Patching a packed config word

Packed configuration words are a common place where immutable and mutable bit strings are useful together. Build or receive the word as a Tibs, promote it to Mutibs while editing individual fields, then keep the patched value as ordinary binary data.

from tibs import Tibs


ENABLED_BIT = 0
DEBUG_BIT = 1
MODE = slice(2, 5)
RETRY_LIMIT = slice(5, 9)
TIMEOUT_SECONDS = slice(9, 16)


def build_config(enabled, debug, mode, retry_limit, timeout_seconds):
    return Tibs.from_joined([
        [enabled, debug],
        Tibs.from_u(mode, 3),
        Tibs.from_u(retry_limit, 4),
        Tibs.from_u(timeout_seconds, 7),
    ])


def parse_config(config):
    return {
        "enabled": config[ENABLED_BIT],
        "debug": config[DEBUG_BIT],
        "mode": config[MODE].u,
        "retry_limit": config[RETRY_LIMIT].u,
        "timeout_seconds": config[TIMEOUT_SECONDS].u,
    }


config = build_config(
    enabled=True,
    debug=False,
    mode=1,
    retry_limit=3,
    timeout_seconds=65,
)

assert config.hex == "89c1"
assert parse_config(config) == {
    "enabled": True,
    "debug": False,
    "mode": 1,
    "retry_limit": 3,
    "timeout_seconds": 65,
}

patched = config.to_mutibs()
patched.unset(ENABLED_BIT)
patched.set(DEBUG_BIT)
patched[MODE] = Tibs.from_u(4, 3)
patched[RETRY_LIMIT] = Tibs.from_u(10, 4)

assert patched.hex == "6541"
assert parse_config(patched) == {
    "enabled": False,
    "debug": True,
    "mode": 4,
    "retry_limit": 10,
    "timeout_seconds": 65,
}

This example uses normal Python slices for fields whose positions are counted from the left. For specifications that label fields from the least significant bit, use the view helpers described in Views.