diff options
Diffstat (limited to 'Objects/rangeobject.c')
| -rw-r--r-- | Objects/rangeobject.c | 86 |
1 files changed, 84 insertions, 2 deletions
diff --git a/Objects/rangeobject.c b/Objects/rangeobject.c index 002f94a..0ac4687 100644 --- a/Objects/rangeobject.c +++ b/Objects/rangeobject.c @@ -47,6 +47,76 @@ PyRange_New(long start, long len, long step, int reps) return (PyObject *) obj; } +/* 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) +{ + long ilow = 0, ihigh = 0, istep = 1; + long n; + + 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; + } + return PyRange_New(ilow, n, istep, 1); +} + +static char 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. This is slightly slower\n\ +than range() but more memory efficient."; + static PyObject * range_item(rangeobject *r, int i) { @@ -118,12 +188,24 @@ PyTypeObject PyRange_Type = { 0, /* tp_setattro */ 0, /* tp_as_buffer */ Py_TPFLAGS_DEFAULT, /* tp_flags */ - 0, /* tp_doc */ + range_doc, /* tp_doc */ 0, /* tp_traverse */ 0, /* tp_clear */ 0, /* tp_richcompare */ 0, /* tp_weaklistoffset */ - (getiterfunc)range_iter, /* tp_iter */ + (getiterfunc)range_iter, /* tp_iter */ + 0, /* tp_iternext */ + 0, /* 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 **************************/ |