diff options
Diffstat (limited to 'Objects/longobject.c')
| -rw-r--r-- | Objects/longobject.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/Objects/longobject.c b/Objects/longobject.c index d88a13e..fa0142f 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -160,6 +160,7 @@ PyObject * PyLong_FromLong(long ival) { PyLongObject *v; + unsigned long abs_ival; unsigned long t; /* unsigned so >> doesn't propagate sign bit */ int ndigits = 0; int sign = 1; @@ -167,9 +168,15 @@ PyLong_FromLong(long ival) CHECK_SMALL_INT(ival); if (ival < 0) { - ival = -ival; + /* if LONG_MIN == -LONG_MAX-1 (true on most platforms) then + ANSI C says that the result of -ival is undefined when ival + == LONG_MIN. Hence the following workaround. */ + abs_ival = (unsigned long)(-1-ival) + 1; sign = -1; } + else { + abs_ival = (unsigned long)ival; + } /* Fast path for single-digits ints */ if (!(ival>>PyLong_SHIFT)) { @@ -193,7 +200,7 @@ PyLong_FromLong(long ival) } /* Larger numbers: loop to determine number of digits */ - t = (unsigned long)ival; + t = abs_ival; while (t) { ++ndigits; t >>= PyLong_SHIFT; @@ -202,7 +209,7 @@ PyLong_FromLong(long ival) if (v != NULL) { digit *p = v->ob_digit; Py_SIZE(v) = ndigits*sign; - t = (unsigned long)ival; + t = abs_ival; while (t) { *p++ = (digit)(t & PyLong_MASK); t >>= PyLong_SHIFT; @@ -1033,21 +1040,27 @@ PyObject * PyLong_FromLongLong(PY_LONG_LONG ival) { PyLongObject *v; + unsigned PY_LONG_LONG abs_ival; unsigned PY_LONG_LONG t; /* unsigned so >> doesn't propagate sign bit */ int ndigits = 0; int negative = 0; CHECK_SMALL_INT(ival); if (ival < 0) { - ival = -ival; + /* avoid signed overflow on negation; see comments + in PyLong_FromLong above. */ + abs_ival = (unsigned PY_LONG_LONG)(-1-ival) + 1; negative = 1; } + else { + abs_ival = (unsigned PY_LONG_LONG)ival; + } /* Count the number of Python digits. We used to pick 5 ("big enough for anything"), but that's a waste of time and space given that 5*15 = 75 bits are rarely needed. */ - t = (unsigned PY_LONG_LONG)ival; + t = abs_ival; while (t) { ++ndigits; t >>= PyLong_SHIFT; @@ -1056,7 +1069,7 @@ PyLong_FromLongLong(PY_LONG_LONG ival) if (v != NULL) { digit *p = v->ob_digit; Py_SIZE(v) = negative ? -ndigits : ndigits; - t = (unsigned PY_LONG_LONG)ival; + t = abs_ival; while (t) { *p++ = (digit)(t & PyLong_MASK); t >>= PyLong_SHIFT; |