gistfile1.py

import sys

if len(sys.argv) < 3:
    print("Usage: {} [-d] <file> <n>".format(sys.argv[0]))
    sys.exit()

debug = False
if sys.argv[1] == "-d":
    sys.argv.pop(1)
    debug = True


source_lines = []
tags = {}



# Preprocessing.
orig_lines = [line.strip() for line in open(sys.argv[1])]
for linenr, line in enumerate(orig_lines):
    if "#" in line:
        line = line[:line.index("#")]

    if ":" in line:
        tag, line = line.split(":")
        tags[tag.strip()] = len(source_lines)

    line = line.strip()
    if line: source_lines.append((linenr + 1, line))


# Compile to VM bytecode
INCX = 0
INCY = 1
HALT = 2
PRINTX = 3
JMP = 4
DJZX = 5
DJZY = 6

bytecode = []
debug_lines = {}
for linenr, line in source_lines:
    debug_lines[len(bytecode)] = orig_lines[linenr - 1]

    args = line.split()
    if line == "INCX": bytecode.append(INCX)
    elif line == "INCY": bytecode.append(INCY)
    elif line == "HALT": bytecode.append(HALT)
    elif line == "PRINTX": bytecode.append(PRINTX)
    elif len(args) == 2 and args[0] in {"JMP", "DJZX", "DJZY"}:
        if args[1] not in tags:
            print("Unknown jump location {} on line {}:\n{}".format(args[1], linenr, line))
            sys.exit(1)

        bytecode.append((4 + ["JMP", "DJZX", "DJZY"].index(args[0])) | tags[args[1]] << 4)
    else:
        print("Unknown instruction on line {}:\n{}".format(linenr, line))
        sys.exit(1)


# Execute
X = int(sys.argv[2])
Y = 0
isp = 0

while True:
    if isp > len(bytecode):
        print("Execution fell off end of program.")
        sys.exit(1)

    if debug:
        print(X, Y, debug_lines[isp])

    arg0 = bytecode[isp] & 0xf
    arg1 = bytecode[isp] >> 4
    isp += 1

    if   arg0 == 0: X += 1
    elif arg0 == 1: Y += 1
    elif arg0 == 2: break
    elif arg0 == 3: print(X)
    elif arg0 == 4: isp = arg1
    elif arg0 == 5:
        if X == 0: isp = arg1
        else: X -= 1
    elif arg0 == 6:
        if Y == 0: isp = arg1
        else: Y -= 1