347 lines
12 KiB
C
347 lines
12 KiB
C
/* Range object implementation */
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#include "Python.h"
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typedef struct {
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PyObject_HEAD
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long start;
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long step;
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long len;
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} rangeobject;
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/* Return number of items in range (lo, hi, step). step != 0
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* required. The result always fits in an unsigned long.
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*/
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static unsigned long
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get_len_of_range(long lo, long hi, long step)
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{
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/* -------------------------------------------------------------
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If step > 0 and lo >= hi, or step < 0 and lo <= hi, the range is empty.
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Else for step > 0, if n values are in the range, the last one is
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lo + (n-1)*step, which must be <= hi-1. Rearranging,
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n <= (hi - lo - 1)/step + 1, so taking the floor of the RHS gives
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the proper value. Since lo < hi in this case, hi-lo-1 >= 0, so
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the RHS is non-negative and so truncation is the same as the
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floor. Letting M be the largest positive long, the worst case
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for the RHS numerator is hi=M, lo=-M-1, and then
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hi-lo-1 = M-(-M-1)-1 = 2*M. Therefore unsigned long has enough
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precision to compute the RHS exactly. The analysis for step < 0
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is similar.
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---------------------------------------------------------------*/
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assert(step != 0);
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if (step > 0 && lo < hi)
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return 1UL + (hi - 1UL - lo) / step;
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else if (step < 0 && lo > hi)
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return 1UL + (lo - 1UL - hi) / (0UL - step);
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else
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return 0UL;
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}
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/* Return a stop value suitable for reconstructing the xrange from
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* a (start, stop, step) triple. Used in range_repr and range_reduce.
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* Computes start + len * step, clipped to the range [LONG_MIN, LONG_MAX].
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*/
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static long
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get_stop_for_range(rangeobject *r)
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{
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long last;
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if (r->len == 0)
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return r->start;
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/* The tricky bit is avoiding overflow. We first compute the last entry in
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the xrange, start + (len - 1) * step, which is guaranteed to lie within
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the range of a long, and then add step to it. See the range_reverse
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comments for an explanation of the casts below.
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*/
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last = (long)(r->start + (unsigned long)(r->len - 1) * r->step);
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if (r->step > 0)
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return last > LONG_MAX - r->step ? LONG_MAX : last + r->step;
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else
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return last < LONG_MIN - r->step ? LONG_MIN : last + r->step;
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}
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static PyObject *
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range_new(PyTypeObject *type, PyObject *args, PyObject *kw)
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{
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rangeobject *obj;
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long ilow = 0, ihigh = 0, istep = 1;
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unsigned long n;
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if (!_PyArg_NoKeywords("xrange()", kw))
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return NULL;
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if (PyTuple_Size(args) <= 1) {
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if (!PyArg_ParseTuple(args,
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"l;xrange() requires 1-3 int arguments",
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&ihigh))
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return NULL;
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}
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else {
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if (!PyArg_ParseTuple(args,
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"ll|l;xrange() requires 1-3 int arguments",
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&ilow, &ihigh, &istep))
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return NULL;
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}
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if (istep == 0) {
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PyErr_SetString(PyExc_ValueError, "xrange() arg 3 must not be zero");
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return NULL;
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}
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n = get_len_of_range(ilow, ihigh, istep);
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if (n > (unsigned long)LONG_MAX || (long)n > PY_SSIZE_T_MAX) {
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PyErr_SetString(PyExc_OverflowError,
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"xrange() result has too many items");
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return NULL;
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}
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obj = PyObject_New(rangeobject, &PyRange_Type);
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if (obj == NULL)
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return NULL;
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obj->start = ilow;
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obj->len = (long)n;
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obj->step = istep;
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return (PyObject *) obj;
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}
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PyDoc_STRVAR(range_doc,
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"xrange(stop) -> xrange object\n\
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xrange(start, stop[, step]) -> xrange object\n\
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\n\
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Like range(), but instead of returning a list, returns an object that\n\
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generates the numbers in the range on demand. For looping, this is \n\
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slightly faster than range() and more memory efficient.");
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static PyObject *
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range_item(rangeobject *r, Py_ssize_t i)
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{
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if (i < 0 || i >= r->len) {
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PyErr_SetString(PyExc_IndexError,
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"xrange object index out of range");
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return NULL;
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}
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/* do calculation entirely using unsigned longs, to avoid
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undefined behaviour due to signed overflow. */
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return PyInt_FromLong((long)(r->start + (unsigned long)i * r->step));
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}
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static Py_ssize_t
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range_length(rangeobject *r)
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{
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return (Py_ssize_t)(r->len);
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}
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static PyObject *
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range_repr(rangeobject *r)
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{
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PyObject *rtn;
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if (r->start == 0 && r->step == 1)
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rtn = PyString_FromFormat("xrange(%ld)",
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get_stop_for_range(r));
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else if (r->step == 1)
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rtn = PyString_FromFormat("xrange(%ld, %ld)",
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r->start,
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get_stop_for_range(r));
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else
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rtn = PyString_FromFormat("xrange(%ld, %ld, %ld)",
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r->start,
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get_stop_for_range(r),
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r->step);
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return rtn;
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}
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/* Pickling support */
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static PyObject *
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range_reduce(rangeobject *r, PyObject *args)
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{
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return Py_BuildValue("(O(lll))", Py_TYPE(r),
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r->start,
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get_stop_for_range(r),
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r->step);
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}
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static PySequenceMethods range_as_sequence = {
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(lenfunc)range_length, /* sq_length */
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0, /* sq_concat */
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0, /* sq_repeat */
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(ssizeargfunc)range_item, /* sq_item */
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0, /* sq_slice */
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};
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static PyObject * range_iter(PyObject *seq);
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static PyObject * range_reverse(PyObject *seq);
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PyDoc_STRVAR(reverse_doc,
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"Returns a reverse iterator.");
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static PyMethodDef range_methods[] = {
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{"__reversed__", (PyCFunction)range_reverse, METH_NOARGS, reverse_doc},
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{"__reduce__", (PyCFunction)range_reduce, METH_VARARGS},
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{NULL, NULL} /* sentinel */
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};
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PyTypeObject PyRange_Type = {
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PyObject_HEAD_INIT(&PyType_Type)
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0, /* Number of items for varobject */
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"xrange", /* Name of this type */
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sizeof(rangeobject), /* Basic object size */
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0, /* Item size for varobject */
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(destructor)PyObject_Del, /* tp_dealloc */
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0, /* tp_print */
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0, /* tp_getattr */
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0, /* tp_setattr */
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0, /* tp_compare */
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(reprfunc)range_repr, /* tp_repr */
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0, /* tp_as_number */
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&range_as_sequence, /* tp_as_sequence */
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0, /* tp_as_mapping */
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0, /* tp_hash */
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0, /* tp_call */
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0, /* tp_str */
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PyObject_GenericGetAttr, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT, /* tp_flags */
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range_doc, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */
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0, /* tp_richcompare */
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0, /* tp_weaklistoffset */
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range_iter, /* tp_iter */
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0, /* tp_iternext */
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range_methods, /* tp_methods */
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0, /* tp_members */
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0, /* tp_getset */
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0, /* tp_base */
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0, /* tp_dict */
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0, /* tp_descr_get */
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0, /* tp_descr_set */
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0, /* tp_dictoffset */
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0, /* tp_init */
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0, /* tp_alloc */
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range_new, /* tp_new */
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};
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/*********************** Xrange Iterator **************************/
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typedef struct {
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PyObject_HEAD
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long index;
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long start;
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long step;
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long len;
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} rangeiterobject;
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static PyObject *
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rangeiter_next(rangeiterobject *r)
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{
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if (r->index < r->len)
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return PyInt_FromLong(r->start + (r->index++) * r->step);
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return NULL;
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}
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static PyObject *
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rangeiter_len(rangeiterobject *r)
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{
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return PyInt_FromLong(r->len - r->index);
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}
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PyDoc_STRVAR(length_hint_doc, "Private method returning an estimate of len(list(it)).");
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static PyMethodDef rangeiter_methods[] = {
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{"__length_hint__", (PyCFunction)rangeiter_len, METH_NOARGS, length_hint_doc},
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{NULL, NULL} /* sentinel */
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};
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static PyTypeObject Pyrangeiter_Type = {
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PyObject_HEAD_INIT(&PyType_Type)
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0, /* ob_size */
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"rangeiterator", /* tp_name */
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sizeof(rangeiterobject), /* tp_basicsize */
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0, /* tp_itemsize */
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/* methods */
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(destructor)PyObject_Del, /* tp_dealloc */
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0, /* tp_print */
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0, /* tp_getattr */
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0, /* tp_setattr */
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0, /* tp_compare */
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0, /* tp_repr */
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0, /* tp_as_number */
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0, /* tp_as_sequence */
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0, /* tp_as_mapping */
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0, /* tp_hash */
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0, /* tp_call */
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0, /* tp_str */
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PyObject_GenericGetAttr, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT, /* tp_flags */
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0, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */
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0, /* tp_richcompare */
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0, /* tp_weaklistoffset */
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PyObject_SelfIter, /* tp_iter */
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(iternextfunc)rangeiter_next, /* tp_iternext */
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rangeiter_methods, /* tp_methods */
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0,
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};
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static PyObject *
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range_iter(PyObject *seq)
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{
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rangeiterobject *it;
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if (!PyRange_Check(seq)) {
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PyErr_BadInternalCall();
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return NULL;
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}
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it = PyObject_New(rangeiterobject, &Pyrangeiter_Type);
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if (it == NULL)
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return NULL;
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it->index = 0;
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it->start = ((rangeobject *)seq)->start;
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it->step = ((rangeobject *)seq)->step;
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it->len = ((rangeobject *)seq)->len;
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return (PyObject *)it;
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}
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static PyObject *
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range_reverse(PyObject *seq)
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{
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rangeiterobject *it;
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long start, step, len;
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if (!PyRange_Check(seq)) {
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PyErr_BadInternalCall();
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return NULL;
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}
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it = PyObject_New(rangeiterobject, &Pyrangeiter_Type);
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if (it == NULL)
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return NULL;
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start = ((rangeobject *)seq)->start;
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step = ((rangeobject *)seq)->step;
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len = ((rangeobject *)seq)->len;
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it->index = 0;
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it->len = len;
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/* the casts below guard against signed overflow by turning it
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into unsigned overflow instead. The correctness of this
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code still depends on conversion from unsigned long to long
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wrapping modulo ULONG_MAX+1, which isn't guaranteed (see
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C99 6.3.1.3p3) but seems to hold in practice for all
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platforms we're likely to meet.
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If step == LONG_MIN then we still end up with LONG_MIN
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after negation; but this works out, since we've still got
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the correct value modulo ULONG_MAX+1, and the range_item
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calculation is also done modulo ULONG_MAX+1.
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*/
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it->start = (long)(start + (unsigned long)(len-1) * step);
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it->step = (long)(0UL-step);
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return (PyObject *)it;
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}
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