Initial revision

2005-04-21 14:53:53 +00:00
commit 9865aeaa79
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+#
+
+
+; $Header$
+;  (c) copyright 1983 by the Vrije Universiteit, Amsterdam, The Netherlands.
+; 
+;           This product is part of the Amsterdam Compiler Kit.
+; 
+;  Permission to use, sell, duplicate or disclose this software must be
+;  obtained in writing. Requests for such permissions may be sent to
+; 
+;       Dr. Andrew S. Tanenbaum
+;       Wiskundig Seminarium
+;       Vrije Universiteit
+;       Postbox 7161
+;       1007 MC Amsterdam
+;       The Netherlands
+; 
+
+ mes 2,_EM_WSIZE,_EM_PSIZE
+
+; procedure encaps(procedure p; procedure(q(n:integer));
+; {call q if a trap occurs during the execution of p}
+; {if q returns, continue execution of p}
+
+
+ inp $handler
+
+#define PIISZ   2*_EM_PSIZE
+
+#define PARG    0
+#define QARG    PIISZ
+#define E_ELB   0-_EM_PSIZE
+#define E_EHA   -2*_EM_PSIZE
+
+; encaps is called with two parameters:
+;       - procedure instance identifier of q (QARG)
+;       - procedure instance identifier of p (PARG)
+; and two local variables:
+;       - the lb of the previous encaps      (E_ELB)
+;       - the procedure identifier of the previous handler (E_EHA)
+;
+; One static variable:
+;       - the lb of the currently active encaps (enc_lb)
+
+enc_lb
+        bss _EM_PSIZE,0,0
+
+ exp $encaps
+ pro $encaps,PIISZ
+ ; save lb of previous encaps
+ lae enc_lb
+ loi _EM_PSIZE
+ lal E_ELB
+ sti _EM_PSIZE
+ ; set new lb
+ lxl 0
+ lae enc_lb
+ sti _EM_PSIZE
+ ; save old handler id while setting up the new handler
+ lpi $handler
+ sig
+ lal E_EHA
+ sti _EM_PSIZE
+ ; handler is ready, p can be called
+ ; p doesn't expect parameters except possibly the static link
+ ; always passing the link won't hurt
+ lal PARG
+ loi PIISZ
+ cai
+ asp _EM_PSIZE
+ ; reinstate old handler
+ lal E_ELB
+ loi _EM_PSIZE
+ lae enc_lb
+ sti _EM_PSIZE
+ lal E_EHA
+ loi _EM_PSIZE
+ sig
+ asp _EM_PSIZE
+ ret 0
+ end ?
+
+#define TRAP    0
+#define H_ELB   0-_EM_PSIZE
+
+; handler is called with one parameter:
+;       - trap number (TRAP)
+; one local variable
+;       - the current LB of the enclosing encaps (H_ELB)
+
+
+ pro $handler,_EM_PSIZE
+ ; save LB of nearest encaps
+ lae enc_lb
+ loi _EM_PSIZE
+ lal H_ELB
+ sti _EM_PSIZE
+ ; fetch setting for previous encaps via LB of nearest
+ lal H_ELB
+ loi _EM_PSIZE
+ adp E_ELB
+ loi _EM_PSIZE   ; LB of previous encaps
+ lae enc_lb
+ sti _EM_PSIZE
+ lal H_ELB
+ loi _EM_PSIZE
+ adp E_EHA
+ loi _EM_PSIZE   ; previous handler
+ sig
+ asp _EM_PSIZE
+ ; previous handler is re-instated, time to call Q
+ lol TRAP       ; the one and only real parameter
+ lal H_ELB
+ loi _EM_PSIZE
+ lpb            ; argument base of enclosing encaps
+ adp QARG
+ loi PIISZ
+ exg _EM_PSIZE
+ dup _EM_PSIZE   ; The static link is now on top
+ zer _EM_PSIZE
+ cmp
+ zeq *1
+ ; non-zero LB
+ exg _EM_PSIZE
+ cai
+ asp _EM_WSIZE+_EM_PSIZE
+ bra *2
+1
+ ; zero LB
+ asp _EM_PSIZE
+ cai
+ asp _EM_WSIZE
+2
+ ; now reinstate handler for continued execution of p
+ lal H_ELB
+ loi _EM_PSIZE
+ lae enc_lb
+ sti _EM_PSIZE
+ lpi $handler
+ sig
+ asp _EM_PSIZE
+ rtt
+ end ?