mp_bytecode_print_str: avoid undefined behavior

Left shift of negative numbers is undefined in the "C" standard.  Multiplying
by 128 has the intended effect (in the absence of integer overflow, anyway),
can be implemented using the same shift instruction, but does not invoke
undefined behavior.

This problem was found using clang 7's scan-build static analyzer.

1 files changed, 1 insertions, 1 deletions

diff --git a/py/showbc.c b/py/showbc.c
index 3deb18cd3..e71d8a253 100644
--- a/py/showbc.c
+++ b/py/showbc.c
@@ -185,7 +185,7 @@ const byte *mp_bytecode_print_str(const byte *ip) {
                 num--;
             }
             do {
-                num = (num << 7) | (*ip & 0x7f);
+                num = (num * 128) | (*ip & 0x7f);
             } while ((*ip++ & 0x80) != 0);
             printf("LOAD_CONST_SMALL_INT " INT_FMT, num);
             break;