[src/trunk]: src/usr.bin/xlint/lint1 Fix a bug in detecting overflow in unsig...

[perry <perry%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/979e6d041205
branches:  trunk
changeset: 517690:979e6d041205
user:      perry <perry%NetBSD.org@localhost>
date:      Sat Nov 17 04:35:32 2001 +0000

description:
Fix a bug in detecting overflow in unsigned multiplication.

XXX Note that the overflow code for many cases seems to be buggy. I've
only fixed one bug that was bothering me. A set of regression tests
and extensive testing are needed.

diffstat:

 usr.bin/xlint/lint1/tree.c |  29 +++++++++++++++++++++--------
 1 files changed, 21 insertions(+), 8 deletions(-)

diffs (78 lines):

diff -r 14cddaa69044 -r 979e6d041205 usr.bin/xlint/lint1/tree.c
--- a/usr.bin/xlint/lint1/tree.c        Sat Nov 17 03:54:36 2001 +0000
+++ b/usr.bin/xlint/lint1/tree.c        Sat Nov 17 04:35:32 2001 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tree.c,v 1.21 2001/09/16 16:34:44 wiz Exp $    */
+/*     $NetBSD: tree.c,v 1.22 2001/11/17 04:35:32 perry Exp $  */
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -33,7 +33,7 @@
 
 #include <sys/cdefs.h>
 #ifndef lint
-__RCSID("$NetBSD: tree.c,v 1.21 2001/09/16 16:34:44 wiz Exp $");
+__RCSID("$NetBSD: tree.c,v 1.22 2001/11/17 04:35:32 perry Exp $");
 #endif
 
 #include <stdlib.h>
@@ -2608,6 +2608,12 @@
 }
 
 /*
+ * XXX
+ * Note: There appear to be a number of bugs in detecting overflow in
+ * this function. An audit and a set of proper regression tests are needed.
+ *     --Perry Metzger, Nov. 16, 2001
+ */
+/*
  * Do only as much as necessary to compute constant expressions.
  * Called only if the operator allows folding and (both) operands
  * are constants.
@@ -2630,6 +2636,7 @@
        if (modtab[tn->tn_op].m_binary)
                ur = sr = tn->tn_right->tn_val->v_quad;
 
+       mask = qlmasks[size(t)];
        ovfl = 0;
 
        switch (tn->tn_op) {
@@ -2645,9 +2652,17 @@
                q = ~sl;
                break;
        case MULT:
-               q = utyp ? ul * ur : sl * sr;
-               if (msb(q, t, -1) != (msb(sl, t, -1) ^ msb(sr, t, -1)))
-                       ovfl = 1;
+               if (utyp) {
+                       q = ul * ur;
+                       if (q != (q & mask))
+                               ovfl = 1;
+                       else if ((ul != 0) && ((q / ul) != ur))
+                               ovfl = 1;
+               } else {
+                       q = sl * sr;
+                       if (msb(q, t, -1) != (msb(sl, t, -1) ^ msb(sr, t, -1)))
+                               ovfl = 1;
+               }
                break;
        case DIV:
                if (sr == 0) {
@@ -2692,7 +2707,7 @@
                break;
        case SHR:
                /*
-                * The sign must be explizitly extended because
+                * The sign must be explicitly extended because
                 * shifts of signed values are implementation dependent.
                 */
                q = ul >> sr;
@@ -2729,8 +2744,6 @@
                lerror("fold() 5");
        }
 
-       mask = qlmasks[size(t)];
-
        /* XXX does not work for quads. */
        if (ovfl || ((q | mask) != ~(u_quad_t)0 && (q & ~mask) != 0)) {
                if (hflag)