The tail end of x_sub implicitly assumed that an unsigned short

tim-one · tim-one · commit 43f04a36cf4e · 2000-07-08T02:26:47.000Z
contains 16 bits.  Not true on Cray J90.
diff --git a/Objects/longobject.c b/Objects/longobject.c
@@ -1048,6 +1048,7 @@ x_sub(PyLongObject *a, PyLongObject *b)
 		borrow = a->ob_digit[i] - borrow;
 		z->ob_digit[i] = borrow & MASK;
 		borrow >>= SHIFT;
+		borrow &= 1; /* Keep only one sign bit */
 	}
 	assert(borrow == 0);
 	if (sign < 0)

Original file line number	Diff line number	Diff line change
`@@ -1048,6 +1048,7 @@ x_sub(PyLongObject a, PyLongObject b)`
`1048`	`1048`	`borrow = a->ob_digit[i] - borrow;`
`1049`	`1049`	`z->ob_digit[i] = borrow & MASK;`
`1050`	`1050`	`borrow >>= SHIFT;`
	`1051`	`+ borrow &= 1; /* Keep only one sign bit */`
`1051`	`1052`	`}`
`1052`	`1053`	`assert(borrow == 0);`
`1053`	`1054`	`if (sign < 0)`