Change long/long true division to return as many good bits as it can;

e.g., (1L << 40000)/(1L << 40001) returns 0.5, not Inf or NaN or whatever.

3 files changed, 78 insertions, 2 deletions

diff --git a/Lib/test/test_long_future.py b/Lib/test/test_long_future.py
new file mode 100644
index 0000000..4348bbe
--- /dev/null
+++ b/Lib/test/test_long_future.py
@@ -0,0 +1,38 @@
+from __future__ import division
+# When true division is the default, get rid of this and add it to
+# test_long.py instead.  In the meantime, it's too obscure to try to
+# trick just part of test_long into using future division.
+
+from test_support import TestFailed, verify, verbose
+
+def test_true_division():
+    if verbose:
+        print "long true division"
+    huge = 1L << 40000
+    mhuge = -huge
+    verify(huge / huge == 1.0)
+    verify(mhuge / mhuge == 1.0)
+    verify(huge / mhuge == -1.0)
+    verify(mhuge / huge == -1.0)
+    verify(1 / huge == 0.0)
+    verify(1L / huge == 0.0)
+    verify(1 / mhuge == 0.0)
+    verify(1L / mhuge ==- 0.0)
+    verify((666 * huge + (huge >> 1)) / huge == 666.5)
+    verify((666 * mhuge + (mhuge >> 1)) / mhuge == 666.5)
+    verify((666 * huge + (huge >> 1)) / mhuge == -666.5)
+    verify((666 * mhuge + (mhuge >> 1)) / huge == -666.5)
+    verify(huge / (huge << 1) == 0.5)
+
+    namespace = {'huge': huge, 'mhuge': mhuge}
+    for overflow in ["float(huge)", "float(mhuge)",
+                     "huge / 1", "huge / 2L", "huge / -1", "huge / -2L",
+                     "mhuge / 100", "mhuge / 100L"]:
+        try:
+            eval(overflow, namespace)
+        except OverflowError:
+            pass
+        else:
+            raise TestFailed("expected OverflowError from %r" % overflow)
+
+test_true_division()
diff --git a/Objects/intobject.c b/Objects/intobject.c
index 775213c..73d5e77 100644
--- a/Objects/intobject.c
+++ b/Objects/intobject.c
@@ -535,7 +535,14 @@ int_classic_div(PyIntObject *x, PyIntObject *y)
 static PyObject *
 int_true_divide(PyObject *v, PyObject *w)
 {
-	return PyFloat_Type.tp_as_number->nb_true_divide(v, w);
+	/* If they aren't both ints, give someone else a chance.  In
+	   particular, this lets int/long get handled by longs, which
+	   underflows to 0 gracefully if the long is too big to convert
+	   to float. */
+	if (PyInt_Check(v) && PyInt_Check(w))
+		return PyFloat_Type.tp_as_number->nb_true_divide(v, w);
+	Py_INCREF(Py_NotImplemented);
+	return Py_NotImplemented;
 }
 
 static PyObject *
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 7aa6005..5da5113 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -1584,7 +1584,38 @@ long_classic_div(PyObject *v, PyObject *w)
 static PyObject *
 long_true_divide(PyObject *v, PyObject *w)
 {
-	return PyFloat_Type.tp_as_number->nb_divide(v, w);
+	PyLongObject *a, *b;
+	double ad, bd;
+	int aexp, bexp;
+
+	CONVERT_BINOP(v, w, &a, &b);
+	ad = _PyLong_AsScaledDouble((PyObject *)a, &aexp);
+	bd = _PyLong_AsScaledDouble((PyObject *)b, &bexp);
+	if ((ad == -1.0 || bd == -1.0) && PyErr_Occurred())
+		return NULL;
+
+	if (bd == 0.0) {
+		PyErr_SetString(PyExc_ZeroDivisionError,
+			"long division or modulo by zero");
+		return NULL;
+	}
+
+	/* True value is very close to ad/bd * 2**(SHIFT*(aexp-bexp)) */
+	ad /= bd;	/* overflow/underflow impossible here */
+	aexp -= bexp;
+	if (aexp > INT_MAX / SHIFT)
+		goto overflow;
+	errno = 0;
+	ad = ldexp(ad, aexp * SHIFT);
+	if (ad != 0 && errno == ERANGE) /* ignore underflow to 0.0 */
+		goto overflow;
+	return PyFloat_FromDouble(ad);
+
+overflow:
+	PyErr_SetString(PyExc_OverflowError,
+		"long/long too large for a float");
+	return NULL;
+	
 }
 
 static PyObject *