1/*
2 * Copyright 2019 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 SkZip_DEFINED
9#define SkZip_DEFINED
10
11#include <iterator>
12#include <tuple>
13#include <type_traits>
14#include <utility>
15
16#include "include/core/SkTypes.h"
17#include "include/private/SkTemplates.h"
18#include "include/private/SkTo.h"
19#include "src/core/SkSpan.h"
20
21// Take a list of things that can be pointers, and use them all in parallel. The iterators and
22// accessor operator[] for the class produce a tuple of the items.
23template<typename... Ts>
24class SkZip {
25 using ReturnTuple = std::tuple<Ts&...>;
26
27 class Iterator {
28 public:
29 using value_type = ReturnTuple;
30 using difference_type = ptrdiff_t;
31 using pointer = value_type*;
32 using reference = value_type;
33 using iterator_category = std::input_iterator_tag;
34 constexpr Iterator(const SkZip* zip, size_t index) : fZip{zip}, fIndex{index} { }
35 constexpr Iterator(const Iterator& that) : Iterator{ that.fZip, that.fIndex } { }
36 constexpr Iterator& operator++() { ++fIndex; return *this; }
37 constexpr Iterator operator++(int) { Iterator tmp(*this); operator++(); return tmp; }
38 constexpr bool operator==(const Iterator& rhs) const { return fIndex == rhs.fIndex; }
39 constexpr bool operator!=(const Iterator& rhs) const { return fIndex != rhs.fIndex; }
40 constexpr reference operator*() { return (*fZip)[fIndex]; }
41 friend constexpr difference_type operator-(Iterator lhs, Iterator rhs) {
42 return lhs.fIndex - rhs.fIndex;
43 }
44
45 private:
46 const SkZip* const fZip = nullptr;
47 size_t fIndex = 0;
48 };
49
50 template<typename T>
51 static constexpr T* nullify = nullptr;
52
53public:
54 constexpr SkZip() : fPointers{nullify<Ts>...}, fSize{0} {}
55 constexpr SkZip(size_t) = delete;
56 constexpr SkZip(size_t size, Ts*... ts)
57 : fPointers{ts...}
58 , fSize{size} {}
59 constexpr SkZip(const SkZip& that) = default;
60
61 // Check to see if U can be used for const T or is the same as T
62 template <typename U, typename T>
63 using CanConvertToConst = typename std::integral_constant<bool,
64 std::is_convertible<U*, T*>::value && sizeof(U) == sizeof(T)>::type;
65
66 // Allow SkZip<const T> to be constructed from SkZip<T>.
67 template<typename... Us,
68 typename = std::enable_if<skstd::conjunction<CanConvertToConst<Us, Ts>...>::value>>
69 constexpr SkZip(const SkZip<Us...>& that)
70 : fPointers(that.data())
71 , fSize{that.size()} { }
72
73 constexpr ReturnTuple operator[](size_t i) const { return this->index(i);}
74 constexpr size_t size() const { return fSize; }
75 constexpr bool empty() const { return this->size() == 0; }
76 constexpr ReturnTuple front() const { return this->index(0); }
77 constexpr ReturnTuple back() const { return this->index(this->size() - 1); }
78 constexpr Iterator begin() const { return Iterator{this, 0}; }
79 constexpr Iterator end() const { return Iterator{this, this->size()}; }
80 template<size_t I> constexpr auto get() const {
81 return SkMakeSpan(std::get<I>(fPointers), fSize);
82 }
83 constexpr std::tuple<Ts*...> data() const { return fPointers; }
84 constexpr SkZip first(size_t n) const {
85 SkASSERT(n <= this->size());
86 if (n == 0) { return SkZip(); }
87 return SkZip{n, fPointers};
88 }
89 constexpr SkZip last(size_t n) const {
90 SkASSERT(n <= this->size());
91 if (n == 0) { return SkZip(); }
92 return SkZip{n, this->pointersAt(fSize - n)};
93 }
94 constexpr SkZip subspan(size_t offset, size_t count) const {
95 SkASSERT(offset < this->size());
96 SkASSERT(count <= this->size() - offset);
97 if (count == 0) { return SkZip(); }
98 return SkZip(count, pointersAt(offset));
99 }
100
101private:
102 constexpr SkZip(size_t n, const std::tuple<Ts*...>& pointers)
103 : fPointers{pointers}
104 , fSize{n} {}
105
106 constexpr ReturnTuple index(size_t i) const {
107 SkASSERT(this->size() > 0);
108 SkASSERT(i < this->size());
109 return indexDetail(i, std::make_index_sequence<sizeof...(Ts)>{});
110 }
111
112 template<std::size_t... Is>
113 constexpr ReturnTuple indexDetail(size_t i, std::index_sequence<Is...>) const {
114 return ReturnTuple((std::get<Is>(fPointers))[i]...);
115 }
116
117 std::tuple<Ts*...> pointersAt(size_t i) const {
118 SkASSERT(this->size() > 0);
119 SkASSERT(i < this->size());
120 return pointersAtDetail(i, std::make_index_sequence<sizeof...(Ts)>{});
121 }
122
123 template<std::size_t... Is>
124 constexpr std::tuple<Ts*...> pointersAtDetail(size_t i, std::index_sequence<Is...>) const {
125 return std::tuple<Ts*...>{&(std::get<Is>(fPointers))[i]...};
126 }
127
128 std::tuple<Ts*...> fPointers;
129 size_t fSize;
130};
131
132class SkMakeZipDetail {
133 template<typename T> struct DecayPointer{
134 using U = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
135 using type = typename std::conditional<std::is_pointer<U>::value, U, T>::type;
136 };
137 template<typename T> using DecayPointerT = typename DecayPointer<T>::type;
138
139 template<typename C> struct ContiguousMemory { };
140 template<typename T> struct ContiguousMemory<T*> {
141 using value_type = T;
142 static constexpr value_type* Data(T* t) { return t; }
143 static constexpr size_t Size(T* s) { return SIZE_MAX; }
144 };
145 template<typename T, size_t N> struct ContiguousMemory<T(&)[N]> {
146 using value_type = T;
147 static constexpr value_type* Data(T(&t)[N]) { return t; }
148 static constexpr size_t Size(T(&)[N]) { return N; }
149 };
150 // In general, we don't want r-value collections, but SkSpans are ok, because they are a view
151 // onto an actual container.
152 template<typename T> struct ContiguousMemory<SkSpan<T>> {
153 using value_type = T;
154 static constexpr value_type* Data(SkSpan<T> s) { return s.data(); }
155 static constexpr size_t Size(SkSpan<T> s) { return s.size(); }
156 };
157 // Only accept l-value references to collections.
158 template<typename C> struct ContiguousMemory<C&> {
159 using value_type = typename std::remove_pointer<decltype(std::declval<C>().data())>::type;
160 static constexpr value_type* Data(C& c) { return c.data(); }
161 static constexpr size_t Size(C& c) { return c.size(); }
162 };
163 template<typename C> using Span = ContiguousMemory<DecayPointerT<C>>;
164 template<typename C> using ValueType = typename Span<C>::value_type;
165
166 template<typename C, typename... Ts> struct PickOneSize { };
167 template <typename T, typename... Ts> struct PickOneSize<T*, Ts...> {
168 static constexpr size_t Size(T* t, Ts... ts) {
169 return PickOneSize<Ts...>::Size(std::forward<Ts>(ts)...);
170 }
171 };
172 template <typename T, typename... Ts, size_t N> struct PickOneSize<T(&)[N], Ts...> {
173 static constexpr size_t Size(T(&)[N], Ts...) { return N; }
174 };
175 template<typename T, typename... Ts> struct PickOneSize<SkSpan<T>, Ts...> {
176 static constexpr size_t Size(SkSpan<T> s, Ts...) { return s.size(); }
177 };
178 template<typename C, typename... Ts> struct PickOneSize<C&, Ts...> {
179 static constexpr size_t Size(C& c, Ts...) { return c.size(); }
180 };
181
182public:
183 template<typename... Ts>
184 static constexpr auto MakeZip(Ts&& ... ts) {
185
186 // Pick the first collection that has a size, and use that for the size.
187 size_t size = PickOneSize<DecayPointerT<Ts>...>::Size(std::forward<Ts>(ts)...);
188
189#ifdef SK_DEBUG
190 // Check that all sizes are the same.
191 size_t minSize = SIZE_MAX;
192 size_t maxSize = 0;
193 for (size_t s : {Span<Ts>::Size(std::forward<Ts>(ts))...}) {
194 if (s != SIZE_MAX) {
195 minSize = std::min(minSize, s);
196 maxSize = std::max(maxSize, s);
197 }
198 }
199 SkASSERT(minSize == maxSize);
200#endif
201
202 return SkZip<ValueType<Ts>...>{size, Span<Ts>::Data(std::forward<Ts>(ts))...};
203 }
204};
205
206template<typename... Ts>
207template<typename T>
208constexpr T* SkZip<Ts...>::nullify;
209
210template<typename... Ts>
211inline constexpr auto SkMakeZip(Ts&& ... ts) {
212 return SkMakeZipDetail::MakeZip(std::forward<Ts>(ts)...);
213}
214#endif //SkZip_DEFINED
215