py: change negative array indices with array - 1.
diff --git a/py/vm.c b/py/vm.c
index f3c38b8..c549e2b 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -78,7 +78,7 @@
volatile machine_uint_t currently_in_except_block = 0; // 0 or 1, to detect nested exceptions
machine_uint_t exc_stack[8]; // on the exception stack we store (ip, sp | X) for each block, X = previous value of currently_in_except_block
- machine_uint_t *volatile exc_sp = &exc_stack[-1]; // stack grows up, exc_sp points to top of stack
+ machine_uint_t *volatile exc_sp = &exc_stack[0] - 1; // stack grows up, exc_sp points to top of stack
// outer exception handling loop
for (;;) {
@@ -453,7 +453,7 @@
case MP_BC_RETURN_VALUE:
nlr_pop();
*sp_in_out = sp;
- assert(exc_sp == &exc_stack[-1]);
+ assert(exc_sp == &exc_stack[0] - 1);
return false;
case MP_BC_YIELD_VALUE: