// ********************************************************* -*- C++ -*-
/*
* Copyright (C) 2004-2018 Exiv2 maintainers
*
* This program is part of the Exiv2 distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, 5th Floor, Boston, MA 02110-1301 USA.
*/
/*!
@file slice.hpp
@brief Simple implementation of slices (=views) for STL containers and C-arrays
@author Dan Čermák (D4N)
<a href="mailto:dan.cermak@cgc-instruments.com">dan.cermak@cgc-instruments.com</a>
@date 30-March-18, D4N: created
*/
#ifndef EXIV2_INCLUDE_SLICE_HPP
#define EXIV2_INCLUDE_SLICE_HPP
#include <cassert>
#include <cstddef>
#include <iterator>
#include <stdexcept>
namespace Exiv2
{
namespace Internal
{
// TODO: remove these custom implementations once we have C++11
template <class T>
struct remove_const
{
typedef T type;
};
template <class T>
struct remove_const<const T>
{
typedef T type;
};
template <class T>
struct remove_volatile
{
typedef T type;
};
template <class T>
struct remove_volatile<volatile T>
{
typedef T type;
};
template <class T>
struct remove_cv
{
typedef typename remove_const<typename remove_volatile<T>::type>::type type;
};
template <class T>
struct remove_pointer
{
typedef T type;
};
template <class T>
struct remove_pointer<T*>
{
typedef T type;
};
template <class T>
struct remove_pointer<T* const>
{
typedef T type;
};
/*!
* Common base class of all slice implementations.
*
* Implements only the most basic functions, which do not require any
* knowledge about the stored data.
*/
struct SliceBase
{
inline SliceBase(size_t begin, size_t end) : begin_(begin), end_(end)
{
if (begin >= end) {
throw std::out_of_range("Begin must be smaller than end");
}
}
/*!
* Return the number of elements in the slice.
*/
inline size_t size() const throw()
{
// cannot underflow, as we know that begin < end
return end_ - begin_;
}
protected:
/*!
* Throw an exception when index is too large.
*
* @throw std::out_of_range when `index` will access an element
* outside of the slice
*/
inline void rangeCheck(size_t index) const
{
if (index >= size()) {
throw std::out_of_range("Index outside of the slice");
}
}
/*!
* lower and upper bounds of the slice with respect to the
* container/array stored in storage_
*/
const size_t begin_, end_;
};
/*!
* @brief This class provides the public-facing const-qualified methods
* of a slice.
*
* The public methods are implemented in a generic fashion using a
* storage_type. This type contains the actual reference to the data to
* which the slice points and provides the following methods:
*
* - (const) value_type& unsafeAt(size_t index) (const)
* Return the value at the given index of the underlying container,
* without promising to perform a range check and without any
* knowledge of the slices' size
*
* - const_iterator/iterator unsafeGetIteratorAt(size_t index) (const)
* Return a (constant) iterator at the given index of the underlying
* container. Again, no range checks are promised.
*
* - Constructor(data_type& data, size_t begin, size_t end)
* Can use `begin` & `end` to perform range checks on `data`, but
* should not store both values. Must not take ownership of `data`!
*
* - Must save data as a public member named `data_`.
*
* - Must provide appropriate typedefs for iterator, const_iterator and
* value_type
*/
template <template <typename data_type> class storage_type, typename data_type>
struct ConstSliceBase : SliceBase
{
typedef typename storage_type<data_type>::iterator iterator;
typedef typename storage_type<data_type>::const_iterator const_iterator;
typedef typename storage_type<data_type>::value_type value_type;
/*!
* Default contructor, requires begin to be smaller than end,
* otherwise an exception is thrown. Also forwards all parameters to
* the constructor of storage_
*/
ConstSliceBase(data_type& data, size_t begin, size_t end)
: SliceBase(begin, end), storage_(data, begin, end)
{
}
/*!
* Obtain a constant reference to the element with the specified
* index in the slice.
*
* @throw std::out_of_range when index is out of bounds of the slice
*/
const value_type& at(size_t index) const
{
rangeCheck(index);
// we know: begin_ < end <= size() <= SIZE_T_MAX
// and: index < end - begin
// thus: index + begin < end <= SIZE_T_MAX
// => no overflow is possible
return storage_.unsafeAt(begin_ + index);
}
/*!
* Obtain a constant iterator to the first element in the slice.
*/
const_iterator cbegin() const throw()
{
return storage_.unsafeGetIteratorAt(begin_);
}
/*!
* Obtain a constant iterator to the first beyond the slice.
*/
const_iterator cend() const throw()
{
return storage_.unsafeGetIteratorAt(end_);
}
/*!
* Create a constant sub-slice with the given bounds (with respect
* to the current slice).
*
* @tparam slice_type Type of the slice that this function shall
* return. Provide it with the type of the class that derives from
* mutable_slice_base.
*/
template <typename slice_type>
slice_type subSlice(size_t begin, size_t end) const
{
this->rangeCheck(begin);
// end == size() is a legal value, since end is the first
// element beyond the slice
// end == 0 is not a legal value (subtraction will underflow and
// throw an exception)
this->rangeCheck(end - 1);
// additions are safe, begin and end are smaller than size()
const size_t new_begin = begin + this->begin_;
const size_t new_end = this->begin_ + end;
if (new_end > this->end_) {
throw std::out_of_range("Invalid input parameters to slice");
}
return slice_type(storage_.data_, new_begin, new_end);
}
protected:
/*!
* Stores a reference to the actual data.
*/
storage_type<data_type> storage_;
};
/*!
* This class provides all public-facing non-const-qualified methods of
* slices. It only re-implements the const-qualified versions as
* non-const.
*/
template <template <typename> class storage_type, typename data_type>
struct MutableSliceBase : public ConstSliceBase<storage_type, data_type>
{
typedef typename ConstSliceBase<storage_type, data_type>::iterator iterator;
typedef typename ConstSliceBase<storage_type, data_type>::const_iterator const_iterator;
typedef typename ConstSliceBase<storage_type, data_type>::value_type value_type;
/*!
* Forwards everything to the constructor of const_slice_base
*
* @todo use using once we have C++11
*/
MutableSliceBase(data_type& data, size_t begin, size_t end)
: ConstSliceBase<storage_type, data_type>(data, begin, end)
{
}
/*!
* Obtain a reference to the element with the specified index in the
* slice.
*
* @throw std::out_of_range when index is out of bounds of the slice
*/
value_type& at(size_t index)
{
this->rangeCheck(index);
return this->storage_.unsafeAt(this->begin_ + index);
}
const value_type& at(size_t index) const
{
// TODO: use using base_type::at once we have C++11
return base_type::at(index);
}
/*!
* Obtain an iterator to the first element in the slice.
*/
iterator begin() throw()
{
return this->storage_.unsafeGetIteratorAt(this->begin_);
}
/*!
* Obtain an iterator to the first element beyond the slice.
*/
iterator end() throw()
{
return this->storage_.unsafeGetIteratorAt(this->end_);
}
protected:
/*!
* Explicitly convert this instance into a base-class of the
* appropriate constant version of this slice.
*
* This function is required to properly implement the `subSlice()
* const` function for mutable slices. The problem here is, that a
* slice<T> and a slice<const T> actually don't share the same base
* class `ConstSliceBase<storage_type, T>`. Instead `slice<T>`
* inherits from `ConstSliceBase<storage_type, T>` and `slice<const
* T>` inherits from `ConstSliceBase<storage_type, const T>`.
*
* Now, `slice<T>` can call the `subSlice() const` method from its
* base class, but that will return a mutable `slice<T>`! Instead we
* use this function to convert the ``slice<T>` into the parent of
* the appropriate `slice<const T>` and call its `subSlice() const`,
* which returns the correct type.
*/
ConstSliceBase<storage_type, const data_type> to_const_base() const throw()
{
return ConstSliceBase<storage_type, const data_type>(this->storage_.data_, this->begin_, this->end_);
}
typedef ConstSliceBase<storage_type, data_type> base_type;
/*!
* Create a mutable sub-slice with the given bounds (with respect to
* the current slice).
*
* @tparam slice_type Type of the slice that this function shall
* return. Provide it with the type of the class that derives from
* mutable_slice_base.
*/
template <typename slice_type>
slice_type subSlice(size_t begin, size_t end)
{
this->rangeCheck(begin);
// end == size() is a legal value, since end is the first
// element beyond the slice
// end == 0 is not a legal value (subtraction will underflow and
// throw an exception)
this->rangeCheck(end - 1);
// additions are safe, begin & end are smaller than size()
const size_t new_begin = begin + this->begin_;
const size_t new_end = this->begin_ + end;
if (new_end > this->end_) {
throw std::out_of_range("Invalid input parameters to slice");
}
return slice_type(this->storage_.data_, new_begin, new_end);
}
};
/*!
* Implementation of the storage concept for STL-containers.
*
* @tparam container Type of the STL-container.
*/
template <typename container>
struct ContainerStorage
{
typedef typename container::iterator iterator;
typedef typename container::const_iterator const_iterator;
typedef typename Internal::remove_cv<typename container::value_type>::type value_type;
/*!
* @throw std::out_of_range when end is larger than the container's
* size.
*/
ContainerStorage(container& data, size_t /* begin*/, size_t end) : data_(data)
{
if (end > data.size()) {
throw std::out_of_range("Invalid input parameters to slice");
}
}
/*!
* Obtain a constant reference to the element with the given `index`
* in the container.
*
* @throw whatever container::at() throws
*/
const value_type& unsafeAt(size_t index) const
{
return data_.at(index);
}
value_type& unsafeAt(size_t index)
{
return data_.at(index);
}
/*!
* Obtain an iterator at the position of the element with the given
* index in the container.
*
* @throw whatever container::begin() and std::advance() throw
*/
iterator unsafeGetIteratorAt(size_t index)
{
// we are screwed if the container got changed => try to catch it
assert(index <= data_.size());
iterator it = data_.begin();
std::advance(it, index);
return it;
}
const_iterator unsafeGetIteratorAt(size_t index) const
{
assert(index <= data_.size());
const_iterator it = data_.begin();
std::advance(it, index);
return it;
}
container& data_;
};
/*!
* @brief Implementation of the storage concept for slices of C arrays.
*
* @tparam storage_type Type as which the C-array should be stored. Use
* this parameter to save constant arrays as `const` and mutable ones as
* non-`const`.
*/
template <typename storage_type>
struct PtrSliceStorage
{
typedef typename remove_cv<typename remove_pointer<storage_type>::type>::type value_type;
typedef value_type* iterator;
typedef const value_type* const_iterator;
/*!
* Stores ptr and checks that it is not `NULL`. The slice's bounds
* are ignored, as we do not know the array's length.
*
* @throw std::invalid_argument when ptr is `NULL`
*/
PtrSliceStorage(storage_type ptr, size_t /*begin*/, size_t /*end*/) : data_(ptr)
{
// TODO: change this to nullptr once we use C++11
if (ptr == NULL) {
throw std::invalid_argument("Null pointer passed to slice constructor");
}
}
/*!
* Obtain a reference to the element with the given `index` in the
* array.
*
* @throw nothing
*/
value_type& unsafeAt(size_t index) throw()
{
return data_[index];
}
const value_type& unsafeAt(size_t index) const throw()
{
return data_[index];
}
/*!
* Obtain an iterator (=pointer) at the position of the element with
* the given index in the container.
*
* @throw nothing
*/
iterator unsafeGetIteratorAt(size_t index) throw()
{
return data_ + index;
}
const_iterator unsafeGetIteratorAt(size_t index) const throw()
{
return data_ + index;
}
storage_type data_;
};
} // namespace Internal
/*!
* @brief Slice (= view) for STL containers.
*
* This is a very simple implementation of slices (i.e. views of sub-arrays)
* for STL containers that support O(1) element access and random access
* iterators (like std::vector, std::array and std::string).
*
* A slice represents the semi-open interval [begin, end) and provides a
* (mutable) view, it does however not own the data! It can be used to
* conveniently pass parts of containers into functions without having to use
* iterators or offsets.
*
* In contrast to C++20's std::span<T> it is impossible to read beyond the
* container's bounds and unchecked access is not-possible (by design).
*
* Example usage:
* ~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
* std::vector<int> vec = {0, 1, 2, 3, 4};
* slice<std::vector<int> > one_two(vec, 1, 3);
* assert(one_two.size() == 2);
* assert(one_two.at(0) == 1 && one_two.at(1) == 2);
* // mutate the contents:
* one_two.at(0) *= 2;
* one_two.at(1) *= 3;
* assert(one_two.at(0) == 2 && one_two.at(1) == 6);
* ~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Slices also offer access via iterators of the same type as the underlying
* container, so that they can be used in a comparable fashion:
* ~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
* std::vector<int> vec = {0, 1, 2, 3, 4};
* slice<std::vector<int>> three_four(vec, 3, 5);
* assert(*three_four.begin() == 3 && *three_four.end() == 4);
* // this prints:
* // 3
* // 4
* for (const auto & elem : three_four) {
* std::cout << elem << std::endl;
* }
* ~~~~~~~~~~~~~~~~~~~~~~~~~
*
* @tparam container A STL container type, like vector or array. Must support
* array-like access via the `at()` method.
*/
template <typename container>
struct Slice : public Internal::MutableSliceBase<Internal::ContainerStorage, container>
{
typedef typename container::iterator iterator;
typedef typename container::const_iterator const_iterator;
typedef typename Internal::remove_cv<typename container::value_type>::type value_type;
/*!
* @brief Construct a slice of the container `cont` starting at `begin`
* (including) and ending before `end`.
*
* @param[in] cont Reference to the container
* @param[in] begin First element of the slice.
* @param[in] end First element beyond the slice.
*
* @throws std::out_of_range For invalid slice bounds: when end is not
* larger than begin or when the slice's bounds are larger than the
* container's size.
*
* Please note that due to the requirement that `end` must be larger
* than `begin` (they cannot be equal) it is impossible to construct a
* slice with zero length.
*/
Slice(container& cont, size_t begin, size_t end)
: Internal::MutableSliceBase<Internal::ContainerStorage, container>(cont, begin, end)
{
}
/*!
* Construct a sub-slice of this slice with the given bounds. The bounds
* are evaluated with respect to the current slice.
*
* @param[in] begin First element in the new slice.
* @param[in] end First element beyond the new slice.
*
* @throw std::out_of_range when begin or end are invalid
*/
Slice subSlice(size_t begin, size_t end)
{
return Internal::MutableSliceBase<Internal::ContainerStorage, container>::template subSlice<Slice>(begin,
end);
}
/*!
* Constructs a new constant subSlice. Behaves otherwise exactly like
* the non-const version.
*/
Slice<const container> subSlice(size_t begin, size_t end) const
{
return this->to_const_base().template subSlice<Slice<const container> >(begin, end);
}
};
/*!
* @brief Specialization of slices for constant containers.
*/
template <typename container>
struct Slice<const container> : public Internal::ConstSliceBase<Internal::ContainerStorage, const container>
{
typedef typename container::iterator iterator;
typedef typename container::const_iterator const_iterator;
typedef typename Internal::remove_cv<typename container::value_type>::type value_type;
Slice(const container& cont, size_t begin, size_t end)
: Internal::ConstSliceBase<Internal::ContainerStorage, const container>(cont, begin, end)
{
}
Slice subSlice(size_t begin, size_t end) const
{
return Internal::ConstSliceBase<Internal::ContainerStorage,
const container>::template subSlice<Slice<const container> >(begin, end);
}
};
/*!
* Specialization of slices for constant C-arrays.
*
* These have exactly the same interface as the slices for STL-containers,
* with the *crucial* exception, that the slice's constructor *cannot* make
* a proper bounds check! It can only verify that you didn't accidentally
* swap begin and end!
*/
template <typename T>
struct Slice<const T*> : public Internal::ConstSliceBase<Internal::PtrSliceStorage, const T*>
{
/*!
* Constructor.
*
* @param[in] ptr C-array of which a slice should be constructed. Must
* not be a null pointer.
* @param[in] begin Index of the first element in the slice.
* @param[in] end Index of the first element that is no longer in the
* slice.
*
* Please note that the constructor has no way how to verify that
* `begin` and `end` are not out of bounds of the provided array!
*/
Slice(const T* ptr, size_t begin, size_t end)
: Internal::ConstSliceBase<Internal::PtrSliceStorage, const T*>(ptr, begin, end)
{
// TODO: use using in C++11
}
Slice<const T*> subSlice(size_t begin, size_t end) const
{
return Internal::ConstSliceBase<Internal::PtrSliceStorage, const T*>::template subSlice<Slice<const T*> >(
begin, end);
}
};
/*!
* Specialization of slices for (mutable) C-arrays.
*/
template <typename T>
struct Slice<T*> : public Internal::MutableSliceBase<Internal::PtrSliceStorage, T*>
{
Slice(T* ptr, size_t begin, size_t end)
: Internal::MutableSliceBase<Internal::PtrSliceStorage, T*>(ptr, begin, end)
{
// TODO: use using in C++11
}
Slice<T*> subSlice(size_t begin, size_t end)
{
return Internal::MutableSliceBase<Internal::PtrSliceStorage, T*>::template subSlice<Slice<T*> >(begin, end);
}
Slice<const T*> subSlice(size_t begin, size_t end) const
{
return this->to_const_base().template subSlice<Slice<const T*> >(begin, end);
}
};
/*!
* @brief Return a new slice with the given bounds.
*
* Convenience wrapper around the slice's constructor for automatic template
* parameter deduction.
*/
template <typename T>
inline Slice<T> makeSlice(T& cont, size_t begin, size_t end)
{
return Slice<T>(cont, begin, end);
}
/*!
* Overload of makeSlice for slices of C-arrays.
*/
template <typename T>
inline Slice<T*> makeSlice(T* ptr, size_t begin, size_t end)
{
return Slice<T*>(ptr, begin, end);
}
/*!
* @brief Return a new slice spanning the whole container.
*/
template <typename container>
inline Slice<container> makeSlice(container& cont)
{
return Slice<container>(cont, 0, cont.size());
}
/*!
* @brief Return a new slice spanning from begin until the end of the
* container.
*/
template <typename container>
inline Slice<container> makeSliceFrom(container& cont, size_t begin)
{
return Slice<container>(cont, begin, cont.size());
}
/*!
* @brief Return a new slice spanning until `end`.
*/
template <typename container>
inline Slice<container> makeSliceUntil(container& cont, size_t end)
{
return Slice<container>(cont, 0, end);
}
/*!
* Overload of makeSliceUntil for pointer based slices.
*/
template <typename T>
inline Slice<T*> makeSliceUntil(T* ptr, size_t end)
{
return Slice<T*>(ptr, 0, end);
}
} // namespace Exiv2
#endif /* EXIV2_INCLUDE_SLICE_HPP */