island-story/scripts/convert_fixed_point.py

import argparse


def convert_to(dec_str: str) -> None:
    str_parts = dec_str.split(".")
    assert len(str_parts) == 2

    whole_str, part_str = str_parts
    whole_dec = int(whole_str)
    part_dec = float(f"0.{part_str}")
    part_bits = []
    for i in range(1, 9, 1):
        bit = "0"
        sub = 1 / (1 << i)
        if part_dec > sub:
            bit = "1"
            part_dec = part_dec - sub
        part_bits.append(bit)
    part_dec = int("".join(part_bits), 2)

    assert whole_dec <= 0xFF
    assert part_dec <= 0xFF

    print(f"0x{bytes([whole_dec, part_dec]).hex()}")


def convert_from(hex_str: str) -> None:
    assert hex_str.startswith("0x")
    assert len(hex_str) == 6

    whole_bin = int(hex_str[2:4], 16)
    # TODO: support negatives
    # if whole_bin & (1 << 7):
    # whole_bin = -
    part_bin = int(hex_str[4:6], 16)

    part_dec = 0
    for i in range(1, 9, 1):
        mask = 1 << (8 - i)
        if part_bin & mask:
            part_dec += 1 / (1 << i)

    print(f"{whole_bin + part_dec}")


def main() -> None:
    parser = argparse.ArgumentParser("convert_fixed_point")
    parser.add_argument("-d", "--decode", action="store_true")
    parser.add_argument("decimal")

    args = parser.parse_args()
    if args.decode:
        convert_from(args.decimal)
    else:
        convert_to(args.decimal)


if __name__ == "__main__":
    main()