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/*
* Copyright 2019 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkZip_DEFINED
#define SkZip_DEFINED
#include "include/private/base/SkAssert.h"
#include "include/private/base/SkDebug.h"
#include "include/private/base/SkSpan_impl.h"
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <tuple>
#include <utility>
// Take a list of things that can be pointers, and use them all in parallel. The iterators and
// accessor operator[] for the class produce a tuple of the items.
template<typename... Ts>
class SkZip {
using ReturnTuple = std::tuple<Ts&...>;
class Iterator {
public:
using value_type = ReturnTuple;
using difference_type = ptrdiff_t;
using pointer = value_type*;
using reference = value_type;
using iterator_category = std::input_iterator_tag;
constexpr Iterator(const SkZip* zip, size_t index) : fZip{zip}, fIndex{index} { }
constexpr Iterator(const Iterator& that) : Iterator{ that.fZip, that.fIndex } { }
constexpr Iterator& operator++() { ++fIndex; return *this; }
constexpr Iterator operator++(int) { Iterator tmp(*this); operator++(); return tmp; }
constexpr bool operator==(const Iterator& rhs) const { return fIndex == rhs.fIndex; }
constexpr bool operator!=(const Iterator& rhs) const { return fIndex != rhs.fIndex; }
constexpr reference operator*() { return (*fZip)[fIndex]; }
friend constexpr difference_type operator-(Iterator lhs, Iterator rhs) {
return lhs.fIndex - rhs.fIndex;
}
private:
const SkZip* const fZip = nullptr;
size_t fIndex = 0;
};
template<typename T>
inline static constexpr T* nullify = nullptr;
public:
constexpr SkZip() : fPointers{nullify<Ts>...}, fSize{0} {}
constexpr SkZip(size_t) = delete;
constexpr SkZip(size_t size, Ts*... ts)
: fPointers{ts...}
, fSize{size} {}
constexpr SkZip(const SkZip& that) = default;
constexpr SkZip& operator=(const SkZip &that) = default;
// Check to see if U can be used for const T or is the same as T
template <typename U, typename T>
using CanConvertToConst = typename std::integral_constant<bool,
std::is_convertible<U*, T*>::value && sizeof(U) == sizeof(T)>::type;
// Allow SkZip<const T> to be constructed from SkZip<T>.
template<typename... Us,
typename = std::enable_if<std::conjunction<CanConvertToConst<Us, Ts>...>::value>>
constexpr SkZip(const SkZip<Us...>& that)
: fPointers(that.data())
, fSize{that.size()} { }
constexpr ReturnTuple operator[](size_t i) const { return this->index(i);}
constexpr size_t size() const { return fSize; }
constexpr bool empty() const { return this->size() == 0; }
constexpr ReturnTuple front() const { return this->index(0); }
constexpr ReturnTuple back() const { return this->index(this->size() - 1); }
constexpr Iterator begin() const { return Iterator{this, 0}; }
constexpr Iterator end() const { return Iterator{this, this->size()}; }
template<size_t I> constexpr auto get() const {
return SkSpan(std::get<I>(fPointers), fSize);
}
constexpr std::tuple<Ts*...> data() const { return fPointers; }
constexpr SkZip first(size_t n) const {
SkASSERT(n <= this->size());
if (n == 0) { return SkZip(); }
return SkZip{n, fPointers};
}
constexpr SkZip last(size_t n) const {
SkASSERT(n <= this->size());
if (n == 0) { return SkZip(); }
return SkZip{n, this->pointersAt(fSize - n)};
}
constexpr SkZip subspan(size_t offset, size_t count) const {
SkASSERT(offset < this->size());
SkASSERT(count <= this->size() - offset);
if (count == 0) { return SkZip(); }
return SkZip(count, pointersAt(offset));
}
private:
constexpr SkZip(size_t n, const std::tuple<Ts*...>& pointers)
: fPointers{pointers}
, fSize{n} {}
constexpr ReturnTuple index(size_t i) const {
SkASSERT(this->size() > 0);
SkASSERT(i < this->size());
return indexDetail(i, std::make_index_sequence<sizeof...(Ts)>{});
}
template<std::size_t... Is>
constexpr ReturnTuple indexDetail(size_t i, std::index_sequence<Is...>) const {
return ReturnTuple((std::get<Is>(fPointers))[i]...);
}
std::tuple<Ts*...> pointersAt(size_t i) const {
SkASSERT(this->size() > 0);
SkASSERT(i < this->size());
return pointersAtDetail(i, std::make_index_sequence<sizeof...(Ts)>{});
}
template<std::size_t... Is>
constexpr std::tuple<Ts*...> pointersAtDetail(size_t i, std::index_sequence<Is...>) const {
return std::tuple<Ts*...>{&(std::get<Is>(fPointers))[i]...};
}
std::tuple<Ts*...> fPointers;
size_t fSize;
};
class SkMakeZipDetail {
template<typename T> struct DecayPointer{
using U = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
using type = typename std::conditional<std::is_pointer<U>::value, U, T>::type;
};
template<typename T> using DecayPointerT = typename DecayPointer<T>::type;
template<typename C> struct ContiguousMemory { };
template<typename T> struct ContiguousMemory<T*> {
using value_type = T;
static constexpr value_type* Data(T* t) { return t; }
static constexpr size_t Size(T* s) { return SIZE_MAX; }
};
template<typename T, size_t N> struct ContiguousMemory<T(&)[N]> {
using value_type = T;
static constexpr value_type* Data(T(&t)[N]) { return t; }
static constexpr size_t Size(T(&)[N]) { return N; }
};
// In general, we don't want r-value collections, but SkSpans are ok, because they are a view
// onto an actual container.
template<typename T> struct ContiguousMemory<SkSpan<T>> {
using value_type = T;
static constexpr value_type* Data(SkSpan<T> s) { return s.data(); }
static constexpr size_t Size(SkSpan<T> s) { return s.size(); }
};
// Only accept l-value references to collections.
template<typename C> struct ContiguousMemory<C&> {
using value_type = typename std::remove_pointer<decltype(std::declval<C>().data())>::type;
static constexpr value_type* Data(C& c) { return c.data(); }
static constexpr size_t Size(C& c) { return c.size(); }
};
template<typename C> using Span = ContiguousMemory<DecayPointerT<C>>;
template<typename C> using ValueType = typename Span<C>::value_type;
template<typename C, typename... Ts> struct PickOneSize { };
template <typename T, typename... Ts> struct PickOneSize<T*, Ts...> {
static constexpr size_t Size(T* t, Ts... ts) {
return PickOneSize<Ts...>::Size(std::forward<Ts>(ts)...);
}
};
template <typename T, typename... Ts, size_t N> struct PickOneSize<T(&)[N], Ts...> {
static constexpr size_t Size(T(&)[N], Ts...) { return N; }
};
template<typename T, typename... Ts> struct PickOneSize<SkSpan<T>, Ts...> {
static constexpr size_t Size(SkSpan<T> s, Ts...) { return s.size(); }
};
template<typename C, typename... Ts> struct PickOneSize<C&, Ts...> {
static constexpr size_t Size(C& c, Ts...) { return c.size(); }
};
public:
template<typename... Ts>
static constexpr auto MakeZip(Ts&& ... ts) {
// Pick the first collection that has a size, and use that for the size.
size_t size = PickOneSize<DecayPointerT<Ts>...>::Size(std::forward<Ts>(ts)...);
#ifdef SK_DEBUG
// Check that all sizes are the same.
size_t minSize = SIZE_MAX;
size_t maxSize = 0;
for (size_t s : {Span<Ts>::Size(std::forward<Ts>(ts))...}) {
if (s != SIZE_MAX) {
minSize = std::min(minSize, s);
maxSize = std::max(maxSize, s);
}
}
SkASSERT(minSize == maxSize);
#endif
return SkZip<ValueType<Ts>...>{size, Span<Ts>::Data(std::forward<Ts>(ts))...};
}
};
template<typename... Ts>
SkZip(size_t size, Ts*... ts) -> SkZip<Ts...>;
template<typename... Ts>
inline constexpr auto SkMakeZip(Ts&& ... ts) {
return SkMakeZipDetail::MakeZip(std::forward<Ts>(ts)...);
}
#endif //SkZip_DEFINED
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