memoryobject.c

/*
 * Memoryview object implementation
 * --------------------------------
 *
 *   This implementation is a complete rewrite contributed by Stefan Krah in
 *   Python 3.3.  Substantial credit goes to Antoine Pitrou (who had already
 *   fortified and rewritten the previous implementation) and Nick Coghlan
 *   (who came up with the idea of the ManagedBuffer) for analyzing the complex
 *   ownership rules.
 *
 */

#include "Python.h"
#include "internal/mem.h"
#include "internal/pystate.h"
#include "pystrhex.h"
#include <stddef.h>


/****************************************************************************/
/*                           ManagedBuffer Object                           */
/****************************************************************************/

/*
   ManagedBuffer Object:
   ---------------------

     The purpose of this object is to facilitate the handling of chained
     memoryviews that have the same underlying exporting object. PEP-3118
     allows the underlying object to change while a view is exported. This
     could lead to unexpected results when constructing a new memoryview
     from an existing memoryview.

     Rather than repeatedly redirecting buffer requests to the original base
     object, all chained memoryviews use a single buffer snapshot. This
     snapshot is generated by the constructor _PyManagedBuffer_FromObject().

   Ownership rules:
   ----------------

     The master buffer inside a managed buffer is filled in by the original
     base object. shape, strides, suboffsets and format are read-only for
     all consumers.

     A memoryview's buffer is a private copy of the exporter's buffer. shape,
     strides and suboffsets belong to the memoryview and are thus writable.

     If a memoryview itself exports several buffers via memory_getbuf(), all
     buffer copies share shape, strides and suboffsets. In this case, the
     arrays are NOT writable.

   Reference count assumptions:
   ----------------------------

     The 'obj' member of a Py_buffer must either be NULL or refer to the
     exporting base object. In the Python codebase, all getbufferprocs
     return a new reference to view.obj (example: bytes_buffer_getbuffer()).

     PyBuffer_Release() decrements view.obj (if non-NULL), so the
     releasebufferprocs must NOT decrement view.obj.
*/


#define CHECK_MBUF_RELEASED(mbuf) \
    if (((_PyManagedBufferObject *)mbuf)->flags&_Py_MANAGED_BUFFER_RELEASED) { \
        PyErr_SetString(PyExc_ValueError,                                      \
            "operation forbidden on released memoryview object");              \
        return NULL;                                                           \
    }


static inline _PyManagedBufferObject *
mbuf_alloc(void)
{
    _PyManagedBufferObject *mbuf;

    mbuf = (_PyManagedBufferObject *)
        PyObject_GC_New(_PyManagedBufferObject, &_PyManagedBuffer_Type);
    if (mbuf == NULL)
        return NULL;
    mbuf->flags = 0;
    mbuf->exports = 0;
    mbuf->master.obj = NULL;
    _PyObject_GC_TRACK(mbuf);

    return mbuf;
}

static PyObject *
_PyManagedBuffer_FromObject(PyObject *base)
{
    _PyManagedBufferObject *mbuf;

    mbuf = mbuf_alloc();
    if (mbuf == NULL)
        return NULL;

    if (PyObject_GetBuffer(base, &mbuf->master, PyBUF_FULL_RO) < 0) {
        mbuf->master.obj = NULL;
        Py_DECREF(mbuf);
        return NULL;
    }

    return (PyObject *)mbuf;
}

static void
mbuf_release(_PyManagedBufferObject *self)
{
    if (self->flags&_Py_MANAGED_BUFFER_RELEASED)
        return;

    /* NOTE: at this point self->exports can still be > 0 if this function
       is called from mbuf_clear() to break up a reference cycle. */
    self->flags |= _Py_MANAGED_BUFFER_RELEASED;

    /* PyBuffer_Release() decrements master->obj and sets it to NULL. */
    _PyObject_GC_UNTRACK(self);
    PyBuffer_Release(&self->master);
}

static void
mbuf_dealloc(_PyManagedBufferObject *self)
{
    assert(self->exports == 0);
    mbuf_release(self);
    if (self->flags&_Py_MANAGED_BUFFER_FREE_FORMAT)
        PyMem_Free(self->master.format);
    PyObject_GC_Del(self);
}

static int
mbuf_traverse(_PyManagedBufferObject *self, visitproc visit, void *arg)
{
    Py_VISIT(self->master.obj);
    return 0;
}

static int
mbuf_clear(_PyManagedBufferObject *self)
{
    assert(self->exports >= 0);
    mbuf_release(self);
    return 0;
}

PyTypeObject _PyManagedBuffer_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "managedbuffer",
    sizeof(_PyManagedBufferObject),
    0,
    (destructor)mbuf_dealloc,                /* tp_dealloc */
    0,                                       /* tp_print */
    0,                                       /* tp_getattr */
    0,                                       /* tp_setattr */
    0,                                       /* tp_reserved */
    0,                                       /* tp_repr */
    0,                                       /* tp_as_number */
    0,                                       /* tp_as_sequence */
    0,                                       /* tp_as_mapping */
    0,                                       /* tp_hash */
    0,                                       /* tp_call */
    0,                                       /* tp_str */
    PyObject_GenericGetAttr,                 /* tp_getattro */
    0,                                       /* tp_setattro */
    0,                                       /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
    0,                                       /* tp_doc */
    (traverseproc)mbuf_traverse,             /* tp_traverse */
    (inquiry)mbuf_clear                      /* tp_clear */
};


/****************************************************************************/
/*                             MemoryView Object                            */
/****************************************************************************/

/* In the process of breaking reference cycles mbuf_release() can be
   called before memory_release(). */
#define BASE_INACCESSIBLE(mv) \
    (((PyMemoryViewObject *)mv)->flags&_Py_MEMORYVIEW_RELEASED || \
     ((PyMemoryViewObject *)mv)->mbuf->flags&_Py_MANAGED_BUFFER_RELEASED)

#define CHECK_RELEASED(mv) \
    if (BASE_INACCESSIBLE(mv)) {                                  \
        PyErr_SetString(PyExc_ValueError,                         \
            "operation forbidden on released memoryview object"); \
        return NULL;                                              \
    }

#define CHECK_RELEASED_INT(mv) \
    if (BASE_INACCESSIBLE(mv)) {                                  \
        PyErr_SetString(PyExc_ValueError,                         \
            "operation forbidden on released memoryview object"); \
        return -1;                                                \
    }

#define CHECK_LIST_OR_TUPLE(v) \
    if (!PyList_Check(v) && !PyTuple_Check(v)) { \
        PyErr_SetString(PyExc_TypeError,         \
            #v " must be a list or a tuple");    \
        return NULL;                             \
    }

#define VIEW_ADDR(mv) (&((PyMemoryViewObject *)mv)->view)

/* Check for the presence of suboffsets in the first dimension. */
#define HAVE_PTR(suboffsets, dim) (suboffsets && suboffsets[dim] >= 0)
/* Adjust ptr if suboffsets are present. */
#define ADJUST_PTR(ptr, suboffsets, dim) \
    (HAVE_PTR(suboffsets, dim) ? *((char**)ptr) + suboffsets[dim] : ptr)

/* Memoryview buffer properties */
#define MV_C_CONTIGUOUS(flags) (flags&(_Py_MEMORYVIEW_SCALAR|_Py_MEMORYVIEW_C))
#define MV_F_CONTIGUOUS(flags) \
    (flags&(_Py_MEMORYVIEW_SCALAR|_Py_MEMORYVIEW_FORTRAN))
#define MV_ANY_CONTIGUOUS(flags) \
    (flags&(_Py_MEMORYVIEW_SCALAR|_Py_MEMORYVIEW_C|_Py_MEMORYVIEW_FORTRAN))

/* Fast contiguity test. Caller must ensure suboffsets==NULL and ndim==1. */
#define MV_CONTIGUOUS_NDIM1(view) \
    ((view)->shape[0] == 1 || (view)->strides[0] == (view)->itemsize)

/* getbuffer() requests */
#define REQ_INDIRECT(flags) ((flags&PyBUF_INDIRECT) == PyBUF_INDIRECT)
#define REQ_C_CONTIGUOUS(flags) ((flags&PyBUF_C_CONTIGUOUS) == PyBUF_C_CONTIGUOUS)
#define REQ_F_CONTIGUOUS(flags) ((flags&PyBUF_F_CONTIGUOUS) == PyBUF_F_CONTIGUOUS)
#define REQ_ANY_CONTIGUOUS(flags) ((flags&PyBUF_ANY_CONTIGUOUS) == PyBUF_ANY_CONTIGUOUS)
#define REQ_STRIDES(flags) ((flags&PyBUF_STRIDES) == PyBUF_STRIDES)
#define REQ_SHAPE(flags) ((flags&PyBUF_ND) == PyBUF_ND)
#define REQ_WRITABLE(flags) (flags&PyBUF_WRITABLE)
#define REQ_FORMAT(flags) (flags&PyBUF_FORMAT)


PyDoc_STRVAR(memory_doc,
"memoryview(object)\n--\n\
\n\
Create a new memoryview object which references the given object.");


/**************************************************************************/
/*                       Copy memoryview buffers                          */
/**************************************************************************/

/* The functions in this section take a source and a destination buffer
   with the same logical structure: format, itemsize, ndim and shape
   are identical, with ndim > 0.

   NOTE: All buffers are assumed to have PyBUF_FULL information, which
   is the case for memoryviews! */


/* Assumptions: ndim >= 1. The macro tests for a corner case that should
   perhaps be explicitly forbidden in the PEP. */
#define HAVE_SUBOFFSETS_IN_LAST_DIM(view) \
    (view->suboffsets && view->suboffsets[dest->ndim-1] >= 0)

static inline int
last_dim_is_contiguous(const Py_buffer *dest, const Py_buffer *src)
{
    assert(dest->ndim > 0 && src->ndim > 0);
    return (!HAVE_SUBOFFSETS_IN_LAST_DIM(dest) &&
            !HAVE_SUBOFFSETS_IN_LAST_DIM(src) &&
            dest->strides[dest->ndim-1] == dest->itemsize &&
            src->strides[src->ndim-1] == src->itemsize);
}

/* This is not a general function for determining format equivalence.
   It is used in copy_single() and copy_buffer() to weed out non-matching
   formats. Skipping the '@' character is specifically used in slice
   assignments, where the lvalue is already known to have a single character
   format. This is a performance hack that could be rewritten (if properly
   benchmarked). */
static inline int
equiv_format(const Py_buffer *dest, const Py_buffer *src)
{
    const char *dfmt, *sfmt;

    assert(dest->format && src->format);
    dfmt = dest->format[0] == '@' ? dest->format+1 : dest->format;
    sfmt = src->format[0] == '@' ? src->format+1 : src->format;

    if (strcmp(dfmt, sfmt) != 0 ||
        dest->itemsize != src->itemsize) {
        return 0;
    }

    return 1;
}

/* Two shapes are equivalent if they are either equal or identical up
   to a zero element at the same position. For example, in NumPy arrays
   the shapes [1, 0, 5] and [1, 0, 7] are equivalent. */
static inline int
equiv_shape(const Py_buffer *dest, const Py_buffer *src)
{
    int i;

    if (dest->ndim != src->ndim)
        return 0;

    for (i = 0; i < dest->ndim; i++) {
        if (dest->shape[i] != src->shape[i])
            return 0;
        if (dest->shape[i] == 0)
            break;
    }

    return 1;
}

/* Check that the logical structure of the destination and source buffers
   is identical. */
static int
equiv_structure(const Py_buffer *dest, const Py_buffer *src)
{
    if (!equiv_format(dest, src) ||
        !equiv_shape(dest, src)) {
        PyErr_SetString(PyExc_ValueError,
            "memoryview assignment: lvalue and rvalue have different "
            "structures");
        return 0;
    }

    return 1;
}

/* Base case for recursive multi-dimensional copying. Contiguous arrays are
   copied with very little overhead. Assumptions: ndim == 1, mem == NULL or
   sizeof(mem) == shape[0] * itemsize. */
static void
copy_base(const Py_ssize_t *shape, Py_ssize_t itemsize,
          char *dptr, const Py_ssize_t *dstrides, const Py_ssize_t *dsuboffsets,
          char *sptr, const Py_ssize_t *sstrides, const Py_ssize_t *ssuboffsets,
          char *mem)
{
    if (mem == NULL) { /* contiguous */
        Py_ssize_t size = shape[0] * itemsize;
        if (dptr + size < sptr || sptr + size < dptr)
            memcpy(dptr, sptr, size); /* no overlapping */
        else
            memmove(dptr, sptr, size);
    }
    else {
        char *p;
        Py_ssize_t i;
        for (i=0, p=mem; i < shape[0]; p+=itemsize, sptr+=sstrides[0], i++) {
            char *xsptr = ADJUST_PTR(sptr, ssuboffsets, 0);
            memcpy(p, xsptr, itemsize);
        }
        for (i=0, p=mem; i < shape[0]; p+=itemsize, dptr+=dstrides[0], i++) {
            char *xdptr = ADJUST_PTR(dptr, dsuboffsets, 0);
            memcpy(xdptr, p, itemsize);
        }
    }

}

/* Recursively copy a source buffer to a destination buffer. The two buffers
   have the same ndim, shape and itemsize. */
static void
copy_rec(const Py_ssize_t *shape, Py_ssize_t ndim, Py_ssize_t itemsize,
         char *dptr, const Py_ssize_t *dstrides, const Py_ssize_t *dsuboffsets,
         char *sptr, const Py_ssize_t *sstrides, const Py_ssize_t *ssuboffsets,
         char *mem)
{
    Py_ssize_t i;

    assert(ndim >= 1);

    if (ndim == 1) {
        copy_base(shape, itemsize,
                  dptr, dstrides, dsuboffsets,
                  sptr, sstrides, ssuboffsets,
                  mem);
        return;
    }

    for (i = 0; i < shape[0]; dptr+=dstrides[0], sptr+=sstrides[0], i++) {
        char *xdptr = ADJUST_PTR(dptr, dsuboffsets, 0);
        char *xsptr = ADJUST_PTR(sptr, ssuboffsets, 0);

        copy_rec(shape+1, ndim-1, itemsize,
                 xdptr, dstrides+1, dsuboffsets ? dsuboffsets+1 : NULL,
                 xsptr, sstrides+1, ssuboffsets ? ssuboffsets+1 : NULL,
                 mem);
    }
}

/* Faster copying of one-dimensional arrays. */
static int
copy_single(Py_buffer *dest, Py_buffer *src)
{
    char *mem = NULL;

    assert(dest->ndim == 1);

    if (!equiv_structure(dest, src))
        return -1;

    if (!last_dim_is_contiguous(dest, src)) {
        mem = PyMem_Malloc(dest->shape[0] * dest->itemsize);
        if (mem == NULL) {
            PyErr_NoMemory();
            return -1;
        }
    }

    copy_base(dest->shape, dest->itemsize,
              dest->buf, dest->strides, dest->suboffsets,
              src->buf, src->strides, src->suboffsets,
              mem);

    if (mem)
        PyMem_Free(mem);

    return 0;
}

/* Recursively copy src to dest. Both buffers must have the same basic
   structure. Copying is atomic, the function never fails with a partial
   copy. */
static int
copy_buffer(Py_buffer *dest, Py_buffer *src)
{
    char *mem = NULL;

    assert(dest->ndim > 0);

    if (!equiv_structure(dest, src))
        return -1;

    if (!last_dim_is_contiguous(dest, src)) {
        mem = PyMem_Malloc(dest->shape[dest->ndim-1] * dest->itemsize);
        if (mem == NULL) {
            PyErr_NoMemory();
            return -1;
        }
    }

    copy_rec(dest->shape, dest->ndim, dest->itemsize,
             dest->buf, dest->strides, dest->suboffsets,
             src->buf, src->strides, src->suboffsets,
             mem);

    if (mem)
        PyMem_Free(mem);

    return 0;
}

/* Initialize strides for a C-contiguous array. */
static inline void
init_strides_from_shape(Py_buffer *view)
{
    Py_ssize_t i;

    assert(view->ndim > 0);

    view->strides[view->ndim-1] = view->itemsize;
    for (i = view->ndim-2; i >= 0; i--)
        view->strides[i] = view->strides[i+1] * view->shape[i+1];
}

/* Initialize strides for a Fortran-contiguous array. */
static inline void
init_fortran_strides_from_shape(Py_buffer *view)
{
    Py_ssize_t i;

    assert(view->ndim > 0);

    view->strides[0] = view->itemsize;
    for (i = 1; i < view->ndim; i++)
        view->strides[i] = view->strides[i-1] * view->shape[i-1];
}

/* Copy src to a contiguous representation. order is one of 'C', 'F' (Fortran)
   or 'A' (Any). Assumptions: src has PyBUF_FULL information, src->ndim >= 1,
   len(mem) == src->len. */
static int
buffer_to_contiguous(char *mem, Py_buffer *src, char order)
{
    Py_buffer dest;
    Py_ssize_t *strides;
    int ret;

    assert(src->ndim >= 1);
    assert(src->shape != NULL);
    assert(src->strides != NULL);

    strides = PyMem_Malloc(src->ndim * (sizeof *src->strides));
    if (strides == NULL) {
        PyErr_NoMemory();
        return -1;
    }

    /* initialize dest */
    dest = *src;
    dest.buf = mem;
    /* shape is constant and shared: the logical representation of the
       array is unaltered. */

    /* The physical representation determined by strides (and possibly
       suboffsets) may change. */
    dest.strides = strides;
    if (order == 'C' || order == 'A') {
        init_strides_from_shape(&dest);
    }
    else {
        init_fortran_strides_from_shape(&dest);
    }

    dest.suboffsets = NULL;

    ret = copy_buffer(&dest, src);

    PyMem_Free(strides);
    return ret;
}


/****************************************************************************/
/*                               Constructors                               */
/****************************************************************************/

/* Initialize values that are shared with the managed buffer. */
static inline void
init_shared_values(Py_buffer *dest, const Py_buffer *src)
{
    dest->obj = src->obj;
    dest->buf = src->buf;
    dest->len = src->len;
    dest->itemsize = src->itemsize;
    dest->readonly = src->readonly;
    dest->format = src->format ? src->format : "B";
    dest->internal = src->internal;
}

/* Copy shape and strides. Reconstruct missing values. */
static void
init_shape_strides(Py_buffer *dest, const Py_buffer *src)
{
    Py_ssize_t i;

    if (src->ndim == 0) {
        dest->shape = NULL;
        dest->strides = NULL;
        return;
    }
    if (src->ndim == 1) {
        dest->shape[0] = src->shape ? src->shape[0] : src->len / src->itemsize;
        dest->strides[0] = src->strides ? src->strides[0] : src->itemsize;
        return;
    }

    for (i = 0; i < src->ndim; i++)
        dest->shape[i] = src->shape[i];
    if (src->strides) {
        for (i = 0; i < src->ndim; i++)
            dest->strides[i] = src->strides[i];
    }
    else {
        init_strides_from_shape(dest);
    }
}

static inline void
init_suboffsets(Py_buffer *dest, const Py_buffer *src)
{
    Py_ssize_t i;

    if (src->suboffsets == NULL) {
        dest->suboffsets = NULL;
        return;
    }
    for (i = 0; i < src->ndim; i++)
        dest->suboffsets[i] = src->suboffsets[i];
}

/* len = product(shape) * itemsize */
static inline void
init_len(Py_buffer *view)
{
    Py_ssize_t i, len;

    len = 1;
    for (i = 0; i < view->ndim; i++)
        len *= view->shape[i];
    len *= view->itemsize;

    view->len = len;
}

/* Initialize memoryview buffer properties. */
static void
init_flags(PyMemoryViewObject *mv)
{
    const Py_buffer *view = &mv->view;
    int flags = 0;

    switch (view->ndim) {
    case 0:
        flags |= (_Py_MEMORYVIEW_SCALAR|_Py_MEMORYVIEW_C|
                  _Py_MEMORYVIEW_FORTRAN);
        break;
    case 1:
        if (MV_CONTIGUOUS_NDIM1(view))
            flags |= (_Py_MEMORYVIEW_C|_Py_MEMORYVIEW_FORTRAN);
        break;
    default:
        if (PyBuffer_IsContiguous(view, 'C'))
            flags |= _Py_MEMORYVIEW_C;
        if (PyBuffer_IsContiguous(view, 'F'))
            flags |= _Py_MEMORYVIEW_FORTRAN;
        break;
    }

    if (view->suboffsets) {
        flags |= _Py_MEMORYVIEW_PIL;
        flags &= ~(_Py_MEMORYVIEW_C|_Py_MEMORYVIEW_FORTRAN);
    }

    mv->flags = flags;
}

/* Allocate a new memoryview and perform basic initialization. New memoryviews
   are exclusively created through the mbuf_add functions. */
static inline PyMemoryViewObject *
memory_alloc(int ndim)
{
    PyMemoryViewObject *mv;

    mv = (PyMemoryViewObject *)
        PyObject_GC_NewVar(PyMemoryViewObject, &PyMemoryView_Type, 3*ndim);
    if (mv == NULL)
        return NULL;

    mv->mbuf = NULL;
    mv->hash = -1;
    mv->flags = 0;
    mv->exports = 0;
    mv->view.ndim = ndim;
    mv->view.shape = mv->ob_array;
    mv->view.strides = mv->ob_array + ndim;
    mv->view.suboffsets = mv->ob_array + 2 * ndim;
    mv->weakreflist = NULL;

    _PyObject_GC_TRACK(mv);
    return mv;
}

/*
   Return a new memoryview that is registered with mbuf. If src is NULL,
   use mbuf->master as the underlying buffer. Otherwise, use src.

   The new memoryview has full buffer information: shape and strides
   are always present, suboffsets as needed. Arrays are copied to
   the memoryview's ob_array field.
 */
static PyObject *
mbuf_add_view(_PyManagedBufferObject *mbuf, const Py_buffer *src)
{
    PyMemoryViewObject *mv;
    Py_buffer *dest;

    if (src == NULL)
        src = &mbuf->master;

    if (src->ndim > PyBUF_MAX_NDIM) {
        PyErr_SetString(PyExc_ValueError,
            "memoryview: number of dimensions must not exceed "
            Py_STRINGIFY(PyBUF_MAX_NDIM));
        return NULL;
    }

    mv = memory_alloc(src->ndim);
    if (mv == NULL)
        return NULL;

    dest = &mv->view;
    init_shared_values(dest, src);
    init_shape_strides(dest, src);
    init_suboffsets(dest, src);
    init_flags(mv);

    mv->mbuf = mbuf;
    Py_INCREF(mbuf);
    mbuf->exports++;

    return (PyObject *)mv;
}

/* Register an incomplete view: shape, strides, suboffsets and flags still
   need to be initialized. Use 'ndim' instead of src->ndim to determine the
   size of the memoryview's ob_array.

   Assumption: ndim <= PyBUF_MAX_NDIM. */
static PyObject *
mbuf_add_incomplete_view(_PyManagedBufferObject *mbuf, const Py_buffer *src,
                         int ndim)
{
    PyMemoryViewObject *mv;
    Py_buffer *dest;

    if (src == NULL)
        src = &mbuf->master;

    assert(ndim <= PyBUF_MAX_NDIM);

    mv = memory_alloc(ndim);
    if (mv == NULL)
        return NULL;

    dest = &mv->view;
    init_shared_values(dest, src);

    mv->mbuf = mbuf;
    Py_INCREF(mbuf);
    mbuf->exports++;

    return (PyObject *)mv;
}

/* Expose a raw memory area as a view of contiguous bytes. flags can be
   PyBUF_READ or PyBUF_WRITE. view->format is set to "B" (unsigned bytes).
   The memoryview has complete buffer information. */
PyObject *
PyMemoryView_FromMemory(char *mem, Py_ssize_t size, int flags)
{
    _PyManagedBufferObject *mbuf;
    PyObject *mv;
    int readonly;

    assert(mem != NULL);
    assert(flags == PyBUF_READ || flags == PyBUF_WRITE);

    mbuf = mbuf_alloc();
    if (mbuf == NULL)
        return NULL;

    readonly = (flags == PyBUF_WRITE) ? 0 : 1;
    (void)PyBuffer_FillInfo(&mbuf->master, NULL, mem, size, readonly,
                            PyBUF_FULL_RO);

    mv = mbuf_add_view(mbuf, NULL);
    Py_DECREF(mbuf);

    return mv;
}

/* Create a memoryview from a given Py_buffer. For simple byte views,
   PyMemoryView_FromMemory() should be used instead.
   This function is the only entry point that can create a master buffer
   without full information. Because of this fact init_shape_strides()
   must be able to reconstruct missing values.  */
PyObject *
PyMemoryView_FromBuffer(Py_buffer *info)
{
    _PyManagedBufferObject *mbuf;
    PyObject *mv;

    if (info->buf == NULL) {
        PyErr_SetString(PyExc_ValueError,
            "PyMemoryView_FromBuffer(): info->buf must not be NULL");
        return NULL;
    }

    mbuf = mbuf_alloc();
    if (mbuf == NULL)
        return NULL;

    /* info->obj is either NULL or a borrowed reference. This reference
       should not be decremented in PyBuffer_Release(). */
    mbuf->master = *info;
    mbuf->master.obj = NULL;

    mv = mbuf_add_view(mbuf, NULL);
    Py_DECREF(mbuf);

    return mv;
}

/* Create a memoryview from an object that implements the buffer protocol.
   If the object is a memoryview, the new memoryview must be registered
   with the same managed buffer. Otherwise, a new managed buffer is created. */
PyObject *
PyMemoryView_FromObject(PyObject *v)
{
    _PyManagedBufferObject *mbuf;

    if (PyMemoryView_Check(v)) {
        PyMemoryViewObject *mv = (PyMemoryViewObject *)v;
        CHECK_RELEASED(mv);
        return mbuf_add_view(mv->mbuf, &mv->view);
    }
    else if (PyObject_CheckBuffer(v)) {
        PyObject *ret;
        mbuf = (_PyManagedBufferObject *)_PyManagedBuffer_FromObject(v);
        if (mbuf == NULL)
            return NULL;
        ret = mbuf_add_view(mbuf, NULL);
        Py_DECREF(mbuf);
        return ret;
    }

    PyErr_Format(PyExc_TypeError,
        "memoryview: a bytes-like object is required, not '%.200s'",
        Py_TYPE(v)->tp_name);
    return NULL;
}

/* Copy the format string from a base object that might vanish. */
static int
mbuf_copy_format(_PyManagedBufferObject *mbuf, const char *fmt)
{
    if (fmt != NULL) {
        char *cp = PyMem_Malloc(strlen(fmt)+1);
        if (cp == NULL) {
            PyErr_NoMemory();
            return -1;
        }
        mbuf->master.format = strcpy(cp, fmt);
        mbuf->flags |= _Py_MANAGED_BUFFER_FREE_FORMAT;
    }

    return 0;
}

/*
   Return a memoryview that is based on a contiguous copy of src.
   Assumptions: src has PyBUF_FULL_RO information, src->ndim > 0.

   Ownership rules:
     1) As usual, the returned memoryview has a private copy
        of src->shape, src->strides and src->suboffsets.
     2) src->format is copied to the master buffer and released
        in mbuf_dealloc(). The releasebufferproc of the bytes
        object is NULL, so it does not matter that mbuf_release()
        passes the altered format pointer to PyBuffer_Release().
*/
static PyObject *
memory_from_contiguous_copy(Py_buffer *src, char order)
{
    _PyManagedBufferObject *mbuf;
    PyMemoryViewObject *mv;
    PyObject *bytes;
    Py_buffer *dest;
    int i;

    assert(src->ndim > 0);
    assert(src->shape != NULL);

    bytes = PyBytes_FromStringAndSize(NULL, src->len);
    if (bytes == NULL)
        return NULL;

    mbuf = (_PyManagedBufferObject *)_PyManagedBuffer_FromObject(bytes);
    Py_DECREF(bytes);
    if (mbuf == NULL)
        return NULL;

    if (mbuf_copy_format(mbuf, src->format) < 0) {
        Py_DECREF(mbuf);
        return NULL;
    }

    mv = (PyMemoryViewObject *)mbuf_add_incomplete_view(mbuf, NULL, src->ndim);
    Py_DECREF(mbuf);
    if (mv == NULL)
        return NULL;

    dest = &mv->view;

    /* shared values are initialized correctly except for itemsize */
    dest->itemsize = src->itemsize;

    /* shape and strides */
    for (i = 0; i < src->ndim; i++) {
        dest->shape[i] = src->shape[i];
    }
    if (order == 'C' || order == 'A') {
        init_strides_from_shape(dest);
    }
    else {
        init_fortran_strides_from_shape(dest);
    }
    /* suboffsets */
    dest->suboffsets = NULL;

    /* flags */
    init_flags(mv);

    if (copy_buffer(dest, src) < 0) {
        Py_DECREF(mv);
        return NULL;
    }

    return (PyObject *)mv;
}

/*
   Return a new memoryview object based on a contiguous exporter with
   buffertype={PyBUF_READ, PyBUF_WRITE} and order={'C', 'F'ortran, or 'A'ny}.
   The logical structure of the input and output buffers is the same
   (i.e. tolist(input) == tolist(output)), but the physical layout in
   memory can be explicitly chosen.

   As usual, if buffertype=PyBUF_WRITE, the exporter's buffer must be writable,
   otherwise it may be writable or read-only.

   If the exporter is already contiguous with the desired target order,
   the memoryview will be directly based on the exporter.

   Otherwise, if the buffertype is PyBUF_READ, the memoryview will be
   based on a new bytes object. If order={'C', 'A'ny}, use 'C' order,
   'F'ortran order otherwise.
*/
PyObject *
PyMemoryView_GetContiguous(PyObject *obj, int buffertype, char order)
{
    PyMemoryViewObject *mv;
    PyObject *ret;
    Py_buffer *view;

    assert(buffertype == PyBUF_READ || buffertype == PyBUF_WRITE);
    assert(order == 'C' || order == 'F' || order == 'A');

    mv = (PyMemoryViewObject *)PyMemoryView_FromObject(obj);
    if (mv == NULL)
        return NULL;

    view = &mv->view;
    if (buffertype == PyBUF_WRITE && view->readonly) {
        PyErr_SetString(PyExc_BufferError,
            "underlying buffer is not writable");
        Py_DECREF(mv);
        return NULL;
    }

    if (PyBuffer_IsContiguous(view, order))
        return (PyObject *)mv;

    if (buffertype == PyBUF_WRITE) {
        PyErr_SetString(PyExc_BufferError,
            "writable contiguous buffer requested "
            "for a non-contiguous object.");
        Py_DECREF(mv);
        return NULL;
    }

    ret = memory_from_contiguous_copy(view, order);
    Py_DECREF(mv);
    return ret;
}


static PyObject *
memory_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds)
{
    PyObject *obj;
    static char *kwlist[] = {"object", NULL};

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O:memoryview", kwlist,
                                     &obj)) {
        return NULL;
    }

    return PyMemoryView_FromObject(obj);
}


/****************************************************************************/
/*                         Previously in abstract.c                         */
/****************************************************************************/

typedef struct {
    Py_buffer view;
    Py_ssize_t array[1];
} Py_buffer_full;

int
PyBuffer_ToContiguous(void *buf, Py_buffer *src, Py_ssize_t len, char order)
{
    Py_buffer_full *fb = NULL;
    int ret;

    assert(order == 'C' || order == 'F' || order == 'A');

    if (len != src->len) {
        PyErr_SetString(PyExc_ValueError,
            "PyBuffer_ToContiguous: len != view->len");
        return -1;
    }

    if (PyBuffer_IsContiguous(src, order)) {
        memcpy((char *)buf, src->buf, len);
        return 0;
    }