buffer_info.h

Go to the documentation of this file.

/*
    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;
}
 
PYBIND11_NAMESPACE_END(detail)
 
/// Information record describing a Python buffer object
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) {
        this->m_view = view;
        this->ownview = ownview;
    }
 
    buffer_info(const buffer_info &) = delete;
    buffer_info& operator=(const buffer_info &) = delete;
 
    buffer_info(buffer_info &&other) {
        (*this) = std::move(other);
    }
 
    buffer_info& operator=(buffer_info &&rhs) {
        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; }
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 = void> struct compare_buffer_info {
    static bool compare(const buffer_info& b) {
        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)