py/objint_longlong: Add arithmetic overflow checks.

Long long big integer support now raises an exception on overflow rather
than returning an undefined result.

Also adds an error when shifting by a negative value.

The new arithmetic checks are added in the misc.h header.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

1 files changed, 12 insertions, 1 deletions

diff --git a/tests/basics/int_64_basics.py b/tests/basics/int_64_basics.py
index 73a06b64b..289ea49b6 100644
--- a/tests/basics/int_64_basics.py
+++ b/tests/basics/int_64_basics.py
@@ -117,10 +117,21 @@ x = -4611686018427387904 # big
 # sys.maxsize is a constant bigint, so test it's compatible with dynamic ones
 import sys
 if hasattr(sys, "maxsize"):
-    print(sys.maxsize + 1 - 1 == sys.maxsize)
+    print(sys.maxsize - 1 + 1 == sys.maxsize)
 else:
     print(True)  # No maxsize property in this config
 
 # test extraction of big int value via mp_obj_get_int_maybe
 x = 1 << 62
 print('a' * (x + 4 - x))
+
+# negative shifts are invalid
+try:
+    print((1 << 48) >> -4)
+except ValueError as e:
+    print(e)
+
+try:
+    print((1 << 48) << -6)
+except ValueError as e:
+    print(e)