Added some comment

lang/m2/libm2/ChkCards.e

@@ -103,7 +103,7 @@
  lol 0
  cmu EM_WSIZE
  zge *1
- loc M2_UOVFL
+ loc M2_UUVFL
  trp
 1
  lol EM_WSIZE
@@ -119,7 +119,7 @@
  ldl 0
  cmu EM_LSIZE
  zge *1
- loc M2_UOVFL
+ loc M2_UUVFL
  trp
 1
  ldl EM_LSIZE

lang/m2/libm2/EM.e

@@ -73,13 +73,16 @@
 ; SIG is called with one parameter:
 ;       - procedure instance identifier (PROC)
 ; and returns the old traphandler.
-; only the procedure identifier inside the PROC is used.
 
+ exa _handler
  exp $SIG
  pro $SIG, 0
+ lae _handler
+ loi EM_PSIZE
  lal PROC
  loi EM_PSIZE
- sig
+ lae _handler
+ sti EM_PSIZE
  ret EM_PSIZE
  end ?
 

lang/m2/libm2/Storage.def

@@ -5,6 +5,12 @@ DEFINITION MODULE Storage;
   Version:	$Header$
 *)
 
+(*
+  Wirth's 3rd edition certainly is confusing: mostly it uses Allocate, but
+  the module at the end of the book defines ALLOCATE. To avoid problems,
+  I included them both.
+*)
+
 	FROM SYSTEM IMPORT ADDRESS;
 
 	PROCEDURE ALLOCATE(VAR a : ADDRESS; size : CARDINAL);
@@ -13,11 +19,17 @@ DEFINITION MODULE Storage;
 	   killed.
 	*)
 
+	PROCEDURE Allocate(VAR a : ADDRESS; size : CARDINAL);
+	(* Identical to ALLOCATE *)
+
 	PROCEDURE DEALLOCATE(VAR a : ADDRESS; size : CARDINAL);
 	(* Free the area at address "a" with the given size. The area
 	   must have been allocated by "ALLOCATE", with the same size.
 	*)
 
+	PROCEDURE Deallocate(VAR a : ADDRESS; size : CARDINAL);
+	(* Identical to DEALLOCATE *)
+
 	PROCEDURE Available(size : CARDINAL) : BOOLEAN;
 	(* Return TRUE if an area with the given size could be allocated.
 	*)

lang/m2/libm2/Storage.mod

@@ -52,7 +52,7 @@ IMPLEMENTATION MODULE Storage;
 	Compacted: BOOLEAN;		(* avoid recursive reorganization *)
 	FirstBlock: BucketPtr;
 
-  PROCEDURE Allocate(size: CARDINAL) : ADDRESS;
+  PROCEDURE MyAllocate(size: CARDINAL) : ADDRESS;
     VAR	nu : INTEGER;
 	b : INTEGER;
 	p, q: BucketPtr;
@@ -141,7 +141,7 @@ IMPLEMENTATION MODULE Storage;
 	IF brk = ILLBREAK THEN
 		ReOrganize();
 		Compacted := TRUE;
-		brk := Allocate(size);
+		brk := MyAllocate(size);
 		Compacted := FALSE;
 		RETURN brk;
 	END;
@@ -150,11 +150,16 @@ IMPLEMENTATION MODULE Storage;
 	p^.BSIZE := nu;
 	p^.BNEXT := USED;
 	RETURN ADR(p^.BSTORE);
+  END MyAllocate;
+
+  PROCEDURE Allocate(VAR a: ADDRESS; size: CARDINAL);
+  BEGIN
+	ALLOCATE(a, size);
   END Allocate;
 
   PROCEDURE ALLOCATE(VAR a: ADDRESS; size: CARDINAL);
   BEGIN
-	a := Allocate(size);
+	a := MyAllocate(size);
 	IF a = NIL THEN
 		Message("out of core");
 		HALT;
@@ -164,7 +169,7 @@ IMPLEMENTATION MODULE Storage;
   PROCEDURE Available(size: CARDINAL): BOOLEAN;
     VAR	a: ADDRESS;
   BEGIN
-	a:= Allocate(size);
+	a:= MyAllocate(size);
 	IF a # NIL THEN
 		DEALLOCATE(a, size);
 		RETURN TRUE;
@@ -172,6 +177,11 @@ IMPLEMENTATION MODULE Storage;
 	RETURN FALSE;
   END Available;
 
+  PROCEDURE Deallocate(VAR a: ADDRESS; size: CARDINAL);
+  BEGIN
+	DEALLOCATE(a, size);
+  END Deallocate;
+
   PROCEDURE DEALLOCATE(VAR a: ADDRESS; size: CARDINAL);
     VAR	p: BucketPtr;
   BEGIN

lang/m2/libm2/Traps.def

@@ -15,6 +15,7 @@ DEFINITION MODULE Traps;
 	ERRFORLOOP =	68;	(* value of FOR-loop control variable changed
 				   in loop
 				*)
+	ERRCARDUVFL =	69;	(* CARDINAL underflow *)
 
   TYPE	TrapHandler = EM.TrapHandler;
 

lang/m2/libm2/catch.c

@@ -45,6 +45,7 @@ static struct errm {
 	{ M2_NORESULT,	"no RETURN from procedure function"},
 	{ M2_UOVFL,	"cardinal overflow"},
 	{ M2_FORCH,	"Warning: FOR-loop control variable was changed in the body"},
+	{ M2_UUVFL,	"cardinal underflow"},
 	{ -1,		0}
 };
 

lang/m2/libm2/head_m2.e

@@ -13,6 +13,7 @@
 
 #define STACKSIZE	2048	/* maximum stack size for a coroutine */
 
+ exa _handler
  exa _environ
  exa _argv
  exa _argc
@@ -23,6 +24,8 @@
  exa _StackSize
  exp $_catch
 
+_handler
+ bss EM_PSIZE,0,0
 _environ
  bss EM_PSIZE,0,0
 _argv
@@ -42,6 +45,16 @@ _StackSize
 mainroutine
  bss 2*EM_PSIZE,0,0
 
+ inp $trap_handler
+ pro $trap_handler,0
+ lol 0	; trap number
+ lae _handler
+ loi EM_PSIZE
+ cai
+ asp EM_WSIZE
+ rtt
+ end 0
+
  exp $m_a_i_n
  pro $m_a_i_n, STACKSIZE
 
@@ -78,7 +91,7 @@ mainroutine
  lol 0
  ste _argc		; save argument count
 
- lpi $_catch
+ lpi $trap_handler
  sig
  asp EM_PSIZE
  cal $_M2M