Merged revisions 68974-68975 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r68974 | mark.dickinson | 2009-01-26 21:36:30 +0000 (Mon, 26 Jan 2009) | 4 lines

  Fix undefined behaviour (left shift of negative value) in long_hash.  Also,
  rewrap a line of length > 79, and update comments.
........
  r68975 | mark.dickinson | 2009-01-26 21:40:08 +0000 (Mon, 26 Jan 2009) | 2 lines

  Fix comment.
........

diff --git a/Objects/longobject.c b/Objects/longobject.c
index 0493dbc3e717d938e71d507910fd80f9183dea2e..76986fd4ee1f58ef4fc5cd0f105afd49952ab3d9 100644 (file)
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -2274,7 +2274,7 @@ long_richcompare(PyObject *self, PyObject *other, int op)
 static long
 long_hash(PyLongObject *v)
 {
-       long x;
+       unsigned long x;
        Py_ssize_t i;
        int sign;
 
@@ -2294,17 +2294,18 @@ 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
+       /* The following loop produces a C unsigned long x such that 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 = ((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])
+               /* If the addition above overflowed we compensate by
+                  incrementing.  This preserves the value modulo
+                  ULONG_MAX. */
+               if (x < v->ob_digit[i])
                        x++;
        }
 #undef LONG_BIT_PyLong_SHIFT