add _PyEval_UnpackIndices

Author: cocolato

Include/cpython/ceval.h

@@ -23,6 +23,9 @@ _PyEval_RequestCodeExtraIndex(freefunc f) {
 
 PyAPI_FUNC(int) _PyEval_SliceIndex(PyObject *, Py_ssize_t *);
 PyAPI_FUNC(int) _PyEval_SliceIndexNotNone(PyObject *, Py_ssize_t *);
+PyAPI_FUNC(int) _PyEval_UnpackIndices(PyObject *, PyObject *,
+                                      Py_ssize_t,
+                                      Py_ssize_t *, Py_ssize_t *);
 
 
 // Trampoline API

Modules/_testinternalcapi/test_cases.c.h

@@ -878,22 +878,20 @@ dummy_func(
                 Py_ssize_t len = PyUnicode_CheckExact(container_o)
                     ? PyUnicode_GET_LENGTH(container_o)
                     : Py_SIZE(container_o);
-                Py_ssize_t istart = 0, istop = PY_SSIZE_T_MAX;
-                if (!_PyEval_SliceIndex(start_o, &istart) ||
-                    !_PyEval_SliceIndex(stop_o, &istop)) {
+                Py_ssize_t istart, istop;
+                int err = _PyEval_UnpackIndices(start_o, stop_o, len,
+                                                      &istart, &istop);
+                if (err == 0) {
                     res_o = NULL;
                 }
+                else if (PyList_CheckExact(container_o)) {
+                    res_o = PyList_GetSlice(container_o, istart, istop);
+                }
+                else if (PyTuple_CheckExact(container_o)) {
+                    res_o = PyTuple_GetSlice(container_o, istart, istop);
+                }
                 else {
-                    PySlice_AdjustIndices(len, &istart, &istop, 1);
-                    if (PyList_CheckExact(container_o)) {
-                        res_o = PyList_GetSlice(container_o, istart, istop);
-                    }
-                    else if (PyTuple_CheckExact(container_o)) {
-                        res_o = PyTuple_GetSlice(container_o, istart, istop);
-                    }
-                    else {
-                        res_o = PyUnicode_Substring(container_o, istart, istop);
-                    }
+                    res_o = PyUnicode_Substring(container_o, istart, istop);
                 }
             }
             else {

Python/bytecodes.c

@@ -2922,6 +2922,26 @@ _PyEval_SliceIndexNotNone(PyObject *v, Py_ssize_t *pi)
     return 1;
 }
 
+int
+_PyEval_UnpackIndices(PyObject *start, PyObject *stop,
+                      Py_ssize_t len,
+                      Py_ssize_t *istart, Py_ssize_t *istop)
+{
+    if (len < 0) {
+        return 0;
+    }
+    *istart = 0;
+    *istop = PY_SSIZE_T_MAX;
+    if (!_PyEval_SliceIndex(start, istart)) {
+        return 0;
+    }
+    if (!_PyEval_SliceIndex(stop, istop)) {
+        return 0;
+    }
+    PySlice_AdjustIndices(len, istart, istop, 1);
+    return 1;
+}
+
 PyObject *
 _PyEval_ImportName(PyThreadState *tstate, PyObject *builtins,
             PyObject *globals, PyObject *locals, PyObject *name,