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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
ZERO = "#0"
DEST_NONE = "_"
JUMP_NONE = ""
JUMPS_IF_NZERO = ["jgt", "jlt", "jne", "jmp"]
JUMPS_IF_ZERO = ["jge", "jle", "jeq", "jmp"]
ENDIANNESS = "little"
def decode_jump(ins: int) -> str:
if (ins & 0x7) == 0:
return JUMP_NONE
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 ZERO
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 DEST_NONE
def decode_instruction(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:
mnemonic, 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 [mnemonic, dest, op1, op2, jumpdest]
def fixup_ins(ins: int) -> list[str]:
(mnemonic, dest, op1, op2, jumpdest) = decode_instruction(ins)
# fixups
if op1 == ZERO:
# subtract something from #0 - subtraction
if mnemonic == "sub":
return ["neg", dest, op2, "", jumpdest]
# 0 AND something = 0
if mnemonic == "and":
# if no dest, only jump matters
if dest == DEST_NONE:
# jump always or jump-if-zero --> always jump
if jumpdest in JUMPS_IF_ZERO:
return ["jmp", "", "", "", ""]
# all other jumps? <, >, <>, nojmp
else:
return ["nop", "", "", "", ""]
else:
if jumpdest in JUMPS_IF_ZERO:
newjmp = "jmp"
else:
newjmp = ""
return ["mov", dest, ZERO, "", newjmp]
# 0 +/|/^ something = something
if mnemonic in ["add", "or", "xor"]:
if dest == DEST_NONE and jumpdest == JUMP_NONE:
return ["nop", "", "", "", ""]
else:
return ["mov", dest, op2, "", jumpdest]
# basically, not 0 == 0xFFFF....
# opposite of what AND is doing?
if mnemonic == "not":
# if no dest, only jump matters
if dest == DEST_NONE:
# 0xFFFF is not jgt, since highest bit is always signed.
if jumpdest in ["jeq", "jgt", "jge", JUMP_NONE]:
return ["nop", "", "", "", ""]
else:
return ["jmp", "", "", "", ""]
elif dest == DEST_NONE:
if mnemonic == "sub":
return ["cmp", "", op1, op2, jumpdest]
return [mnemonic, dest, op1, op2, jumpdest]
def print_decoded(ins: int, simplify: bool) -> str:
if simplify:
(mnemonic, dest, op1, op2, jumpdest) = fixup_ins(ins)
else:
(mnemonic, dest, op1, op2, jumpdest) = decode_instruction(ins)
jumpdest_str = f".{jumpdest}" if jumpdest else ""
opcode_str = f"{mnemonic}{jumpdest_str}"
dest_str = f"{dest}, " if dest else 7 * " "
op2_str = ", " if op2 else ""
op1_str = f"{op1}{op2_str}"
return f"{opcode_str:<9}{dest_str:<6}{op1_str:<4}{op2}"
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, byteorder=ENDIANNESS)
if ENDIANNESS in ["big", "be"]:
raw_ins = f"{insb[0]:02x} {insb[1]:02x}"
elif ENDIANNESS in ["little", "le"]:
raw_ins = f"{insb[1]:02x} {insb[0]:02x}"
else:
raw_ins = f"?? ??"
decoded_ins = print_decoded(ins, False)
decoded_ins2 = print_decoded(ins, True)
if decoded_ins == decoded_ins2:
line = f"\t{raw_ins}\t{decoded_ins}"
else:
line = f"\t{raw_ins}\t{decoded_ins2:<25}; {decoded_ins}"
print(line)
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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