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From: sandra@utah-cs.UUCP (Sandra J Loosemore)
Newsgroups: comp.sys.atari.st
Subject: Bug in Alcyon C v4.14
Message-ID: <4713@utah-cs.UUCP>
Date: Sat, 4-Jul-87 10:15:20 EDT
Article-I.D.: utah-cs.4713
Posted: Sat Jul  4 10:15:20 1987
Date-Received: Sat, 4-Jul-87 19:53:15 EDT
Organization: University of Utah CS Dept
Lines: 27
Keywords: bug pointer arithmetic

I've just run across a rather annoying bug in Alcyon C v4.14 (the developer's
kit C):  it has a hard time with adding a word-sized integer constant to
a pointer variable.  My code originally looked something like

    STRUCTURE *this, *next;
    next = this + sizeof(STRUCTURE);  /* sizeof(STRUCTURE) = 8192 */

and it was generating code like:

    add.l #$80000000,R0

No difference whether I used "sizeof" or hardwired in the constant directly,
same bad results.  I eventually got around the problem by doing

    next = this; next++;


In another place, I was doing something similar:

    STRUCTURE *this, *next;
    int n;
    next = this + n*sizeof(STRUCTURE);

and instead of generating a multiply it generated a CLR.L instruction!

-Sandra Loosemore
sandra@cs.utah.edu, sandra@utah-cs.uucpu