Function NpyIter_GetAxisStrideArray

numpy/core/src/multiarray/nditer_api.c:1293–1328

NUMPY_API * Gets the array of strides for the specified axis. * If the iterator is tracking a multi-index, gets the strides * for the axis specified, otherwise gets the strides for * the iteration axis as Fortran order (fastest-changing axis first). * * Returns NULL if an error occurs. */

 * Returns NULL if an error occurs.
 */
NPY_NO_EXPORT npy_intp *
NpyIter_GetAxisStrideArray(NpyIter *iter, int axis)
{
    npy_uint32 itflags = NIT_ITFLAGS(iter);
    int idim, ndim = NIT_NDIM(iter);
    int nop = NIT_NOP(iter);

    npy_int8 *perm = NIT_PERM(iter);
    NpyIter_AxisData *axisdata = NIT_AXISDATA(iter);
    npy_intp sizeof_axisdata = NIT_AXISDATA_SIZEOF(itflags, ndim, nop);

    if (axis < 0 || axis >= ndim) {
        PyErr_SetString(PyExc_ValueError,
                "axis out of bounds in iterator GetStrideAxisArray");
        return NULL;
    }

    if (itflags&NPY_ITFLAG_HASMULTIINDEX) {
        /* Reverse axis, since the iterator treats them that way */
        axis = ndim-1-axis;

        /* First find the axis in question */
        for (idim = 0; idim < ndim; ++idim, NIT_ADVANCE_AXISDATA(axisdata, 1)) {
            if (perm[idim] == axis || -1 - perm[idim] == axis) {
                return NAD_STRIDES(axisdata);
            }
        }
    }
    else {
        return NAD_STRIDES(NIT_INDEX_AXISDATA(axisdata, axis));
    }

    PyErr_SetString(PyExc_RuntimeError,
            "internal error in iterator perm");
    return  NULL;
}

/*NUMPY_API
 * Get an array of strides which are fixed.  Any strides which may