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 SkASSERT(size < kMaxSize);
31 }
32 template <typename U, typename = typename std::enable_if<std::is_same<const U, T>::value>::type>
SkSpan(const SkSpan<U> & that)33 constexpr SkSpan(const SkSpan<U>& that) : fPtr(that.data()), fSize{that.size()} {}
34 constexpr SkSpan(const SkSpan& o) = default;
35
36 constexpr SkSpan& operator=(const SkSpan& that) {
37 fPtr = that.fPtr;
38 fSize = that.fSize;
39 return *this;
40 }
41 constexpr T& operator [] (size_t i) const {
42 SkASSERT(i < this->size());
43 return fPtr[i];
44 }
front()45 constexpr T& front() const { return fPtr[0]; }
back()46 constexpr T& back() const { return fPtr[fSize - 1]; }
begin()47 constexpr T* begin() const { return fPtr; }
end()48 constexpr T* end() const { return fPtr + fSize; }
rbegin()49 constexpr auto rbegin() const { return std::make_reverse_iterator(this->end()); }
rend()50 constexpr auto rend() const { return std::make_reverse_iterator(this->begin()); }
data()51 constexpr T* data() const { return this->begin(); }
size()52 constexpr size_t size() const { return fSize; }
empty()53 constexpr bool empty() const { return fSize == 0; }
size_bytes()54 constexpr size_t size_bytes() const { return fSize * sizeof(T); }
first(size_t prefixLen)55 constexpr SkSpan<T> first(size_t prefixLen) const {
56 SkASSERT(prefixLen <= this->size());
57 return SkSpan{fPtr, prefixLen};
58 }
last(size_t postfixLen)59 constexpr SkSpan<T> last(size_t postfixLen) const {
60 SkASSERT(postfixLen <= this->size());
61 return SkSpan{fPtr + (this->size() - postfixLen), postfixLen};
62 }
subspan(size_t offset,size_t count)63 constexpr SkSpan<T> subspan(size_t offset, size_t count) const {
64 SkASSERT(offset <= this->size());
65 SkASSERT(count <= this->size() - offset);
66 return SkSpan{fPtr + offset, count};
67 }
68
69 private:
70 static constexpr size_t kMaxSize = std::numeric_limits<size_t>::max() / sizeof(T);
71 T* fPtr;
72 size_t fSize;
73 };
74
SkMakeSpan(T * p,S s)75 template <typename T, typename S> inline constexpr SkSpan<T> SkMakeSpan(T* p, S s) {
76 return SkSpan<T>{p, SkTo<size_t>(s)};
77 }
78
SkMakeSpan(T (& a)[N])79 template <size_t N, typename T> inline constexpr SkSpan<T> SkMakeSpan(T (&a)[N]) {
80 return SkSpan<T>{a, N};
81 }
82
83 template <typename Container>
84 inline auto SkMakeSpan(Container& c)
85 -> SkSpan<typename std::remove_reference<decltype(*(c.data()))>::type> {
86 return {c.data(), c.size()};
87 }
88
89 #endif // SkSpan_DEFINED
90