py: Raise a ValueError if range() step is zero.

dpgeorge · dpgeorge · commit de9b53695d1b · 2017-04-05T10:50:26.000+10:00
Following CPython.  Otherwise one gets either an infinite loop (if code is
optimised by the uPy compiler) or possibly a divide-by-zero CPU exception.
diff --git a/py/compile.c b/py/compile.c
@@ -1444,8 +1444,9 @@ STATIC void compile_for_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
                     pn_range_start = args[0];
                     pn_range_end = args[1];
                     pn_range_step = args[2];
-                    // We need to know sign of step. This is possible only if it's constant
-                    if (!MP_PARSE_NODE_IS_SMALL_INT(pn_range_step)) {
+                    // the step must be a non-zero constant integer to do the optimisation
+                    if (!MP_PARSE_NODE_IS_SMALL_INT(pn_range_step)
+                        || MP_PARSE_NODE_LEAF_SMALL_INT(pn_range_step) == 0) {
                         optimize = false;
                     }
                 }
diff --git a/py/objrange.c b/py/objrange.c
@@ -105,8 +105,10 @@ STATIC mp_obj_t range_make_new(const mp_obj_type_t *type, size_t n_args, size_t
         o->start = mp_obj_get_int(args[0]);
         o->stop = mp_obj_get_int(args[1]);
         if (n_args == 3) {
-            // TODO check step is non-zero
             o->step = mp_obj_get_int(args[2]);
+            if (o->step == 0) {
+                mp_raise_ValueError("zero step");
+            }
         }
     }
 

Original file line number	Diff line number	Diff line change
`@@ -1444,8 +1444,9 @@ STATIC void compile_for_stmt(compiler_t comp, mp_parse_node_struct_t pns) {`
`1444`	`1444`	`pn_range_start = args[0];`
`1445`	`1445`	`pn_range_end = args[1];`
`1446`	`1446`	`pn_range_step = args[2];`
`1447`		`- // We need to know sign of step. This is possible only if it's constant`
`1448`		`- if (!MP_PARSE_NODE_IS_SMALL_INT(pn_range_step)) {`
	`1447`	`+ // the step must be a non-zero constant integer to do the optimisation`
	`1448`	`+ if (!MP_PARSE_NODE_IS_SMALL_INT(pn_range_step)`
	`1449`	`+ \|\| MP_PARSE_NODE_LEAF_SMALL_INT(pn_range_step) == 0) {`
`1449`	`1450`	`optimize = false;`
`1450`	`1451`	`}`
`1451`	`1452`	`}`
Original file line number	Diff line number	Diff line change
`@@ -105,8 +105,10 @@ STATIC mp_obj_t range_make_new(const mp_obj_type_t *type, size_t n_args, size_t`
`105`	`105`	`o->start = mp_obj_get_int(args[0]);`
`106`	`106`	`o->stop = mp_obj_get_int(args[1]);`
`107`	`107`	`if (n_args == 3) {`
`108`		`- // TODO check step is non-zero`
`109`	`108`	`o->step = mp_obj_get_int(args[2]);`
	`109`	`+ if (o->step == 0) {`
	`110`	`+ mp_raise_ValueError("zero step");`
	`111`	`+ }`
`110`	`112`	`}`
`111`	`113`	`}`
`112`	`114`