From 05da479f3f493525805e1e594c5f39735a473f65 Mon Sep 17 00:00:00 2001
From: "Guillermo J. Rozas" <edu/mit/csail/zurich/gjr>
Date: Mon, 24 Aug 1987 14:43:17 +0000
Subject: [PATCH] Displacements are simplified.  They no longer have to
 discriminate between @PCO and @PCR.

---
 v7/src/compiler/machines/vax/insmac.scm | 45 +++++--------------------
 v7/src/compiler/machines/vax/instr1.scm | 16 ++++-----
 2 files changed, 15 insertions(+), 46 deletions(-)

diff --git a/v7/src/compiler/machines/vax/insmac.scm b/v7/src/compiler/machines/vax/insmac.scm
index 1cc128bec..8f52a2dda 100644
--- a/v7/src/compiler/machines/vax/insmac.scm
+++ b/v7/src/compiler/machines/vax/insmac.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/machines/vax/insmac.scm,v 1.9 1987/08/23 07:56:16 jinx Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/machines/vax/insmac.scm,v 1.10 1987/08/24 14:39:29 jinx Exp $
 
 Copyright (c) 1987 Massachusetts Institute of Technology
 
@@ -126,15 +126,15 @@ MIT in each case. |#
 		    `(EA-VALUE ,(caddar fields)))
 	       ,tail)
 	     tail-size))
+	   ;; Displacements are like signed bytes.  They are a different
+	   ;; keyword to allow the disassembler to do its thing correctly.
 	   ((DISPLACEMENT)
-	    (let ((desc (cadar fields)))
-	      (let ((expression (cadr desc))
-		    (size (car desc)))
-		(receiver
-		 `(CONS-SYNTAX
-		   ,(displacement-syntaxer expression size)
-		   ,tail)
-		 (+ size tail-size)))))
+	    (let* ((desc (cadar fields))
+		   (size (car desc)))
+	      (receiver
+	       `(CONS-SYNTAX ,(integer-syntaxer (cadr desc) 'SIGNED size)
+			     ,tail)
+	       (+ size tail-size))))
 	   ((IMMEDIATE)
 	    (receiver
 	     `(CONS-SYNTAX
@@ -144,33 +144,6 @@ MIT in each case. |#
 	   (else
 	    (error "expand-fields: Unknown field kind" (caar fields))))))))
 
-(define (displacement-syntaxer expression size)
-  (cond ((not (pair? expression))
-	 `(SYNTAX-DISPLACEMENT ,expression
-			       ,(make-coercion-name 'SIGNED size)))
-	((eq? '@PCO (car expression))
-	 (integer-syntaxer (cadr expression) 'SIGNED size))
-	((eq? '@PCR (car expression))
-	 (nteger-syntaxer `(- ,(cadr expression)
-			      (+ *PC* ,(/ size 8))) 'SIGNED size))
-	(else
-	 `(SYNTAX-DISPLACEMENT ,expression
-			       ,(make-coercion-name 'SIGNED size)))))
-
-(define (syntax-displacement expression coercion)
-  (cond ((not (pair? expression))
-	 (error "syntax-displacement: bad displacement specifier"
-		expression))
-	((eq? (car expression) '@PCO)
-	 (syntax-evaluation (cadr expression) coercion))
-	((eq? (car expression) '@PCR)
-	 (syntax-evaluation `(- ,(cadr expression)
-				(+ *PC* ,(/ (coercion-size coercion) 8)))
-			    coercion))
-	(else
-	 (error "syntax-displacement: bad displacement specifier"
-		expression))))
-
 (define (collect-byte components tail receiver)
   (define (inner components receiver)
     (if (null? components)
diff --git a/v7/src/compiler/machines/vax/instr1.scm b/v7/src/compiler/machines/vax/instr1.scm
index bd30fdc1f..07f20d2b9 100644
--- a/v7/src/compiler/machines/vax/instr1.scm
+++ b/v7/src/compiler/machines/vax/instr1.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/machines/vax/instr1.scm,v 1.4 1987/08/19 04:40:53 jinx Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/machines/vax/instr1.scm,v 1.5 1987/08/24 14:43:17 jinx Exp $
 
 Copyright (c) 1987 Massachusetts Institute of Technology
 
@@ -42,7 +42,7 @@ MIT in each case. |#
 
 #|
 
-A) There are three types of operand specifiers:
+A) There are two types of operand specifiers:
 
     - General addressing mode operand specifier, with matching pattern syntax
 
@@ -52,14 +52,10 @@ A) There are three types of operand specifiers:
       Handbook", on Appendix E. 
       They are implemented in insutl.scm
 
-    - Displacement for branch instructions.  The matching pattern syntax is
-
-      (? value displacement)
-
-      This matches either (@PCO offset) or (@PCR label).
-
-    - Immediate operand.  Only the BUG instruction uses this.  The
-      matching syntax is (? value).      
+    - Immediate operands.  The matching syntax is (? value).  The operand
+      is processed appropriately by the body of the instruction definition.
+      It is used for instruction displacements (ie. the SOB instruction), or
+      immediate operands (ie. the BUG instruction).
 
 B) The instruction set is currently incomplete.  In particular, none
 of the instructions in chapters 14 or 16 are below.  The missing
-- 
2.25.1