bpo-30281: Fix the default value for stop in PySlice_Unpack() (#1480) (#1529)

zhangyangyu · web-flow · commit 98b49a00d413 · 2017-05-10T19:00:15.000+08:00
diff --git a/Objects/sliceobject.c b/Objects/sliceobject.c
@@ -197,6 +197,8 @@ PySlice_Unpack(PyObject *_r,
     PySliceObject *r = (PySliceObject*)_r;
     /* this is harder to get right than you might think */
 
+    Py_BUILD_ASSERT(PY_SSIZE_T_MIN + 1 <= -PY_SSIZE_T_MAX);
+
     if (r->step == Py_None) {
         *step = 1;
     }
@@ -217,14 +219,14 @@ PySlice_Unpack(PyObject *_r,
     }
 
     if (r->start == Py_None) {
-        *start = *step < 0 ? PY_SSIZE_T_MAX-1 : 0;;
+        *start = *step < 0 ? PY_SSIZE_T_MAX : 0;
     }
     else {
         if (!_PyEval_SliceIndex(r->start, start)) return -1;
     }
 
     if (r->stop == Py_None) {
-        *stop = *step < 0 ? -PY_SSIZE_T_MAX : PY_SSIZE_T_MAX;
+        *stop = *step < 0 ? PY_SSIZE_T_MIN : PY_SSIZE_T_MAX;
     }
     else {
         if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
@@ -258,7 +260,7 @@ PySlice_AdjustIndices(Py_ssize_t length,
             *stop = (step < 0) ? -1 : 0;
         }
     }
-    else  if (*stop >= length) {
+    else if (*stop >= length) {
         *stop = (step < 0) ? length - 1 : length;
     }
 
diff --git a/Python/ceval.c b/Python/ceval.c
@@ -5071,7 +5071,7 @@ do_call_core(PyObject *func, PyObject *callargs, PyObject *kwdict)
 /* Extract a slice index from a PyLong or an object with the
    nb_index slot defined, and store in *pi.
    Silently reduce values larger than PY_SSIZE_T_MAX to PY_SSIZE_T_MAX,
-   and silently boost values less than -PY_SSIZE_T_MAX-1 to -PY_SSIZE_T_MAX-1.
+   and silently boost values less than PY_SSIZE_T_MIN to PY_SSIZE_T_MIN.
    Return 0 on error, 1 on success.
 */
 int

Original file line number	Diff line number	Diff line change
`@@ -197,6 +197,8 @@ PySlice_Unpack(PyObject *_r,`
`197`	`197`	`PySliceObject r = (PySliceObject)_r;`
`198`	`198`	`/* this is harder to get right than you might think */`
`199`	`199`
	`200`	`+ Py_BUILD_ASSERT(PY_SSIZE_T_MIN + 1 <= -PY_SSIZE_T_MAX);`
	`201`	`+`
`200`	`202`	`if (r->step == Py_None) {`
`201`	`203`	`*step = 1;`
`202`	`204`	`}`
`@@ -217,14 +219,14 @@ PySlice_Unpack(PyObject *_r,`
`217`	`219`	`}`
`218`	`220`
`219`	`221`	`if (r->start == Py_None) {`
`220`		`- start = step < 0 ? PY_SSIZE_T_MAX-1 : 0;;`
	`222`	`+ start = step < 0 ? PY_SSIZE_T_MAX : 0;`
`221`	`223`	`}`
`222`	`224`	`else {`
`223`	`225`	`if (!_PyEval_SliceIndex(r->start, start)) return -1;`
`224`	`226`	`}`
`225`	`227`
`226`	`228`	`if (r->stop == Py_None) {`
`227`		`- stop = step < 0 ? -PY_SSIZE_T_MAX : PY_SSIZE_T_MAX;`
	`229`	`+ stop = step < 0 ? PY_SSIZE_T_MIN : PY_SSIZE_T_MAX;`
`228`	`230`	`}`
`229`	`231`	`else {`
`230`	`232`	`if (!_PyEval_SliceIndex(r->stop, stop)) return -1;`
`@@ -258,7 +260,7 @@ PySlice_AdjustIndices(Py_ssize_t length,`
`258`	`260`	`*stop = (step < 0) ? -1 : 0;`
`259`	`261`	`}`
`260`	`262`	`}`
`261`		`- else if (*stop >= length) {`
	`263`	`+ else if (*stop >= length) {`
`262`	`264`	`*stop = (step < 0) ? length - 1 : length;`
`263`	`265`	`}`
`264`	`266`