include/pybind11/buffer_info.h

0001 /*
0002     pybind11/buffer_info.h: Python buffer object interface
0003
0004     Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
0005
0006     All rights reserved. Use of this source code is governed by a
0007     BSD-style license that can be found in the LICENSE file.
0008 */
0009
0010 #pragma once
0011
0012 #include "detail/common.h"
0013
0014 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
0015
0016 PYBIND11_NAMESPACE_BEGIN(detail)
0017
0018 // Default, C-style strides
0019 inline std::vector<ssize_t> c_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
0020     auto ndim = shape.size();
0021     std::vector<ssize_t> strides(ndim, itemsize);
0022     if (ndim > 0) {
0023         for (size_t i = ndim - 1; i > 0; --i) {
0024             strides[i - 1] = strides[i] * shape[i];
0025         }
0026     }
0027     return strides;
0028 }
0029
0030 // F-style strides; default when constructing an array_t with `ExtraFlags & f_style`
0031 inline std::vector<ssize_t> f_strides(const std::vector<ssize_t> &shape, ssize_t itemsize) {
0032     auto ndim = shape.size();
0033     std::vector<ssize_t> strides(ndim, itemsize);
0034     for (size_t i = 1; i < ndim; ++i) {
0035         strides[i] = strides[i - 1] * shape[i - 1];
0036     }
0037     return strides;
0038 }
0039
0040 template <typename T, typename SFINAE = void>
0041 struct compare_buffer_info;
0042
0043 PYBIND11_NAMESPACE_END(detail)
0044
0045 /// Information record describing a Python buffer object
0046 struct buffer_info {
0047     void *ptr = nullptr;          // Pointer to the underlying storage
0048     ssize_t itemsize = 0;         // Size of individual items in bytes
0049     ssize_t size = 0;             // Total number of entries
0050     std::string format;           // For homogeneous buffers, this should be set to
0051                                   // format_descriptor<T>::format()
0052     ssize_t ndim = 0;             // Number of dimensions
0053     std::vector<ssize_t> shape;   // Shape of the tensor (1 entry per dimension)
0054     std::vector<ssize_t> strides; // Number of bytes between adjacent entries
0055                                   // (for each per dimension)
0056     bool readonly = false;        // flag to indicate if the underlying storage may be written to
0057
0058     buffer_info() = default;
0059
0060     buffer_info(void *ptr,
0061                 ssize_t itemsize,
0062                 const std::string &format,
0063                 ssize_t ndim,
0064                 detail::any_container<ssize_t> shape_in,
0065                 detail::any_container<ssize_t> strides_in,
0066                 bool readonly = false)
0067         : ptr(ptr), itemsize(itemsize), size(1), format(format), ndim(ndim),
0068           shape(std::move(shape_in)), strides(std::move(strides_in)), readonly(readonly) {
0069         if (ndim != (ssize_t) shape.size() || ndim != (ssize_t) strides.size()) {
0070             pybind11_fail("buffer_info: ndim doesn't match shape and/or strides length");
0071         }
0072         for (size_t i = 0; i < (size_t) ndim; ++i) {
0073             size *= shape[i];
0074         }
0075     }
0076
0077     template <typename T>
0078     buffer_info(T *ptr,
0079                 detail::any_container<ssize_t> shape_in,
0080                 detail::any_container<ssize_t> strides_in,
0081                 bool readonly = false)
0082         : buffer_info(private_ctr_tag(),
0083                       ptr,
0084                       sizeof(T),
0085                       format_descriptor<T>::format(),
0086                       static_cast<ssize_t>(shape_in->size()),
0087                       std::move(shape_in),
0088                       std::move(strides_in),
0089                       readonly) {}
0090
0091     buffer_info(void *ptr,
0092                 ssize_t itemsize,
0093                 const std::string &format,
0094                 ssize_t size,
0095                 bool readonly = false)
0096         : buffer_info(ptr, itemsize, format, 1, {size}, {itemsize}, readonly) {}
0097
0098     template <typename T>
0099     buffer_info(T *ptr, ssize_t size, bool readonly = false)
0100         : buffer_info(ptr, sizeof(T), format_descriptor<T>::format(), size, readonly) {}
0101
0102     template <typename T>
0103     buffer_info(const T *ptr, ssize_t size, bool readonly = true)
0104         : buffer_info(
0105               const_cast<T *>(ptr), sizeof(T), format_descriptor<T>::format(), size, readonly) {}
0106
0107     explicit buffer_info(Py_buffer *view, bool ownview = true)
0108         : buffer_info(
0109               view->buf,
0110               view->itemsize,
0111               view->format,
0112               view->ndim,
0113               {view->shape, view->shape + view->ndim},
0114               /* Though buffer::request() requests PyBUF_STRIDES, ctypes objects
0115                * ignore this flag and return a view with NULL strides.
0116                * When strides are NULL, build them manually.  */
0117               view->strides
0118                   ? std::vector<ssize_t>(view->strides, view->strides + view->ndim)
0119                   : detail::c_strides({view->shape, view->shape + view->ndim}, view->itemsize),
0120               (view->readonly != 0)) {
0121         // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
0122         this->m_view = view;
0123         // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
0124         this->ownview = ownview;
0125     }
0126
0127     buffer_info(const buffer_info &) = delete;
0128     buffer_info &operator=(const buffer_info &) = delete;
0129
0130     buffer_info(buffer_info &&other) noexcept { (*this) = std::move(other); }
0131
0132     buffer_info &operator=(buffer_info &&rhs) noexcept {
0133         ptr = rhs.ptr;
0134         itemsize = rhs.itemsize;
0135         size = rhs.size;
0136         format = std::move(rhs.format);
0137         ndim = rhs.ndim;
0138         shape = std::move(rhs.shape);
0139         strides = std::move(rhs.strides);
0140         std::swap(m_view, rhs.m_view);
0141         std::swap(ownview, rhs.ownview);
0142         readonly = rhs.readonly;
0143         return *this;
0144     }
0145
0146     ~buffer_info() {
0147         if (m_view && ownview) {
0148             PyBuffer_Release(m_view);
0149             delete m_view;
0150         }
0151     }
0152
0153     Py_buffer *view() const { return m_view; }
0154     Py_buffer *&view() { return m_view; }
0155
0156     /* True if the buffer item type is equivalent to `T`. */
0157     // To define "equivalent" by example:
0158     // `buffer_info::item_type_is_equivalent_to<int>(b)` and
0159     // `buffer_info::item_type_is_equivalent_to<long>(b)` may both be true
0160     // on some platforms, but `int` and `unsigned` will never be equivalent.
0161     // For the ground truth, please inspect `detail::compare_buffer_info<>`.
0162     template <typename T>
0163     bool item_type_is_equivalent_to() const {
0164         return detail::compare_buffer_info<T>::compare(*this);
0165     }
0166
0167 private:
0168     struct private_ctr_tag {};
0169
0170     buffer_info(private_ctr_tag,
0171                 void *ptr,
0172                 ssize_t itemsize,
0173                 const std::string &format,
0174                 ssize_t ndim,
0175                 detail::any_container<ssize_t> &&shape_in,
0176                 detail::any_container<ssize_t> &&strides_in,
0177                 bool readonly)
0178         : buffer_info(
0179               ptr, itemsize, format, ndim, std::move(shape_in), std::move(strides_in), readonly) {}
0180
0181     Py_buffer *m_view = nullptr;
0182     bool ownview = false;
0183 };
0184
0185 PYBIND11_NAMESPACE_BEGIN(detail)
0186
0187 template <typename T, typename SFINAE>
0188 struct compare_buffer_info {
0189     static bool compare(const buffer_info &b) {
0190         // NOLINTNEXTLINE(bugprone-sizeof-expression) Needed for `PyObject *`
0191         return b.format == format_descriptor<T>::format() && b.itemsize == (ssize_t) sizeof(T);
0192     }
0193 };
0194
0195 template <typename T>
0196 struct compare_buffer_info<T, detail::enable_if_t<std::is_integral<T>::value>> {
0197     static bool compare(const buffer_info &b) {
0198         return (size_t) b.itemsize == sizeof(T)
0199                && (b.format == format_descriptor<T>::value
0200                    || ((sizeof(T) == sizeof(long))
0201                        && b.format == (std::is_unsigned<T>::value ? "L" : "l"))
0202                    || ((sizeof(T) == sizeof(size_t))
0203                        && b.format == (std::is_unsigned<T>::value ? "N" : "n")));
0204     }
0205 };
0206
0207 PYBIND11_NAMESPACE_END(detail)
0208 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)