diff options
Diffstat (limited to 'Objects/intobject.c')
| -rw-r--r-- | Objects/intobject.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/Objects/intobject.c b/Objects/intobject.c index 4e1f04f242..a4d50be129 100644 --- a/Objects/intobject.c +++ b/Objects/intobject.c @@ -546,6 +546,17 @@ int_mul(PyObject *v, PyObject *w) } } +/* Integer overflow checking for unary negation: on a 2's-complement + * box, -x overflows iff x is the most negative long. In this case we + * get -x == x. However, -x is undefined (by C) if x /is/ the most + * negative long (it's a signed overflow case), and some compilers care. + * So we cast x to unsigned long first. However, then other compilers + * warn about applying unary minus to an unsigned operand. Hence the + * weird "0-". + */ +#define UNARY_NEG_WOULD_OVERFLOW(x) \ + ((x) < 0 && (unsigned long)(x) == 0-(unsigned long)(x)) + /* Return type of i_divmod */ enum divmod_result { DIVMOD_OK, /* Correct result */ @@ -565,7 +576,7 @@ i_divmod(register long x, register long y, return DIVMOD_ERROR; } /* (-sys.maxint-1)/-1 is the only overflow case. */ - if (y == -1 && x == LONG_MIN) + if (y == -1 && UNARY_NEG_WOULD_OVERFLOW(x)) return DIVMOD_OVERFLOW; xdivy = x / y; xmody = x - xdivy * y; @@ -756,7 +767,8 @@ int_neg(PyIntObject *v) { register long a; a = v->ob_ival; - if (a < 0 && (unsigned long)a == 0-(unsigned long)a) { + /* check for overflow */ + if (UNARY_NEG_WOULD_OVERFLOW(a)) { PyObject *o = PyLong_FromLong(a); if (o != NULL) { PyObject *result = PyNumber_Negative(o); |