bpo-31619: Fixed a ValueError when convert a string with large number of underscores (#3827)

to integer with binary base.

1 files changed, 4 insertions, 4 deletions

diff --git a/Objects/longobject.c b/Objects/longobject.c
index 3b07585..c71b783 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -2057,15 +2057,15 @@ long_from_binary_base(const char **str, int base, PyLongObject **res)
     }
 
     *str = p;
-    /* n <- # of Python digits needed, = ceiling(n/PyLong_SHIFT). */
-    n = digits * bits_per_char + PyLong_SHIFT - 1;
-    if (n / bits_per_char < p - start) {
+    /* n <- the number of Python digits needed,
+            = ceiling((digits * bits_per_char) / PyLong_SHIFT). */
+    if (digits > (PY_SSIZE_T_MAX - (PyLong_SHIFT - 1)) / bits_per_char) {
         PyErr_SetString(PyExc_ValueError,
                         "int string too large to convert");
         *res = NULL;
         return 0;
     }
-    n = n / PyLong_SHIFT;
+    n = (digits * bits_per_char + PyLong_SHIFT - 1) / PyLong_SHIFT;
     z = _PyLong_New(n);
     if (z == NULL) {
         *res = NULL;