Convert Brainfuck code (bigints, unsigned, saturating when going below 0) to Rui code that runs in drui.c.

bf2rui.py

# Convert Brainfuck code written for saturating unsigned bigint cells into Rui code.
# Targets the Rui variant implemented by drui.c, using R and W for ASCII I/O.

import sys
import re
from textwrap import dedent as _


SIZE = 9999

program = [f""":7
={SIZE}
:3
=1
:5
=1~.$!
"""]
line = 7

with open(sys.argv[1]) as f:
    code = f.read()

stack = []
i = 0
while i < len(code):
    c = code[i]
    i += 1

    if c == "+":
        # this is the only one of the repeated-instruction optimizations that is trivial; the commands - > < are more complex and much harder to optimize
        e = 1
        while code[i] == "+":
            i += 1
            e += 1
        if e == 1:
            program.append("+4.")
        else:
            program.append(f"={e}*4=0")
    elif c == "-":
        program.append("-1+6..*5=0")
    elif c == ">":
        program.append("-1*2=1~=0")
    elif c == "<":
        program.append(f"=1$-{SIZE}*4.")
    elif c == ",":
        program.append("-1R*4.")
    elif c == ".":
        program.append("-1W*4.")
    elif c == "[":
        if code[i:i+2] == "-]":
            # clear loop
            program.append("-1")
            i += 2
        else:
            line += 1
            program.append(_(f"""
            -1*{line+1}*4=0:"""))
            stack.append((line, len(program)))
            program.append(None)
            program.append(_("""
            ..-0"""))
            line += 1
    elif c == "]":
        start, idx = stack.pop()
        program.append(_(f""":{start}
        """))
        line += 1
        program[idx] = str(line)
program.append(f"={SIZE}~-0!")

with open(sys.argv[2], "w") as f:
    f.write("".join(program))