Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!rutgers!husc6!seismo!munnari!vuwcomp!newbery
From: newbery@vuwcomp.UUCP
Newsgroups: comp.sys.mac
Subject: Code generation bug in MPW Pascal
Message-ID: <12620@vuwcomp.UUCP>
Date: Sun, 8-Feb-87 23:37:12 EST
Article-I.D.: vuwcomp.12620
Posted: Sun Feb  8 23:37:12 1987
Date-Received: Wed, 11-Feb-87 07:34:35 EST
Organization: Comp Sci, Victoria Univ., Wellington, New Zealand
Lines: 36
Keywords: MPW, Pascal


MPW Pascal can generate bad code when widening a signedByte to a char. Consider
the following code fragment.
----------------------------------------------------------------------
VAR
	p	: Ptr;

PROCEDURE test(ch:CHAR);
BEGIN
{$R+ }
	ch := CHR(ORD(ch) MOD 128);	{--- this statement will fail with a CHECK ERROR ---}
	.
	.
END;

BEGIN
	.
	.
	p^ := $FF;
	.
	.
	test(CHAR(p^));
------------------------------------------------------------------------


MPW Pascal generates an EXT.W to widen the signedByte to a Word
(CHAR is word aligned),
thus $FF becomes $FFFF instead of $00FF and test falls over with a CHECK ERROR.

This may or may not be of interest to someone :-)

-- 
Michael Newbery

ACSnet:	newbery@vuwcomp.nz  UUCP: {ubc-vision,alberta}!calgary!vuwcomp!newbery
Une boule qui roule tue les poules.		(Landslides kill chickens)