Function NpyIter_GotoIndex

numpy/core/src/multiarray/nditer_api.c:531–611

NUMPY_API * If the iterator is tracking an index, sets the iterator * to the specified index. * * Returns NPY_SUCCEED on success, NPY_FAIL on failure. */

 * Returns NPY_SUCCEED on success, NPY_FAIL on failure.
 */
NPY_NO_EXPORT int
NpyIter_GotoIndex(NpyIter *iter, npy_intp flat_index)
{
    npy_uint32 itflags = NIT_ITFLAGS(iter);
    int idim, ndim = NIT_NDIM(iter);
    int nop = NIT_NOP(iter);

    npy_intp iterindex, factor;
    NpyIter_AxisData *axisdata;
    npy_intp sizeof_axisdata;

    if (!(itflags&NPY_ITFLAG_HASINDEX)) {
        PyErr_SetString(PyExc_ValueError,
                "Cannot call GotoIndex on an iterator without "
                "requesting a C or Fortran index in the constructor");
        return NPY_FAIL;
    }

    if (itflags&NPY_ITFLAG_BUFFER) {
        PyErr_SetString(PyExc_ValueError,
                "Cannot call GotoIndex on an iterator which "
                "is buffered");
        return NPY_FAIL;
    }

    if (itflags&NPY_ITFLAG_EXLOOP) {
        PyErr_SetString(PyExc_ValueError,
                "Cannot call GotoIndex on an iterator which "
                "has the flag EXTERNAL_LOOP");
        return NPY_FAIL;
    }

    if (flat_index < 0 || flat_index >= NIT_ITERSIZE(iter)) {
        PyErr_SetString(PyExc_IndexError,
                "Iterator GotoIndex called with an out-of-bounds "
                "index");
        return NPY_FAIL;
    }

    axisdata = NIT_AXISDATA(iter);
    sizeof_axisdata = NIT_AXISDATA_SIZEOF(itflags, ndim, nop);

    /* Compute the iterindex corresponding to the flat_index */
    iterindex = 0;
    factor = 1;
    for (idim = 0; idim < ndim; ++idim) {
        npy_intp i, shape, iterstride;

        iterstride = NAD_STRIDES(axisdata)[nop];
        shape = NAD_SHAPE(axisdata);

        /* Extract the index from the flat_index */
        if (iterstride == 0) {
            i = 0;
        }
        else if (iterstride < 0) {
            i = shape - (flat_index/(-iterstride))%shape - 1;
        }