditional expression is constant + +// blanket turn off warnings from CppCoreCheck for now +// so people aren't annoyed by them when running the tool. +// more targeted suppressions will be added in a future update to the GSL +#pragma warning(disable : 26481 26482 26483 26485 26490 26491 26492 26493 26495) + +#if _MSC_VER < 1910 +#pragma push_macro("constexpr") +#define constexpr /*constexpr*/ + +#endif // _MSC_VER < 1910 +#endif // _MSC_VER + +namespace mozilla { + +// Stuff from gsl_util + +// narrow_cast(): a searchable way to do narrowing casts of values +template<class T, class U> +inline constexpr T +narrow_cast(U&& u) +{ + return static_cast<T>(mozilla::Forward<U>(u)); +} + +// end gsl_util + +// [views.constants], constants +// This was -1 in gsl::span, but using size_t for sizes instead of ptrdiff_t +// and reserving a magic value that realistically doesn't occur in +// compile-time-constant Span sizes makes things a lot less messy in terms of +// comparison between signed and unsigned. +constexpr const size_t dynamic_extent = mozilla::MaxValue<size_t>::value; + +template<class ElementType, size_t Extent = dynamic_extent> +class Span; + +// implementation details +namespace span_details { + +// C++14 types that we don't have because we build as C++11. +template<class T> +using remove_cv_t = typename mozilla::RemoveCV<T>::Type; +template<class T> +using remove_const_t = typename mozilla::RemoveConst<T>::Type; +template<bool B, class T, class F> +using conditional_t = typename mozilla::Conditional<B, T, F>::Type; +template<class T> +using add_pointer_t = typename mozilla::AddPointer<T>::Type; +template<bool B, class T = void> +using enable_if_t = typename mozilla::EnableIf<B, T>::Type; + +template<class T> +struct is_span_oracle : mozilla::FalseType +{ +}; + +template<class ElementType, size_t Extent> +struct is_span_oracle<mozilla::Span<ElementType, Extent>> : mozilla::TrueType +{ +}; + +template<class T> +struct is_span : public is_span_oracle<remove_cv_t<T>> +{ +}; + +template<class T> +struct is_std_array_oracle : mozilla::FalseType +{ +}; + +template<class ElementType, size_t Extent> +struct is_std_array_oracle<std::array<ElementType, Extent>> : mozilla::TrueType +{ +}; + +template<class T> +struct is_std_array : public is_std_array_oracle<remove_cv_t<T>> +{ +}; + +template<size_t From, size_t To> +struct is_allowed_extent_conversion + : public mozilla::IntegralConstant<bool, + From == To || + From == mozilla::dynamic_extent || + To == mozilla::dynamic_extent> +{ +}; + +template<class From, class To> +struct is_allowed_element_type_conversion + : public mozilla::IntegralConstant<bool, mozilla::IsConvertible<From (*)[], To (*)[]>::value> +{ +}; + +template<class Span, bool IsConst> +class span_iterator +{ + using element_type_ = typename Span::element_type; + +public: + using iterator_category = std::random_access_iterator_tag; + using value_type = remove_const_t<element_type_>; + using difference_type = typename Span::index_type; + + using reference = conditional_t<IsConst, const element_type_, element_type_>&; + using pointer = add_pointer_t<reference>; + + constexpr span_iterator() : span_iterator(nullptr, 0) {} + + MOZ_SPAN_ASSERTION_CONSTEXPR span_iterator(const Span* span, + typename Span::index_type index) + : span_(span) + , index_(index) + { + MOZ_RELEASE_ASSERT(span == nullptr || + (index_ >= 0 && index <= span_->Length())); + } + + friend class span_iterator<Span, true>; + constexpr MOZ_IMPLICIT span_iterator(const span_iterator<Span, false>& other) + : span_iterator(other.span_, other.index_) + { + } + + MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR span_iterator<Span, IsConst>& + operator=(const span_iterator<Span, IsConst>&) = default; + + MOZ_SPAN_GCC_CONSTEXPR reference operator*() const + { + MOZ_RELEASE_ASSERT(span_); + return (*span_)[index_]; + } + + MOZ_SPAN_GCC_CONSTEXPR pointer operator->() const + { + MOZ_RELEASE_ASSERT(span_); + return &((*span_)[index_]); + } + + MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator& operator++() + { + MOZ_RELEASE_ASSERT(span_ && index_ >= 0 && index_ < span_->Length()); + ++index_; + return *this; + } + + MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator operator++(int) + { + auto ret = *this; + ++(*this); + return ret; + } + + MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator& operator--() + { + MOZ_RELEASE_ASSERT(span_ && index_ > 0 && index_ <= span_->Length()); + --index_; + return *this; + } + + MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator operator--(int) + { + auto ret = *this; + --(*this); + return ret; + } + + MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN span_iterator + operator+(difference_type n) const + { + auto ret = *this; + return ret += n; + } + + MOZ_SPAN_GCC_CONSTEXPR span_iterator& operator+=(difference_type n) + { + MOZ_RELEASE_ASSERT(span_ && (index_ + n) >= 0 && + (index_ + n) <= span_->Length()); + index_ += n; + return *this; + } + + MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN span_iterator + operator-(difference_type n) const + { + auto ret = *this; + return ret -= n; + } + + MOZ_SPAN_NON_CONST_CONSTEXPR span_iterator& operator-=(difference_type n) + + { + return *this += -n; + } + + MOZ_SPAN_GCC_CONSTEXPR difference_type + operator-(const span_iterator& rhs) const + { + MOZ_RELEASE_ASSERT(span_ == rhs.span_); + return index_ - rhs.index_; + } + + constexpr reference operator[](difference_type n) const + { + return *(*this + n); + } + + constexpr friend bool operator==(const span_iterator& lhs, + const span_iterator& rhs) + { + return lhs.span_ == rhs.span_ && lhs.index_ == rhs.index_; + } + + constexpr friend bool operator!=(const span_iterator& lhs, + const span_iterator& rhs) + { + return !(lhs == rhs); + } + + MOZ_SPAN_GCC_CONSTEXPR friend bool operator<(const span_iterator& lhs, + const span_iterator& rhs) + { + MOZ_RELEASE_ASSERT(lhs.span_ == rhs.span_); + return lhs.index_ < rhs.index_; + } + + MOZ_SPAN_GCC_CONSTEXPR friend bool operator<=(const span_iterator& lhs, + const span_iterator& rhs) + { + return !(rhs < lhs); + } + + MOZ_SPAN_GCC_CONSTEXPR friend bool operator>(const span_iterator& lhs, + const span_iterator& rhs) + { + return rhs < lhs; + } + + MOZ_SPAN_GCC_CONSTEXPR friend bool operator>=(const span_iterator& lhs, + const span_iterator& rhs) + { + return !(rhs > lhs); + } + + void swap(span_iterator& rhs) + { + std::swap(index_, rhs.index_); + std::swap(span_, rhs.span_); + } + +protected: + const Span* span_; + size_t index_; +}; + +template<class Span, bool IsConst> +inline constexpr span_iterator<Span, IsConst> +operator+(typename span_iterator<Span, IsConst>::difference_type n, + const span_iterator<Span, IsConst>& rhs) +{ + return rhs + n; +} + +template<size_t Ext> +class extent_type +{ +public: + using index_type = size_t; + + static_assert(Ext >= 0, "A fixed-size Span must be >= 0 in size."); + + constexpr extent_type() {} + + template<index_type Other> + MOZ_SPAN_ASSERTION_CONSTEXPR MOZ_IMPLICIT extent_type(extent_type<Other> ext) + { + static_assert( + Other == Ext || Other == dynamic_extent, + "Mismatch between fixed-size extent and size of initializing data."); + MOZ_RELEASE_ASSERT(ext.size() == Ext); + } + + MOZ_SPAN_ASSERTION_CONSTEXPR MOZ_IMPLICIT extent_type(index_type length) + { + MOZ_RELEASE_ASSERT(length == Ext); + } + + constexpr index_type size() const { return Ext; } +}; + +template<> +class extent_type<dynamic_extent> +{ +public: + using index_type = size_t; + + template<index_type Other> + explicit constexpr extent_type(extent_type<Other> ext) + : size_(ext.size()) + { + } + + explicit constexpr extent_type(index_type length) + : size_(length) + { + } + + constexpr index_type size() const { return size_; } + +private: + index_type size_; +}; +} // namespace span_details + +/** + * Span - slices for C++ + * + * Span implements Rust's slice concept for C++. It's called "Span" instead of + * "Slice" to follow the naming used in C++ Core Guidelines. + * + * A Span wraps a pointer and a length that identify a non-owning view to a + * contiguous block of memory of objects of the same type. Various types, + * including (pre-decay) C arrays, XPCOM strings, nsTArray, mozilla::Array, + * mozilla::Range and contiguous standard-library containers, auto-convert + * into Spans when attempting to pass them as arguments to methods that take + * Spans. MakeSpan() functions can be used for explicit conversion in other + * contexts. (Span itself autoconverts into mozilla::Range.) + * + * Like Rust's slices, Span provides safety against out-of-bounds access by + * performing run-time bound checks. However, unlike Rust's slices, Span + * cannot provide safety against use-after-free. + * + * (Note: Span is like Rust's slice only conceptually. Due to the lack of + * ABI guarantees, you should still decompose spans/slices to raw pointer + * and length parts when crossing the FFI.) + * + * In addition to having constructors and MakeSpan() functions that take + * various well-known types, a Span for an arbitrary type can be constructed + * (via constructor or MakeSpan()) from a pointer and a length or a pointer + * and another pointer pointing just past the last element. + * + * A Span<const char> can be obtained for const char* pointing to a + * zero-terminated C string using the MakeCStringSpan() function. A + * corresponding implicit constructor does not exist in order to avoid + * accidental construction in cases where const char* does not point to a + * zero-terminated C string. + * + * Span has methods that follow the Mozilla naming style and methods that + * don't. The methods that follow the Mozilla naming style are meant to be + * used directly from Mozilla code. The methods that don't are meant for + * integration with C++11 range-based loops and with meta-programming that + * expects the same methods that are found on the standard-library + * containers. For example, to decompose a Span into its parts in Mozilla + * code, use Elements() and Length() (as with nsTArray) instead of data() + * and size() (as with std::vector). + * + * The pointer and length wrapped by a Span cannot be changed after a Span has + * been created. When new values are required, simply create a new Span. Span + * has a method called Subspan() that works analogously to the Substring() + * method of XPCOM strings taking a start index and an optional length. As a + * Mozilla extension (relative to Microsoft's gsl::span that mozilla::Span is + * based on), Span has methods From(start), To(end) and FromTo(start, end) + * that correspond to Rust's &slice[start..], &slice[..end] and + * &slice[start..end], respectively. (That is, the end index is the index of + * the first element not to be included in the new subspan.) + * + * When indicating a Span that's only read from, const goes inside the type + * parameter. Don't put const in front of Span. That is: + * size_t ReadsFromOneSpanAndWritesToAnother(Span<const uint8_t> aReadFrom, + * Span<uint8_t> aWrittenTo); + * + * Any Span<const T> can be viewed as Span<const uint8_t> using the function + * AsBytes(). Any Span<T> can be viewed as Span<uint8_t> using the function + * AsWritableBytes(). + */ +template<class ElementType, size_t Extent> +class Span +{ +public: + // constants and types + using element_type = ElementType; + using index_type = size_t; + using pointer = element_type*; + using reference = element_type&; + + using iterator = + span_details::span_iterator<Span<ElementType, Extent>, false>; + using const_iterator = + span_details::span_iterator<Span<ElementType, Extent>, true>; + using reverse_iterator = std::reverse_iterator<iterator>; + using const_reverse_iterator = std::reverse_iterator<const_iterator>; + + constexpr static const index_type extent = Extent; + + // [Span.cons], Span constructors, copy, assignment, and destructor + // "Dependent" is needed to make "span_details::enable_if_t<(Dependent || Extent == 0 || Extent == mozilla::MaxValue<size_t>::value)>" SFINAE, + // since "span_details::enable_if_t<(Extent == 0 || Extent == mozilla::MaxValue<size_t>::value)>" is ill-formed when Extent is neither of the extreme values. + /** + * Constructor with no args. + */ + template< + bool Dependent = false, + class = span_details::enable_if_t< + (Dependent || Extent == 0 || Extent == mozilla::MaxValue<size_t>::value)>> + constexpr Span() + : storage_(nullptr, span_details::extent_type<0>()) + { + } + + /** + * Constructor for nullptr. + */ + constexpr MOZ_IMPLICIT Span(std::nullptr_t) : Span() {} + + /** + * Constructor for pointer and length. + */ + constexpr Span(pointer aPtr, index_type aLength) + : storage_(aPtr, aLength) + { + } + + /** + * Constructor for start pointer and pointer past end. + */ + constexpr Span(pointer aStartPtr, pointer aEndPtr) + : storage_(aStartPtr, std::distance(aStartPtr, aEndPtr)) + { + } + + /** + * Constructor for C array. + */ + template<size_t N> + constexpr MOZ_IMPLICIT Span(element_type (&aArr)[N]) + : storage_(&aArr[0], span_details::extent_type<N>()) + { + } + + /** + * Constructor for std::array. + */ + template<size_t N, + class ArrayElementType = span_details::remove_const_t<element_type>> + constexpr MOZ_IMPLICIT Span(std::array<ArrayElementType, N>& aArr) + : storage_(&aArr[0], span_details::extent_type<N>()) + { + } + + /** + * Constructor for const std::array. + */ + template<size_t N> + constexpr MOZ_IMPLICIT Span( + const std::array<span_details::remove_const_t<element_type>, N>& aArr) + : storage_(&aArr[0], span_details::extent_type<N>()) + { + } + + /** + * Constructor for mozilla::Array. + */ + template<size_t N, + class ArrayElementType = span_details::remove_const_t<element_type>> + constexpr MOZ_IMPLICIT Span(mozilla::Array<ArrayElementType, N>& aArr) + : storage_(&aArr[0], span_details::extent_type<N>()) + { + } + + /** + * Constructor for const mozilla::Array. + */ + template<size_t N> + constexpr MOZ_IMPLICIT Span( + const mozilla::Array<span_details::remove_const_t<element_type>, N>& aArr) + : storage_(&aArr[0], span_details::extent_type<N>()) + { + } + + /** + * Constructor for mozilla::UniquePtr holding an array and length. + */ + template<class ArrayElementType = std::add_pointer<element_type>> + constexpr Span(const mozilla::UniquePtr<ArrayElementType>& aPtr, + index_type aLength) + : storage_(aPtr.get(), aLength) + { + } + + // NB: the SFINAE here uses .data() as a incomplete/imperfect proxy for the requirement + // on Container to be a contiguous sequence container. + /** + * Constructor for standard-library containers. + */ + template< + class Container, + class = span_details::enable_if_t< + !span_details::is_span<Container>::value && + !span_details::is_std_array<Container>::value && + mozilla::IsConvertible<typename Container::pointer, pointer>::value && + mozilla::IsConvertible<typename Container::pointer, + decltype(mozilla::DeclVal<Container>().data())>::value>> + constexpr MOZ_IMPLICIT Span(Container& cont) + : Span(cont.data(), ReleaseAssertedCast<index_type>(cont.size())) + { + } + + /** + * Constructor for standard-library containers (const version). + */ + template< + class Container, + class = span_details::enable_if_t< + mozilla::IsConst<element_type>::value && + !span_details::is_span<Container>::value && + mozilla::IsConvertible<typename Container::pointer, pointer>::value && + mozilla::IsConvertible<typename Container::pointer, + decltype(mozilla::DeclVal<Container>().data())>::value>> + constexpr MOZ_IMPLICIT Span(const Container& cont) + : Span(cont.data(), ReleaseAssertedCast<index_type>(cont.size())) + { + } + + /** + * Constructor from other Span. + */ + constexpr Span(const Span& other) = default; + + /** + * Constructor from other Span. + */ + constexpr Span(Span&& other) = default; + + /** + * Constructor from other Span with conversion of element type. + */ + template< + class OtherElementType, + size_t OtherExtent, + class = span_details::enable_if_t< + span_details::is_allowed_extent_conversion<OtherExtent, Extent>::value && + span_details::is_allowed_element_type_conversion<OtherElementType, + element_type>::value>> + constexpr MOZ_IMPLICIT Span(const Span<OtherElementType, OtherExtent>& other) + : storage_(other.data(), + span_details::extent_type<OtherExtent>(other.size())) + { + } + + /** + * Constructor from other Span with conversion of element type. + */ + template< + class OtherElementType, + size_t OtherExtent, + class = span_details::enable_if_t< + span_details::is_allowed_extent_conversion<OtherExtent, Extent>::value && + span_details::is_allowed_element_type_conversion<OtherElementType, + element_type>::value>> + constexpr MOZ_IMPLICIT Span(Span<OtherElementType, OtherExtent>&& other) + : storage_(other.data(), + span_details::extent_type<OtherExtent>(other.size())) + { + } + + ~Span() = default; + MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR Span& operator=(const Span& other) + = default; + + MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR Span& operator=(Span&& other) + = default; + + // [Span.sub], Span subviews + /** + * Subspan with first N elements with compile-time N. + */ + template<size_t Count> + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, Count> First() const + { + MOZ_RELEASE_ASSERT(Count <= size()); + return { data(), Count }; + } + + /** + * Subspan with last N elements with compile-time N. + */ + template<size_t Count> + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, Count> Last() const + { + MOZ_RELEASE_ASSERT(Count <= size()); + return { data() + (size() - Count), Count }; + } + + /** + * Subspan with compile-time start index and length. + */ + template<size_t Offset, size_t Count = dynamic_extent> + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, Count> Subspan() const + { + MOZ_RELEASE_ASSERT(Offset <= size() && + (Count == dynamic_extent || (Offset + Count <= size()))); + return { data() + Offset, + Count == dynamic_extent ? size() - Offset : Count }; + } + + /** + * Subspan with first N elements with run-time N. + */ + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> First( + index_type aCount) const + { + MOZ_RELEASE_ASSERT(aCount <= size()); + return { data(), aCount }; + } + + /** + * Subspan with last N elements with run-time N. + */ + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> Last( + index_type aCount) const + { + MOZ_RELEASE_ASSERT(aCount <= size()); + return { data() + (size() - aCount), aCount }; + } + + /** + * Subspan with run-time start index and length. + */ + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> Subspan( + index_type aStart, + index_type aLength = dynamic_extent) const + { + MOZ_RELEASE_ASSERT(aStart <= size() && + (aLength == dynamic_extent || + (aStart + aLength <= size()))); + return { data() + aStart, + aLength == dynamic_extent ? size() - aStart : aLength }; + } + + /** + * Subspan with run-time start index. (Rust's &foo[start..]) + */ + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> From( + index_type aStart) const + { + return Subspan(aStart); + } + + /** + * Subspan with run-time exclusive end index. (Rust's &foo[..end]) + */ + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> To( + index_type aEnd) const + { + return Subspan(0, aEnd); + } + + /** + * Subspan with run-time start index and exclusive end index. + * (Rust's &foo[start..end]) + */ + MOZ_SPAN_GCC_CONSTEXPR Span<element_type, dynamic_extent> FromTo( + index_type aStart, + index_type aEnd) const + { + MOZ_RELEASE_ASSERT(aStart <= aEnd); + return Subspan(aStart, aEnd - aStart); + } + + // [Span.obs], Span observers + /** + * Number of elements in the span. + */ + constexpr index_type Length() const { return size(); } + + /** + * Number of elements in the span (standard-libray duck typing version). + */ + constexpr index_type size() const { return storage_.size(); } + + /** + * Size of the span in bytes. + */ + constexpr index_type LengthBytes() const { return size_bytes(); } + + /** + * Size of the span in bytes (standard-library naming style version). + */ + constexpr index_type size_bytes() const + { + return size() * narrow_cast<index_type>(sizeof(element_type)); + } + + /** + * Checks if the the length of the span is zero. + */ + constexpr bool IsEmpty() const { return empty(); } + + /** + * Checks if the the length of the span is zero (standard-libray duck + * typing version). + */ + constexpr bool empty() const { return size() == 0; } + + // [Span.elem], Span element access + MOZ_SPAN_GCC_CONSTEXPR reference operator[](index_type idx) const + { + MOZ_RELEASE_ASSERT(idx < storage_.size()); + return data()[idx]; + } + + /** + * Access element of span by index (standard-library duck typing version). + */ + constexpr reference at(index_type idx) const { return this->operator[](idx); } + + constexpr reference operator()(index_type idx) const + { + return this->operator[](idx); + } + + /** + * Pointer to the first element of the span. + */ + constexpr pointer Elements() const { return data(); } + + /** + * Pointer to the first element of the span (standard-libray duck typing version). + */ + constexpr pointer data() const { return storage_.data(); } + + // [Span.iter], Span iterator support + iterator begin() const { return { this, 0 }; } + iterator end() const { return { this, Length() }; } + + const_iterator cbegin() const { return { this, 0 }; } + const_iterator cend() const { return { this, Length() }; } + + reverse_iterator rbegin() const + { + return reverse_iterator{ end() }; + } + reverse_iterator rend() const + { + return reverse_iterator{ begin() }; + } + + const_reverse_iterator crbegin() const + { + return const_reverse_iterator{ cend() }; + } + const_reverse_iterator crend() const + { + return const_reverse_iterator{ cbegin() }; + } + +private: + // this implementation detail class lets us take advantage of the + // empty base class optimization to pay for only storage of a single + // pointer in the case of fixed-size Spans + template<class ExtentType> + class storage_type : public ExtentType + { + public: + template<class OtherExtentType> + MOZ_SPAN_ASSERTION_CONSTEXPR storage_type(pointer elements, + OtherExtentType ext) + : ExtentType(ext) + , data_(elements) + { + MOZ_RELEASE_ASSERT( + (!elements && ExtentType::size() == 0) || + (elements && ExtentType::size() != mozilla::MaxValue<size_t>::value)); + } + + constexpr pointer data() const { return data_; } + + private: + pointer data_; + }; + + storage_type<span_details::extent_type<Extent>> storage_; +}; + +// [Span.comparison], Span comparison operators +template<class ElementType, size_t FirstExtent, size_t SecondExtent> +inline constexpr bool +operator==(const Span<ElementType, FirstExtent>& l, + const Span<ElementType, SecondExtent>& r) +{ + return (l.size() == r.size()) && std::equal(l.begin(), l.end(), r.begin()); +} + +template<class ElementType, size_t Extent> +inline constexpr bool +operator!=(const Span<ElementType, Extent>& l, + const Span<ElementType, Extent>& r) +{ + return !(l == r); +} + +template<class ElementType, size_t Extent> +inline constexpr bool +operator<(const Span<ElementType, Extent>& l, + const Span<ElementType, Extent>& r) +{ + return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end()); +} + +template<class ElementType, size_t Extent> +inline constexpr bool +operator<=(const Span<ElementType, Extent>& l, + const Span<ElementType, Extent>& r) +{ + return !(l > r); +} + +template<class ElementType, size_t Extent> +inline constexpr bool +operator>(const Span<ElementType, Extent>& l, + const Span<ElementType, Extent>& r) +{ + return r < l; +} + +template<class ElementType, size_t Extent> +inline constexpr bool +operator>=(const Span<ElementType, Extent>& l, + const Span<ElementType, Extent>& r) +{ + return !(l < r); +} + +namespace span_details { +// if we only supported compilers with good constexpr support then +// this pair of classes could collapse down to a constexpr function + +// we should use a narrow_cast<> to go to size_t, but older compilers may not see it as +// constexpr +// and so will fail compilation of the template +template<class ElementType, size_t Extent> +struct calculate_byte_size + : mozilla::IntegralConstant<size_t, + static_cast<size_t>(sizeof(ElementType) * + static_cast<size_t>(Extent))> +{ +}; + +template<class ElementType> +struct calculate_byte_size<ElementType, dynamic_extent> + : mozilla::IntegralConstant<size_t, dynamic_extent> +{ +}; +} + +// [Span.objectrep], views of object representation +/** + * View span as Span<const uint8_t>. + */ +template<class ElementType, size_t Extent> +Span<const uint8_t, + span_details::calculate_byte_size<ElementType, Extent>::value> +AsBytes(Span<ElementType, Extent> s) +{ + return { reinterpret_cast<const uint8_t*>(s.data()), s.size_bytes() }; +} + +/** + * View span as Span<uint8_t>. + */ +template<class ElementType, + size_t Extent, + class = span_details::enable_if_t<!mozilla::IsConst<ElementType>::value>> +Span<uint8_t, span_details::calculate_byte_size<ElementType, Extent>::value> +AsWritableBytes(Span<ElementType, Extent> s) +{ + return { reinterpret_cast<uint8_t*>(s.data()), s.size_bytes() }; +} + +// +// MakeSpan() - Utility functions for creating Spans +// +/** + * Create span from pointer and length. + */ +template<class ElementType> +Span<ElementType> +MakeSpan(ElementType* aPtr, typename Span<ElementType>::index_type aLength) +{ + return Span<ElementType>(aPtr, aLength); +} + +/** + * Create span from start pointer and pointer past end. + */ +template<class ElementType> +Span<ElementType> +MakeSpan(ElementType* aStartPtr, ElementType* aEndPtr) +{ + return Span<ElementType>(aStartPtr, aEndPtr); +} + +/** + * Create span from C array. + */ +template<class ElementType, size_t N> +Span<ElementType> MakeSpan(ElementType (&aArr)[N]) +{ + return Span<ElementType>(aArr); +} + +/** + * Create span from mozilla::Array. + */ +template<class ElementType, size_t N> +Span<ElementType> +MakeSpan(mozilla::Array<ElementType, N>& aArr) +{ + return aArr; +} + +/** + * Create span from const mozilla::Array. + */ +template<class ElementType, size_t N> +Span<const ElementType> +MakeSpan(const mozilla::Array<ElementType, N>& arr) +{ + return arr; +} + +/** + * Create span from standard-library container. + */ +template<class Container> +Span<typename Container::value_type> +MakeSpan(Container& cont) +{ + return Span<typename Container::value_type>(cont); +} + +/** + * Create span from standard-library container (const version). + */ +template<class Container> +Span<const typename Container::value_type> +MakeSpan(const Container& cont) +{ + return Span<const typename Container::value_type>(cont); +} + +/** + * Create span from smart pointer and length. + */ +template<class Ptr> +Span<typename Ptr::element_type> +MakeSpan(Ptr& aPtr, size_t aLength) +{ + return Span<typename Ptr::element_type>(aPtr, aLength); +} + +/** + * Create span from C string. + */ +inline Span<const char> +MakeCStringSpan(const char* aStr) +{ + return Span<const char>(aStr, std::strlen(aStr)); +} + +} // namespace mozilla + +#ifdef _MSC_VER +#if _MSC_VER < 1910 +#undef constexpr +#pragma pop_macro("constexpr") + +#endif // _MSC_VER < 1910 + +#pragma warning(pop) +#endif // _MSC_VER + +#undef MOZ_SPAN_ASSERTION_CONSTEXPR +#undef MOZ_SPAN_GCC_CONSTEXPR +#undef MOZ_SPAN_EXPLICITLY_DEFAULTED_CONSTEXPR +#undef MOZ_SPAN_CONSTEXPR_NOT_JUST_RETURN +#undef MOZ_SPAN_NON_CONST_CONSTEXPR + +#endif // mozilla_Span_h |