xref: /third_party/skia/include/core/SkSpan.h (revision cb93a386) 
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 */
25template <typename T>
26class SkSpan {
27public:
28    constexpr SkSpan() : fPtr{nullptr}, fSize{0} {}
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>
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    }
45    constexpr T& front() const { return fPtr[0]; }
46    constexpr T& back()  const { return fPtr[fSize - 1]; }
47    constexpr T* begin() const { return fPtr; }
48    constexpr T* end() const { return fPtr + fSize; }
49    constexpr auto rbegin() const { return std::make_reverse_iterator(this->end()); }
50    constexpr auto rend() const { return std::make_reverse_iterator(this->begin()); }
51    constexpr T* data() const { return this->begin(); }
52    constexpr size_t size() const { return fSize; }
53    constexpr bool empty() const { return fSize == 0; }
54    constexpr size_t size_bytes() const { return fSize * sizeof(T); }
55    constexpr SkSpan<T> first(size_t prefixLen) const {
56        SkASSERT(prefixLen <= this->size());
57        return SkSpan{fPtr, prefixLen};
58    }
59    constexpr SkSpan<T> last(size_t postfixLen) const {
60        SkASSERT(postfixLen <= this->size());
61        return SkSpan{fPtr + (this->size() - postfixLen), postfixLen};
62    }
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
69private:
70    static constexpr size_t kMaxSize = std::numeric_limits<size_t>::max() / sizeof(T);
71    T* fPtr;
72    size_t fSize;
73};
74
75template <typename T, typename S> inline constexpr SkSpan<T> SkMakeSpan(T* p, S s) {
76    return SkSpan<T>{p, SkTo<size_t>(s)};
77}
78
79template <size_t N, typename T> inline constexpr SkSpan<T> SkMakeSpan(T (&a)[N]) {
80    return SkSpan<T>{a, N};
81}
82
83template <typename Container>
84inline 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