From e0971f599e8034f58b80743eacb7ce7f68d293ef Mon Sep 17 00:00:00 2001
From: uvok
Date: Sun, 4 Jan 2026 14:26:37 +0100
Subject: decode op and jumps

---
 nandgame/assembler/disas.py | 51 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/nandgame/assembler/disas.py b/nandgame/assembler/disas.py
index a68acf4..402df5c 100755
--- a/nandgame/assembler/disas.py
+++ b/nandgame/assembler/disas.py
@@ -6,12 +6,61 @@ if len(sys.argv) != 2:
     print(f"Usage: {sys.argv[0]} [filename]")
     sys.exit(1)
 
+def decode_jump(ins: int) -> str:
+    if (ins & 0x7) == 0:
+        return ""
+    if (ins & 0x7) == 0x7:
+        return "; j"
+
+    jl = (ins & (1<<2)) != 0
+    je = (ins & (1<<1)) != 0
+    jg = (ins & (1<<0)) != 0
+
+    # implied: and not jg
+    if (jl and je): return "; jle"
+    # implied: and not je
+    if (jl and jg): return "; jne"
+    # implied: and not je
+    if (je and jg): return "; jge"
+
+    # implied: only one flag is 1
+    if (jl): return "; jl"
+    if (je): return "; je"
+    if (jg): return "; jg"
+
+    return "; <unknown>"
+
+
+def decode_ins(ins: int) -> str:
+    opcode = (ins >> 8) & 0x03
+    ar_n_log = (ins & (1<<10)) != 0
+    opcode |= (ar_n_log << 2)
+
+    if opcode == 0b000: return "AND"
+    if opcode == 0b001: return "OR"
+    if opcode == 0b010: return "XOR"
+    if opcode == 0b011: return "NEG"
+    if opcode == 0b100: return "ADD"
+    if opcode == 0b101: return "INC"
+    if opcode == 0b110: return "SUB"
+    if opcode == 0b111: return "DEC"
+
+    return "<?>"
+
 def decode(ins: int) -> str:
     if (ins & 0x8000 == 0):
         # mov? ldr? ldi? aaaaaaaaaaa....
         return f"mov A, #{ins}"
     else:
-        return "<unknown>"
+        use_mem = (ins & (1<<12)) != 0
+        zx = (ins & (1<<7)) != 0
+        sw = (ins & (1<<6)) != 0
+        dA = (ins & (1<<5)) != 0
+        dD = (ins & (1<<4)) != 0
+        dM = (ins & (1<<3)) != 0
+
+        codename = decode_ins(ins)
+        return f"{codename:<5}<unknown>{decode_jump(ins)}"
 
 try:
     with open(sys.argv[1], "rb") as f:
-- 
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