diff options
Diffstat (limited to 'doc/neps')
| -rw-r--r-- | doc/neps/new-iterator-ufunc.rst | 77 |
1 files changed, 55 insertions, 22 deletions
diff --git a/doc/neps/new-iterator-ufunc.rst b/doc/neps/new-iterator-ufunc.rst index 59de93acd..4c1559ace 100644 --- a/doc/neps/new-iterator-ufunc.rst +++ b/doc/neps/new-iterator-ufunc.rst @@ -381,12 +381,46 @@ The proposed ‘order=’ flags become as follows: ‘K’ a layout equivalent to ‘C’ followed by some permutation of the axes, as close to the layout of the input(s) as possible (“Keep Layout”) === ===================================================================================== +Or as an enum:: + + /* For specifying array memory layout or iteration order */ + typedef enum { + /* Fortran order if inputs are all Fortran, C otherwise */ + NPY_ANYORDER=-1, + /* C order */ + NPY_CORDER=0, + /* Fortran order */ + NPY_FORTRANORDER=1, + /* An order as close to the inputs as possible */ + NPY_KEEPORDER=2 + } NPY_ORDER; + + Perhaps a good strategy is to first implement the capabilities discussed here without changing the defaults. Once they are implemented and well-tested, the defaults can change from ``order='C'`` to ``order='K'`` everywhere appropriate. UFuncs additionally should gain an ``order=`` parameter to control the layout of their output(s). +The iterator can do automatic casting, and I have created a sequence +of more permissive casting rules. Perhaps for 2.0, NumPy could adopt +this enum as its prefered way of dealing with casting.:: + + /* For specifying allowed casting in operations which support it */ + typedef enum { + /* Only allow exactly equivalent types */ + NPY_NO_CASTING=0, + /* Allow casts between equivalent types of different byte orders */ + NPY_EQUIV_CASTING=0, + /* Only allow safe casts */ + NPY_SAFE_CASTING=1, + /* Allow safe casts or casts within the same kind */ + NPY_SAME_KIND_CASTING=2, + /* Allow any casts */ + NPY_UNSAFE_CASTING=3 + } NPY_CASTING; + + Iterator Rewrite ================ @@ -629,7 +663,7 @@ the API. We do this with a typedef of an incomplete struct Construction and Destruction ---------------------------- -``NpyIter* NpyIter_New(PyArrayObject* op, npy_uint32 flags, NPY_ORDER order, PyArray_Descr* dtype, npy_intp a_ndim, npy_intp *axes, npy_intp buffersize)`` +``NpyIter* NpyIter_New(PyArrayObject* op, npy_uint32 flags, NPY_ORDER order, NPY_CASTING casting, PyArray_Descr* dtype, npy_intp a_ndim, npy_intp *axes, npy_intp buffersize)`` Creates an iterator for the given numpy array object ``op``. @@ -641,6 +675,12 @@ Construction and Destruction efficient iteration, ``NPY_KEEPORDER`` is the best option, and the other orders enforce the particular iteration pattern. + Any of the ``NPY_CASTING`` enum values may be passed to ``casting``. + The values include ``NPY_NO_CASTING``, ``NPY_EQUIV_CASTING``, + ``NPY_SAFE_CASTING``, ``NPY_SAME_KIND_CASTING``, and + ``NPY_UNSAFE_CASTING``. To allow the casts to occur, copying or + buffering must also be enabled. + If ``dtype`` isn't ``NULL``, then it requires that data type. If copying is allowed, it will make a temporary copy if the data is castable. If ``UPDATEIFCOPY`` is enabled, it will also copy @@ -661,7 +701,7 @@ Construction and Destruction To make an iterator similar to the old iterator, this should work.:: iter = NpyIter_New(op, NPY_ITER_READWRITE, - NPY_CORDER, NULL, 0, NULL); + NPY_CORDER, NPY_NO_CASTING, NULL, 0, NULL); If you want to edit an array with aligned ``double`` code, but the order doesn't matter, you would use this.:: @@ -669,13 +709,13 @@ Construction and Destruction dtype = PyArray_DescrFromType(NPY_DOUBLE); iter = NpyIter_New(op, NPY_ITER_READWRITE | NPY_ITER_BUFFERED | - NPY_ITER_SAME_KIND_CASTS | NPY_ITER_NBO_ALIGNED, NPY_KEEPORDER, + NPY_SAME_KIND_CASTING, dtype, 0, NULL); Py_DECREF(dtype); -``NpyIter* NpyIter_MultiNew(npy_intp niter, PyArrayObject** op, npy_uint32 flags, NPY_ORDER order, npy_uint32 *op_flags, PyArray_Descr** op_dtypes, npy_intp oa_ndim, npy_intp **op_axes, npy_intp buffersize)`` +``NpyIter* NpyIter_MultiNew(npy_intp niter, PyArrayObject** op, npy_uint32 flags, NPY_ORDER order, NPY_CASTING casting, npy_uint32 *op_flags, PyArray_Descr** op_dtypes, npy_intp oa_ndim, npy_intp **op_axes, npy_intp buffersize)`` Creates an iterator for broadcasting the ``niter`` array objects provided in ``op``. @@ -688,6 +728,12 @@ Construction and Destruction efficient iteration, ``NPY_KEEPORDER`` is the best option, and the other orders enforce the particular iteration pattern. + Any of the ``NPY_CASTING`` enum values may be passed to ``casting``. + The values include ``NPY_NO_CASTING``, ``NPY_EQUIV_CASTING``, + ``NPY_SAFE_CASTING``, ``NPY_SAME_KIND_CASTING``, and + ``NPY_UNSAFE_CASTING``. To allow the casts to occur, copying or + buffering must also be enabled. + If ``op_dtypes`` isn't ``NULL``, it specifies a data type or ``NULL`` for each ``op[i]``. @@ -841,19 +887,6 @@ Construction and Destruction flag overrides it and the requested data type is converted to be native byte order. - ``NPY_ITER_SAFE_CASTS``, ``NPY_ITER_SAME_KIND_CASTS`` - ``NPY_ITER_UNSAFE_CASTS`` - - ``SAFE_CASTS`` means casting which the function - ``PyArray_CanCastSafely`` says is permitted. - ``SAME_KIND_CASTS`` adds to that any casting between types - of the same scalar kind, like ``double`` to ``float``. - ``UNSAFE_CASTS`` allows any casting for which a cast function - exists. - - To allow the casts to occur, copying or buffering must - also be enabled. - ``NPY_ITER_ALLOCATE`` This is for output arrays, and requires that the flag @@ -894,7 +927,7 @@ Construction and Destruction correctly. -``int NpyIter_UpdateIter(NpyIter *iter, npy_intp i, npy_uint32 op_flags, PyArray_Descr *dtype)`` **UNIMPLEMENTED** +``int NpyIter_UpdateIter(NpyIter *iter, npy_intp i, npy_uint32 op_flags, NPY_CASTING casting, PyArray_Descr *dtype)`` **UNIMPLEMENTED** Updates the i-th operand within the iterator to possibly have a new data type or more restrictive flag attributes. A use-case for @@ -914,8 +947,7 @@ Construction and Destruction The flags that may be passed in ``op_flags`` are ``NPY_ITER_COPY``, ``NPY_ITER_UPDATEIFCOPY``, - ``NPY_ITER_NBO_ALIGNED``, ``NPY_ITER_SAFE_CASTS``, - ``NPY_ITER_SAME_KIND_CASTS``, and ``NPY_ITER_UNSAFE_CASTS``. + ``NPY_ITER_NBO_ALIGNED``. ``int NpyIter_RemoveCoords(NpyIter *iter)`` @@ -1125,7 +1157,7 @@ Examples -------- A copy function using the iterator. The ``order`` parameter -is used to force the memory layout of the allocated +is used to control the memory layout of the allocated result. If the input is a reference type, this function will fail. @@ -1157,7 +1189,8 @@ references, and add ``NPY_ITER_WRITEABLE_REFERENCES`` to the flags.:: op_flags[1] = NPY_ITER_WRITEONLY | NPY_ITER_ALLOCATE; /* Construct the iterator */ - iter = NpyIter_MultiNew(2, op, flags, order, op_flags, NULL, 0, NULL); + iter = NpyIter_MultiNew(2, op, flags, order, NPY_NO_CASTING, + op_flags, NULL, 0, NULL); if (iter == NULL) { return NULL; } |