buffer_info.h

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/*
    pybind11/buffer_info.h: Python buffer object interface
 
    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
 
    All rights reserved. Use of this source code is governed by a
    BSD-style license that can be found in the LICENSE file.
*/
 
#pragma once
 
#include "detail/common.h"
 
PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
PYBIND11_NAMESPACE_BEGIN(detail)
 
// Default, C-style strides
inline std::vector<ssize_t> c_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
    auto ndim = shape.size();
    std::vector<ssize_t> strides(ndim, itemsize);
    if (ndim > 0) {
        for (size_t i = ndim - 1; i > 0; --i) {
            strides[i - 1] = strides[i] * shape[i];
        }
    }
    return strides;
}
 
// F-style strides; default when constructing an array_t with `ExtraFlags & f_style`
inline std::vector<ssize_t> f_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
    auto ndim = shape.size();
    std::vector<ssize_t> strides(ndim, itemsize);
    for (size_t i = 1; i < ndim; ++i) {
        strides[i] = strides[i - 1] * shape[i - 1];
    }
    return strides;
}
 
template <typename T, typename SFINAE = void>
struct compare_buffer_info;
 
PYBIND11_NAMESPACE_END(detail)
 
struct buffer_info {
    void *ptr = nullptr;          // Pointer to the underlying storage
    ssize_t itemsize = 0;         // Size of individual items in bytes
    ssize_t size = 0;             // Total number of entries
    std::string format;           // For homogeneous buffers, this should be set to
                                  // format_descriptor<T>::format()
    ssize_t ndim = 0;             // Number of dimensions
    std::vector<ssize_t> shape;   // Shape of the tensor (1 entry per dimension)
    std::vector<ssize_t> strides; // Number of bytes between adjacent entries
                                  // (for each per dimension)
    bool readonly = false;        // flag to indicate if the underlying storage may be written to
 
    buffer_info() = default;
 
    buffer_info(void *ptr,
                ssize_t itemsize,
                const std::string &format,
                ssize_t ndim,
                detail::any_container<ssize_t> shape_in,
                detail::any_container<ssize_t> strides_in,
                bool readonly = false)
        : ptr(ptr), itemsize(itemsize), size(1), format(format), ndim(ndim),
          shape(std::move(shape_in)), strides(std::move(strides_in)), readonly(readonly) {
        if (ndim != (ssize_t) shape.size() || ndim != (ssize_t) strides.size()) {
            pybind11_fail("buffer_info: ndim doesn't match shape and/or strides length");
        }
        for (size_t i = 0; i < (size_t) ndim; ++i) {
            size *= shape[i];
        }
    }
 
    template <typename T>
    buffer_info(T *ptr,
                detail::any_container<ssize_t> shape_in,
                detail::any_container<ssize_t> strides_in,
                bool readonly = false)
        : buffer_info(private_ctr_tag(),
                      ptr,
                      sizeof(T),
                      format_descriptor<T>::format(),
                      static_cast<ssize_t>(shape_in->size()),
                      std::move(shape_in),
                      std::move(strides_in),
                      readonly) {}
 
    buffer_info(void *ptr,
                ssize_t itemsize,
                const std::string &format,
                ssize_t size,
                bool readonly = false)
        : buffer_info(ptr, itemsize, format, 1, {size}, {itemsize}, readonly) {}
 
    template <typename T>
    buffer_info(T *ptr, ssize_t size, bool readonly = false)
        : buffer_info(ptr, sizeof(T), format_descriptor<T>::format(), size, readonly) {}
 
    template <typename T>
    buffer_info(const T *ptr, ssize_t size, bool readonly = true)
        : buffer_info(
              const_cast<T *>(ptr), sizeof(T), format_descriptor<T>::format(), size, readonly) {}
 
    explicit buffer_info(Py_buffer *view, bool ownview = true)
        : buffer_info(
              view->buf,
              view->itemsize,
              view->format,
              view->ndim,
              {view->shape, view->shape + view->ndim},
              /* Though buffer::request() requests PyBUF_STRIDES, ctypes objects
               * ignore this flag and return a view with NULL strides.
               * When strides are NULL, build them manually.  */
              view->strides
                  ? std::vector<ssize_t>(view->strides, view->strides + view->ndim)
                  : detail::c_strides({view->shape, view->shape + view->ndim}, view->itemsize),
              (view->readonly != 0)) {
        // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
        this->m_view = view;
        // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
        this->ownview = ownview;
    }
 
    buffer_info(const buffer_info &) = delete;
    buffer_info &operator=(const buffer_info &) = delete;
 
    buffer_info(buffer_info &&other) noexcept { (*this) = std::move(other); }
 
    buffer_info &operator=(buffer_info &&rhs) noexcept {
        ptr = rhs.ptr;
        itemsize = rhs.itemsize;
        size = rhs.size;
        format = std::move(rhs.format);
        ndim = rhs.ndim;
        shape = std::move(rhs.shape);
        strides = std::move(rhs.strides);
        std::swap(m_view, rhs.m_view);
        std::swap(ownview, rhs.ownview);
        readonly = rhs.readonly;
        return *this;
    }
 
    ~buffer_info() {
        if (m_view && ownview) {
            PyBuffer_Release(m_view);
            delete m_view;
        }
    }
 
    Py_buffer *view() const { return m_view; }
    Py_buffer *&view() { return m_view; }
 
    /* True if the buffer item type is equivalent to `T`. */
    // To define "equivalent" by example:
    // `buffer_info::item_type_is_equivalent_to<int>(b)` and
    // `buffer_info::item_type_is_equivalent_to<long>(b)` may both be true
    // on some platforms, but `int` and `unsigned` will never be equivalent.
    // For the ground truth, please inspect `detail::compare_buffer_info<>`.
    template <typename T>
    bool item_type_is_equivalent_to() const {
        return detail::compare_buffer_info<T>::compare(*this);
    }
 
private:
    struct private_ctr_tag {};
 
    buffer_info(private_ctr_tag,
                void *ptr,
                ssize_t itemsize,
                const std::string &format,
                ssize_t ndim,
                detail::any_container<ssize_t> &&shape_in,
                detail::any_container<ssize_t> &&strides_in,
                bool readonly)
        : buffer_info(
              ptr, itemsize, format, ndim, std::move(shape_in), std::move(strides_in), readonly) {}
 
    Py_buffer *m_view = nullptr;
    bool ownview = false;
};
 
PYBIND11_NAMESPACE_BEGIN(detail)
 
template <typename T, typename SFINAE>
struct compare_buffer_info {
    static bool compare(const buffer_info &b) {
        // NOLINTNEXTLINE(bugprone-sizeof-expression) Needed for `PyObject *`
        return b.format == format_descriptor<T>::format() && b.itemsize == (ssize_t) sizeof(T);
    }
};
 
template <typename T>
struct compare_buffer_info<T, detail::enable_if_t<std::is_integral<T>::value>> {
    static bool compare(const buffer_info &b) {
        return (size_t) b.itemsize == sizeof(T)
               && (b.format == format_descriptor<T>::value
                   || ((sizeof(T) == sizeof(long))
                       && b.format == (std::is_unsigned<T>::value ? "L" : "l"))
                   || ((sizeof(T) == sizeof(size_t))
                       && b.format == (std::is_unsigned<T>::value ? "N" : "n")));
    }
};
 
PYBIND11_NAMESPACE_END(detail)
PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)