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 PYBIND11_NAMESPACE_END(detail)
0041
0042 /// Information record describing a Python buffer object
0043 struct buffer_info {
0044     void *ptr = nullptr;          // Pointer to the underlying storage
0045     ssize_t itemsize = 0;         // Size of individual items in bytes
0046     ssize_t size = 0;             // Total number of entries
0047     std::string format;           // For homogeneous buffers, this should be set to
0048                                   // format_descriptor<T>::format()
0049     ssize_t ndim = 0;             // Number of dimensions
0050     std::vector<ssize_t> shape;   // Shape of the tensor (1 entry per dimension)
0051     std::vector<ssize_t> strides; // Number of bytes between adjacent entries
0052                                   // (for each per dimension)
0053     bool readonly = false;        // flag to indicate if the underlying storage may be written to
0054
0055     buffer_info() = default;
0056
0057     buffer_info(void *ptr,
0058                 ssize_t itemsize,
0059                 const std::string &format,
0060                 ssize_t ndim,
0061                 detail::any_container<ssize_t> shape_in,
0062                 detail::any_container<ssize_t> strides_in,
0063                 bool readonly = false)
0064         : ptr(ptr), itemsize(itemsize), size(1), format(format), ndim(ndim),
0065           shape(std::move(shape_in)), strides(std::move(strides_in)), readonly(readonly) {
0066         if (ndim != (ssize_t) shape.size() || ndim != (ssize_t) strides.size()) {
0067             pybind11_fail("buffer_info: ndim doesn't match shape and/or strides length");
0068         }
0069         for (size_t i = 0; i < (size_t) ndim; ++i) {
0070             size *= shape[i];
0071         }
0072     }
0073
0074     template <typename T>
0075     buffer_info(T *ptr,
0076                 detail::any_container<ssize_t> shape_in,
0077                 detail::any_container<ssize_t> strides_in,
0078                 bool readonly = false)
0079         : buffer_info(private_ctr_tag(),
0080                       ptr,
0081                       sizeof(T),
0082                       format_descriptor<T>::format(),
0083                       static_cast<ssize_t>(shape_in->size()),
0084                       std::move(shape_in),
0085                       std::move(strides_in),
0086                       readonly) {}
0087
0088     buffer_info(void *ptr,
0089                 ssize_t itemsize,
0090                 const std::string &format,
0091                 ssize_t size,
0092                 bool readonly = false)
0093         : buffer_info(ptr, itemsize, format, 1, {size}, {itemsize}, readonly) {}
0094
0095     template <typename T>
0096     buffer_info(T *ptr, ssize_t size, bool readonly = false)
0097         : buffer_info(ptr, sizeof(T), format_descriptor<T>::format(), size, readonly) {}
0098
0099     template <typename T>
0100     buffer_info(const T *ptr, ssize_t size, bool readonly = true)
0101         : buffer_info(
0102             const_cast<T *>(ptr), sizeof(T), format_descriptor<T>::format(), size, readonly) {}
0103
0104     explicit buffer_info(Py_buffer *view, bool ownview = true)
0105         : buffer_info(
0106             view->buf,
0107             view->itemsize,
0108             view->format,
0109             view->ndim,
0110             {view->shape, view->shape + view->ndim},
0111             /* Though buffer::request() requests PyBUF_STRIDES, ctypes objects
0112              * ignore this flag and return a view with NULL strides.
0113              * When strides are NULL, build them manually.  */
0114             view->strides
0115                 ? std::vector<ssize_t>(view->strides, view->strides + view->ndim)
0116                 : detail::c_strides({view->shape, view->shape + view->ndim}, view->itemsize),
0117             (view->readonly != 0)) {
0118         // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
0119         this->m_view = view;
0120         // NOLINTNEXTLINE(cppcoreguidelines-prefer-member-initializer)
0121         this->ownview = ownview;
0122     }
0123
0124     buffer_info(const buffer_info &) = delete;
0125     buffer_info &operator=(const buffer_info &) = delete;
0126
0127     buffer_info(buffer_info &&other) noexcept { (*this) = std::move(other); }
0128
0129     buffer_info &operator=(buffer_info &&rhs) noexcept {
0130         ptr = rhs.ptr;
0131         itemsize = rhs.itemsize;
0132         size = rhs.size;
0133         format = std::move(rhs.format);
0134         ndim = rhs.ndim;
0135         shape = std::move(rhs.shape);
0136         strides = std::move(rhs.strides);
0137         std::swap(m_view, rhs.m_view);
0138         std::swap(ownview, rhs.ownview);
0139         readonly = rhs.readonly;
0140         return *this;
0141     }
0142
0143     ~buffer_info() {
0144         if (m_view && ownview) {
0145             PyBuffer_Release(m_view);
0146             delete m_view;
0147         }
0148     }
0149
0150     Py_buffer *view() const { return m_view; }
0151     Py_buffer *&view() { return m_view; }
0152
0153 private:
0154     struct private_ctr_tag {};
0155
0156     buffer_info(private_ctr_tag,
0157                 void *ptr,
0158                 ssize_t itemsize,
0159                 const std::string &format,
0160                 ssize_t ndim,
0161                 detail::any_container<ssize_t> &&shape_in,
0162                 detail::any_container<ssize_t> &&strides_in,
0163                 bool readonly)
0164         : buffer_info(
0165             ptr, itemsize, format, ndim, std::move(shape_in), std::move(strides_in), readonly) {}
0166
0167     Py_buffer *m_view = nullptr;
0168     bool ownview = false;
0169 };
0170
0171 PYBIND11_NAMESPACE_BEGIN(detail)
0172
0173 template <typename T, typename SFINAE = void>
0174 struct compare_buffer_info {
0175     static bool compare(const buffer_info &b) {
0176         return b.format == format_descriptor<T>::format() && b.itemsize == (ssize_t) sizeof(T);
0177     }
0178 };
0179
0180 template <typename T>
0181 struct compare_buffer_info<T, detail::enable_if_t<std::is_integral<T>::value>> {
0182     static bool compare(const buffer_info &b) {
0183         return (size_t) b.itemsize == sizeof(T)
0184                && (b.format == format_descriptor<T>::value
0185                    || ((sizeof(T) == sizeof(long))
0186                        && b.format == (std::is_unsigned<T>::value ? "L" : "l"))
0187                    || ((sizeof(T) == sizeof(size_t))
0188                        && b.format == (std::is_unsigned<T>::value ? "N" : "n")));
0189     }
0190 };
0191
0192 PYBIND11_NAMESPACE_END(detail)
0193 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)