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#!/usr/bin/env python3
"""
Disassembler for nandgame.
Using my own flavor of assembly language.
I don't like the "C-style" one nandgame introduces.
"""
import sys
def decode_jump(ins: int) -> str:
if (ins & 0x7) == 0:
return ""
if (ins & 0x7) == 0x7:
return "jmp"
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 "jlt"
if je:
return "jeq"
if jg:
return "jgt"
return "<unknown>"
# return op, and whether it's a one-op or two-op
def decode_ins(ins: int) -> (str, bool):
opcode = (ins >> 8) & 0x03
ar_n_log = (ins & (1 << 10)) != 0
opcode |= ar_n_log << 2
if opcode == 0b000:
return "and", True
if opcode == 0b001:
return "or", True
if opcode == 0b010:
return "xor", True
if opcode == 0b011:
return "not", False
if opcode == 0b100:
return "add", True
if opcode == 0b101:
return "inc", False
if opcode == 0b110:
return "sub", True
if opcode == 0b111:
return "dec", False
return "<?>"
# normally, X = arg1 = D
def decode_arg1(ins: int) -> str:
use_mem = (ins & (1 << 12)) != 0
zx = (ins & (1 << 7)) != 0
sw = (ins & (1 << 6)) != 0
if zx:
return "#0"
if not sw:
return "D"
return "M" if use_mem else "A"
# normally, Y = arg2 = A
def decode_arg2(ins: int) -> str:
use_mem = (ins & (1 << 12)) != 0
# don't care, only X is zeroed
# zx = (ins & (1 << 7)) != 0
sw = (ins & (1 << 6)) != 0
if sw:
return "D"
return "M" if use_mem else "A"
def decode_dest(ins: int) -> str:
dA = (ins & (1 << 5)) != 0
dD = (ins & (1 << 4)) != 0
dM = (ins & (1 << 3)) != 0
dest = ""
if dA:
dest += "A"
if dD:
dest += "D"
if dM:
dest += "M"
return dest if dest else "_"
def decode_instruction_complete(ins: int) -> list[str]:
"""
Will return a 5 element list/tuple/whatever
mnemonic, destination, X, Y, jumpdest
"""
if ins & 0x8000 == 0:
# mov? ldr? ldi? aaaaaaaaaaa....
return ["mov", "A", f"#{ins}", "", ""]
else:
codename, two_op = decode_ins(ins)
dest = decode_dest(ins)
op1 = decode_arg1(ins)
op2 = decode_arg2(ins) if two_op else ""
jumpdest = decode_jump(ins)
return [codename, dest, op1, op2, jumpdest]
def print_decoded(ins: int) -> str:
(codename, dest, op1, op2, jumpdest) = decode_instruction_complete(ins)
dest_str = f"{dest}, " if dest else 7 * " "
op1_str = f"{op1}{", " if op2 else ""}"
jumpdest_str = f"; {jumpdest}" if jumpdest else ""
return f"{codename:<5}{dest_str:<6}{op1_str:<4}{op2:<5}{jumpdest_str}"
def main():
if len(sys.argv) != 2:
print(f"Usage: {sys.argv[0]} [filename]")
sys.exit(1)
try:
filename = sys.argv[1]
with open(filename, "rb") as f:
while True:
insb = f.read(2)
if not insb:
break
ins = int.from_bytes(insb)
print(f"\t{insb[0]:02x} {insb[1]:02x}\t{print_decoded(ins)}")
except FileNotFoundError:
print(f"File {filename} not found.")
sys.exit(1)
# head, tail...
except BrokenPipeError:
sys.exit(0)
if __name__ == "__main__":
main()
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