ref: 12fa017f3fc2687d3afb166fd30d9b134abb1da5
dir: /sys/src/cmd/python/Objects/rangeobject.c/
/* Range object implementation */ #include "Python.h" typedef struct { PyObject_HEAD long start; long step; long len; } rangeobject; /* Return number of items in range/xrange (lo, hi, step). step > 0 * required. Return a value < 0 if & only if the true value is too * large to fit in a signed long. */ static long get_len_of_range(long lo, long hi, long step) { /* ------------------------------------------------------------- If lo >= hi, the range is empty. Else if n values are in the range, the last one is lo + (n-1)*step, which must be <= hi-1. Rearranging, n <= (hi - lo - 1)/step + 1, so taking the floor of the RHS gives the proper value. Since lo < hi in this case, hi-lo-1 >= 0, so the RHS is non-negative and so truncation is the same as the floor. Letting M be the largest positive long, the worst case for the RHS numerator is hi=M, lo=-M-1, and then hi-lo-1 = M-(-M-1)-1 = 2*M. Therefore unsigned long has enough precision to compute the RHS exactly. ---------------------------------------------------------------*/ long n = 0; if (lo < hi) { unsigned long uhi = (unsigned long)hi; unsigned long ulo = (unsigned long)lo; unsigned long diff = uhi - ulo - 1; n = (long)(diff / (unsigned long)step + 1); } return n; } static PyObject * range_new(PyTypeObject *type, PyObject *args, PyObject *kw) { rangeobject *obj; long ilow = 0, ihigh = 0, istep = 1; long n; if (!_PyArg_NoKeywords("xrange()", kw)) return NULL; if (PyTuple_Size(args) <= 1) { if (!PyArg_ParseTuple(args, "l;xrange() requires 1-3 int arguments", &ihigh)) return NULL; } else { if (!PyArg_ParseTuple(args, "ll|l;xrange() requires 1-3 int arguments", &ilow, &ihigh, &istep)) return NULL; } if (istep == 0) { PyErr_SetString(PyExc_ValueError, "xrange() arg 3 must not be zero"); return NULL; } if (istep > 0) n = get_len_of_range(ilow, ihigh, istep); else n = get_len_of_range(ihigh, ilow, -istep); if (n < 0) { PyErr_SetString(PyExc_OverflowError, "xrange() result has too many items"); return NULL; } obj = PyObject_New(rangeobject, &PyRange_Type); if (obj == NULL) return NULL; obj->start = ilow; obj->len = n; obj->step = istep; return (PyObject *) obj; } PyDoc_STRVAR(range_doc, "xrange([start,] stop[, step]) -> xrange object\n\ \n\ Like range(), but instead of returning a list, returns an object that\n\ generates the numbers in the range on demand. For looping, this is \n\ slightly faster than range() and more memory efficient."); static PyObject * range_item(rangeobject *r, Py_ssize_t i) { if (i < 0 || i >= r->len) { PyErr_SetString(PyExc_IndexError, "xrange object index out of range"); return NULL; } return PyInt_FromSsize_t(r->start + (i % r->len) * r->step); } static Py_ssize_t range_length(rangeobject *r) { return (Py_ssize_t)(r->len); } static PyObject * range_repr(rangeobject *r) { PyObject *rtn; if (r->start == 0 && r->step == 1) rtn = PyString_FromFormat("xrange(%ld)", r->start + r->len * r->step); else if (r->step == 1) rtn = PyString_FromFormat("xrange(%ld, %ld)", r->start, r->start + r->len * r->step); else rtn = PyString_FromFormat("xrange(%ld, %ld, %ld)", r->start, r->start + r->len * r->step, r->step); return rtn; } static PySequenceMethods range_as_sequence = { (lenfunc)range_length, /* sq_length */ 0, /* sq_concat */ 0, /* sq_repeat */ (ssizeargfunc)range_item, /* sq_item */ 0, /* sq_slice */ }; static PyObject * range_iter(PyObject *seq); static PyObject * range_reverse(PyObject *seq); PyDoc_STRVAR(reverse_doc, "Returns a reverse iterator."); static PyMethodDef range_methods[] = { {"__reversed__", (PyCFunction)range_reverse, METH_NOARGS, reverse_doc}, {NULL, NULL} /* sentinel */ }; PyTypeObject PyRange_Type = { PyObject_HEAD_INIT(&PyType_Type) 0, /* Number of items for varobject */ "xrange", /* Name of this type */ sizeof(rangeobject), /* Basic object size */ 0, /* Item size for varobject */ (destructor)PyObject_Del, /* tp_dealloc */ 0, /* tp_print */ 0, /* tp_getattr */ 0, /* tp_setattr */ 0, /* tp_compare */ (reprfunc)range_repr, /* tp_repr */ 0, /* tp_as_number */ &range_as_sequence, /* 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, /* tp_flags */ range_doc, /* tp_doc */ 0, /* tp_traverse */ 0, /* tp_clear */ 0, /* tp_richcompare */ 0, /* tp_weaklistoffset */ range_iter, /* tp_iter */ 0, /* tp_iternext */ range_methods, /* tp_methods */ 0, /* tp_members */ 0, /* tp_getset */ 0, /* tp_base */ 0, /* tp_dict */ 0, /* tp_descr_get */ 0, /* tp_descr_set */ 0, /* tp_dictoffset */ 0, /* tp_init */ 0, /* tp_alloc */ range_new, /* tp_new */ }; /*********************** Xrange Iterator **************************/ typedef struct { PyObject_HEAD long index; long start; long step; long len; } rangeiterobject; static PyObject * rangeiter_next(rangeiterobject *r) { if (r->index < r->len) return PyInt_FromLong(r->start + (r->index++) * r->step); return NULL; } static PyObject * rangeiter_len(rangeiterobject *r) { return PyInt_FromLong(r->len - r->index); } PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(it))."); static PyMethodDef rangeiter_methods[] = { {"__length_hint__", (PyCFunction)rangeiter_len, METH_NOARGS, length_hint_doc}, {NULL, NULL} /* sentinel */ }; static PyTypeObject Pyrangeiter_Type = { PyObject_HEAD_INIT(&PyType_Type) 0, /* ob_size */ "rangeiterator", /* tp_name */ sizeof(rangeiterobject), /* tp_basicsize */ 0, /* tp_itemsize */ /* methods */ (destructor)PyObject_Del, /* tp_dealloc */ 0, /* tp_print */ 0, /* tp_getattr */ 0, /* tp_setattr */ 0, /* tp_compare */ 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, /* tp_flags */ 0, /* tp_doc */ 0, /* tp_traverse */ 0, /* tp_clear */ 0, /* tp_richcompare */ 0, /* tp_weaklistoffset */ PyObject_SelfIter, /* tp_iter */ (iternextfunc)rangeiter_next, /* tp_iternext */ rangeiter_methods, /* tp_methods */ 0, }; static PyObject * range_iter(PyObject *seq) { rangeiterobject *it; if (!PyRange_Check(seq)) { PyErr_BadInternalCall(); return NULL; } it = PyObject_New(rangeiterobject, &Pyrangeiter_Type); if (it == NULL) return NULL; it->index = 0; it->start = ((rangeobject *)seq)->start; it->step = ((rangeobject *)seq)->step; it->len = ((rangeobject *)seq)->len; return (PyObject *)it; } static PyObject * range_reverse(PyObject *seq) { rangeiterobject *it; long start, step, len; if (!PyRange_Check(seq)) { PyErr_BadInternalCall(); return NULL; } it = PyObject_New(rangeiterobject, &Pyrangeiter_Type); if (it == NULL) return NULL; start = ((rangeobject *)seq)->start; step = ((rangeobject *)seq)->step; len = ((rangeobject *)seq)->len; it->index = 0; it->start = start + (len-1) * step; it->step = -step; it->len = len; return (PyObject *)it; }