I observed gcc 2.95.4 and gcc 3.1 interpret (or maybe optimize) the
following code differently (CFLAGS=-O):
int main(void)
{
unsigned char i = 127;
printf("%d\n", ((char)(i << 1)) / 2);
return 0;
}
gcc 2.95.4 says it's -1, whereas gcc 3.1 says it's 127. On FreeBSD
char should be signed, so I suspect it's a (optimization) bug of gcc
3.1 which should be fixed. Or we'll have to do a mass audit of the
whole src tree to check and fix the similar expressions.
In any case, this behavior makes moused(8) return a stupid value of
127 when you roll the mouse wheel up under ps/2-sysmouse-intellimouse
protocol. Attached is a patch that makes the whole expression look
more logical and works around the above behavior at the same time.
--
/
/__ __ Akinori.org / MUSHA.org
/ ) ) ) ) / FreeBSD.org / Ruby-lang.org
Akinori MUSHA aka / (_ / ( (__( @ iDaemons.org / and.or.jp
"Somewhere out of a memory.. of lighted streets on quiet nights.."
Index: moused.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/moused/moused.c,v
retrieving revision 1.55
diff -u -r1.55 moused.c
--- moused.c 28 Apr 2002 11:59:30 -0000 1.55
+++ moused.c 15 May 2002 17:16:40 -0000
@@ -1972,7 +1972,7 @@
act->dx = (char)(pBuf[1]) + (char)(pBuf[3]);
act->dy = - ((char)(pBuf[2]) + (char)(pBuf[4]));
if (rodent.level == 1) {
- act->dz = ((char)(pBuf[5] << 1) + (char)(pBuf[6] << 1))/2;
+ act->dz = ((char)(pBuf[5] << 1) + (char)(pBuf[6] << 1)) >> 1;
act->button |= ((~pBuf[7] & MOUSE_SYS_EXTBUTTONS) << 3);
}
break;
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