# HG changeset patch
# User Simon Heath <icefox@dreamquest.io>
# Date 1664859776 14400
#      Tue Oct 04 01:02:56 2022 -0400
# Node ID 3e06b7fe0e3ae228494f478b1c9fe486284cb953
# Parent  1ad37d61b1c070ea60c87c695d11e69156fcd5a0
Ok I'm not insane just foolish

diff --git a/src/main.fnl b/src/main.fnl
--- a/src/main.fnl
+++ b/src/main.fnl
@@ -49,6 +49,8 @@
 ;
 ; enum OpMode {iABC, iABx, iAsBx, iAx, isJ};  /* basic instruction formats */
 
+(local fennel (require :fennel))
+
 ;; Opcodes with metadata, as listed in lopcodes.h
 ;;
 ;; `code` is the integer ID of the opcode from the Lua OpCode struct
@@ -174,11 +176,17 @@
 
 (fn opcode-idx [op]
   "Returns the opcode number of the given opcode name"
-  (- (. OpcodeNames op) 1))
+   (let [v (- (. OpcodeNames op) 1)]
+     (if v
+       v
+       (error (string.format "Invalid opcode name %s" op)))))
 
 (fn idx-opcode [i]
   "Returns the opcode struct for the opcode with the given number"
-  (. Opcodes (+ i 1)))
+  (let [v (. Opcodes (+ i 1))]
+     (if v
+       v
+       (error (string.format "Invalid opcode index %s" i)))))
 
 (fn extract [i offset len]
   "Extract `len` bits of integer `i`, starting from bit `offset`
@@ -191,7 +199,11 @@
 
 (fn decode-abc [i]
   "Decode an instruction in the :iABC format"
-  0)
+  (let [a (extract i 7 8)
+        k (extract i 15 1)
+        b (extract i 16 8)
+        c (extract i 24 8)]
+    {: a : b : c : k}))
 
 (fn decode-abx [i]
   "Decode an instruction in the :iABx format"
@@ -215,12 +227,12 @@
         OpPos  0   ; Starting bit number of the opcode field
         opcode (extract i OpPos OpSize)
         opcode-format (. (idx-opcode opcode) :format)]
-    (print (string.format "Instruction %d is opcode %i named %s with format %s"
+    (print (string.format "Instruction 0x%X is opcode %i named %s with format %s %s"
                           i
                           opcode
                           (. (idx-opcode opcode) :name)
-                          opcode-format))))
+                          opcode-format
+                          (fennel.view (decode-abc i))))))
 
-(print "Opcode" 3 "is" (. (idx-opcode 3) :name))
-(print "Opcode :OpGetI is" (opcode-idx :OpGetI))
-(decode 0x03)
+(decode 0x11223303)
+