1 /*
2 * Copyright 2018 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #ifndef SkSpan_DEFINED
9 #define SkSpan_DEFINED
10
11 #include <cstddef>
12 #include <iterator>
13 #include <type_traits>
14 #include <utility>
15 #include "include/private/SkTLogic.h"
16
17 /**
18 * An SkSpan is a view of a contiguous collection of elements of type T. It can be directly
19 * constructed from a pointer and size. SkMakeSpan can be used to construct one from an array,
20 * or a container (like std::vector).
21 *
22 * With C++17, we could add template deduction guides that eliminate the need for SkMakeSpan:
23 * https://skia-review.googlesource.com/c/skia/+/320264
24 */
25 template <typename T>
26 class SkSpan {
27 public:
SkSpan()28 constexpr SkSpan() : fPtr{nullptr}, fSize{0} {}
SkSpan(T * ptr,size_t size)29 constexpr SkSpan(T* ptr, size_t size) : fPtr{ptr}, fSize{size} {}
30 template <typename U, typename = typename std::enable_if<std::is_same<const U, T>::value>::type>
SkSpan(const SkSpan<U> & that)31 constexpr SkSpan(const SkSpan<U>& that) : fPtr(that.data()), fSize{that.size()} {}
32 constexpr SkSpan(const SkSpan& o) = default;
33
34 constexpr SkSpan& operator=(const SkSpan& that) {
35 fPtr = that.fPtr;
36 fSize = that.fSize;
37 return *this;
38 }
39 constexpr T& operator [] (size_t i) const {
40 SkASSERT(i < this->size());
41 return fPtr[i];
42 }
front()43 constexpr T& front() const { return fPtr[0]; }
back()44 constexpr T& back() const { return fPtr[fSize - 1]; }
begin()45 constexpr T* begin() const { return fPtr; }
end()46 constexpr T* end() const { return fPtr + fSize; }
rbegin()47 constexpr auto rbegin() const { return std::make_reverse_iterator(this->end()); }
rend()48 constexpr auto rend() const { return std::make_reverse_iterator(this->begin()); }
data()49 constexpr T* data() const { return this->begin(); }
size()50 constexpr size_t size() const { return fSize; }
empty()51 constexpr bool empty() const { return fSize == 0; }
size_bytes()52 constexpr size_t size_bytes() const { return fSize * sizeof(T); }
first(size_t prefixLen)53 constexpr SkSpan<T> first(size_t prefixLen) const {
54 SkASSERT(prefixLen <= this->size());
55 return SkSpan{fPtr, prefixLen};
56 }
last(size_t postfixLen)57 constexpr SkSpan<T> last(size_t postfixLen) const {
58 SkASSERT(postfixLen <= this->size());
59 return SkSpan{fPtr + (this->size() - postfixLen), postfixLen};
60 }
subspan(size_t offset,size_t count)61 constexpr SkSpan<T> subspan(size_t offset, size_t count) const {
62 SkASSERT(offset <= this->size());
63 SkASSERT(count <= this->size() - offset);
64 return SkSpan{fPtr + offset, count};
65 }
66
67 private:
68 T* fPtr;
69 size_t fSize;
70 };
71
SkMakeSpan(T * p,S s)72 template <typename T, typename S> inline constexpr SkSpan<T> SkMakeSpan(T* p, S s) {
73 return SkSpan<T>{p, SkTo<size_t>(s)};
74 }
75
SkMakeSpan(T (& a)[N])76 template <size_t N, typename T> inline constexpr SkSpan<T> SkMakeSpan(T (&a)[N]) {
77 return SkSpan<T>{a, N};
78 }
79
80 template <typename Container>
81 inline auto SkMakeSpan(Container& c)
82 -> SkSpan<typename std::remove_reference<decltype(*(c.data()))>::type> {
83 return {c.data(), c.size()};
84 }
85
86 #endif // SkSpan_DEFINED
87