diff options
Diffstat (limited to 'Objects/longobject.c')
| -rw-r--r-- | Objects/longobject.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Objects/longobject.c b/Objects/longobject.c index 1c127baccd..7f09bb66ba 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -2197,10 +2197,18 @@ long_hash(PyLongObject *v) i = -(i); } #define LONG_BIT_PyLong_SHIFT (8*sizeof(long) - PyLong_SHIFT) + /* The following loop produces a C long x such that (unsigned long)x + is congruent to the absolute value of v modulo ULONG_MAX. The + resulting x is nonzero if and only if v is. */ while (--i >= 0) { /* Force a native long #-bits (32 or 64) circular shift */ x = ((x << PyLong_SHIFT) & ~PyLong_MASK) | ((x >> LONG_BIT_PyLong_SHIFT) & PyLong_MASK); x += v->ob_digit[i]; + /* If the addition above overflowed (thinking of x as + unsigned), we compensate by incrementing. This preserves + the value modulo ULONG_MAX. */ + if ((unsigned long)x < v->ob_digit[i]) + x++; } #undef LONG_BIT_PyLong_SHIFT x = x * sign; |