1984-07-20 10:44:57 +00:00
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1984-07-20 11:03:31 +00:00
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; $Header$
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1984-07-20 10:44:57 +00:00
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; (c) copyright 1983 by the Vrije Universiteit, Amsterdam, The Netherlands.
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;
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; This product is part of the Amsterdam Compiler Kit.
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;
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; Permission to use, sell, duplicate or disclose this software must be
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; obtained in writing. Requests for such permissions may be sent to
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;
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; Dr. Andrew S. Tanenbaum
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; Wiskundig Seminarium
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; Vrije Universiteit
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; Postbox 7161
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; 1007 MC Amsterdam
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; The Netherlands
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;
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mes 2,EM_WSIZE,EM_PSIZE
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; procedure encaps(procedure p; procedure(q(n:integer));
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; {call q if a trap occurs during the execution of p}
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; {if q returns, continue execution of p}
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inp $handler
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#define PIISZ 2*EM_PSIZE
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#define PARG 0
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#define QARG PIISZ
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#define E_ELB -EM_PSIZE
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#define E_EHA -2*EM_PSIZE
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; encaps is called with two parameters:
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; - procedure instance identifier of q (QARG)
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; - procedure instance identifier of p (PARG)
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; and two local variables:
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; - the lb of the previous encaps (E_ELB)
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; - the procedure identifier of the previous handler (E_EHA)
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;
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; One static variable:
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; - the lb of the currently active encaps (enc_lb)
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enc_lb
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bss EM_PSIZE,0,0
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exp $encaps
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pro $encaps,PIISZ
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; save lb of previous encaps
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lae enc_lb
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loi EM_PSIZE
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lal E_ELB
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sti EM_PSIZE
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; set new lb
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lxl 0
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lae enc_lb
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sti EM_PSIZE
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; save old handler id while setting up the new handler
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lpi $handler
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sig
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lal E_EHA
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sti EM_PSIZE
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; handler is ready, p can be called
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; p doesn't expect parameters except possibly the static link
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; always passing the link won't hurt
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lal PARG
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loi PIISZ
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cai
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asp EM_PSIZE
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; reinstate old handler
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lal E_ELB
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loi EM_PSIZE
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lae enc_lb
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sti EM_PSIZE
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lal E_EHA
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loi EM_PSIZE
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sig
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asp EM_PSIZE
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ret 0
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end ?
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#define TRAP 0
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#define H_ELB -EM_PSIZE
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; handler is called with one parameter:
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; - trap number (TRAP)
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; one local variable
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; - the current LB of the enclosing encaps (H_ELB)
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pro $handler,EM_PSIZE
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; save LB of nearest encaps
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lae enc_lb
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loi EM_PSIZE
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lal H_ELB
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sti EM_PSIZE
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; fetch setting for previous encaps via LB of nearest
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lal H_ELB
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loi EM_PSIZE
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adp E_ELB
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loi EM_PSIZE ; LB of previous encaps
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lae enc_lb
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sti EM_PSIZE
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lal H_ELB
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loi EM_PSIZE
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adp E_EHA
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loi EM_PSIZE ; previous handler
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sig
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asp EM_PSIZE
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; previous handler is re-instated, time to call Q
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lol TRAP ; the one and only real parameter
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lal H_ELB
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loi EM_PSIZE
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lpb ; argument base of enclosing encaps
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adp QARG
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loi PIISZ
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exg EM_PSIZE
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dup EM_PSIZE ; The static link is now on top
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zer EM_PSIZE
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cmp
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zeq *1
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; non-zero LB
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exg EM_PSIZE
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cai
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asp EM_WSIZE+EM_PSIZE
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bra *2
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1
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; zero LB
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asp EM_PSIZE
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cai
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asp EM_WSIZE
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2
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; now reinstate handler for continued execution of p
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lal H_ELB
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loi EM_PSIZE
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lae enc_lb
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sti EM_PSIZE
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lpi $handler
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sig
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asp EM_PSIZE
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rtt
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end ?
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