From d0d0ca23ec689032df1be1ad285f8cbe03c66e19 Mon Sep 17 00:00:00 2001
From: Dane Johnson <daneallenjohnson@protonmail.com>
Date: Mon, 25 Aug 2025 12:34:08 -0500
Subject: [PATCH] More useful error messages, assume unsigned ints

---
 scmvm/assembler.scm |  2 +-
 scmvm/vm.scm        | 22 ++++++++++++++--------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/scmvm/assembler.scm b/scmvm/assembler.scm
index ad527a1..501f6f7 100644
--- a/scmvm/assembler.scm
+++ b/scmvm/assembler.scm
@@ -49,7 +49,7 @@
 
 (define (write-word word)
   (define bv (make-bytevector 4))
-  (bytevector-s32-native-set! bv 0 word)
+  (bytevector-u32-native-set! bv 0 word)
   (write-bytevector bv))
 
 (define (assembly-pass seq labels)
diff --git a/scmvm/vm.scm b/scmvm/vm.scm
index 7d7fa41..f2f921d 100644
--- a/scmvm/vm.scm
+++ b/scmvm/vm.scm
@@ -6,13 +6,14 @@
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-43)
+  #:use-module (ice-9 format)
   #:export (make-stack (push . stack-push) (pop . stack-pop) (peek . stack-peek) stack-ref stack->list
-	    (make-vm* . make-vm) run-vm
-    	    vm-memory-ref vm-memory-byte-ref vm-memory-set! vm-memory vm-load-program!
-	    vm-data-stack vm-ret-stack
-	    vm-debugger vm-debugger-set!
-            vm-pc vm-pc-set!
-            *instruction-set* instruction-type instruction-code))
+		       (make-vm* . make-vm) run-vm
+    		       vm-memory-ref vm-memory-byte-ref vm-memory-set! vm-memory vm-load-program!
+		       vm-data-stack vm-ret-stack
+		       vm-debugger vm-debugger-set!
+		       vm-pc vm-pc-set!
+		       *instruction-set* instruction-type instruction-code))
 
 ;;; Data Structures
 (define *stack-size* 512)
@@ -114,12 +115,16 @@
     (swap   #x17)
     (rot    #x18)
     (over   #x19)
+    (not    #x1a)
     (bye    #xff)))
 
 (define instruction-code cadr)
 
 (define (op-lookup code)
-  (car (find (lambda (x) (= (instruction-code x) code)) *instruction-set*)))
+  (let ([op (find (lambda (x) (= (instruction-code x) code)) *instruction-set*)])
+    (if op
+	(car op)
+	(error (format #f "tried to execute non-existant instruction ~x" code)))))
 
 (define (binop-lookup op)
   (case (op-lookup op)
@@ -129,7 +134,8 @@
     [(or) logior]
     [(nand) (compose lognot logand)]
     [(nor) (compose lognot logior)]
-    [(xor) logxor]))
+    [(xor) logxor]
+    [(not) lognot]))
 
 (define (relop-lookup op)
   (case (op-lookup op)