Fix u64 support

[LelsersLasers]

If you use i64, you run into issues with u64 -> i64. Now uses i128. Looks like can_dbc has not considered this as well?

[Copilot]

Pull request overview

This PR updates the decoding/encoding pipeline to correctly handle 64-bit unsigned raw signal values by widening internal/public “raw value” representations and adjusting signed conversion logic.

Changes:

• Widened decoded raw signal storage from i64 to i128 to represent full u64 ranges without wraparound.
• Updated enum value-description mapping to use i128 keys and aligned decoding lookups accordingly.
• Simplified signed sign-extension during decoding and fixed signed-range computation during encoding to avoid overflow at 64-bit widths.

Comments suppressed due to low confidence (2)

src/lib.rs:144

• This changes a public API type (DecodedSignalValue::raw and related constructors) from i64 to i128, which is a breaking change for downstream crates. Consider introducing a public type alias (e.g., pub type RawSignalValue = i128) and using that in the struct/constructors to make the API change explicit and reduce future churn (and to help callers migrate by updating a single import/type).

/// Represents the decoded value of a CAN signal.
#[derive(Debug, Clone)]
pub struct DecodedSignalValue {
    /// The physical value of the signal after applying scaling and offset.
    pub physical: f64,
    /// Contains the raw integer value (with sign accounting).
    /// Present unless the signal is an IEEE float/double.
    pub raw: Option<i128>,
    /// If the signal/value has an enum mapping, this contains the corresponding enum label.
    pub enum_label: Option<String>,
}

impl DecodedSignalValue {
    /// Creates a new `DecodedSignalValue` for a numeric signal that is backed by
    /// an integer (signed or unsigned).
    pub fn new_integer_backed_numeric(physical: f64, raw_value: i128) -> Self {
        Self {
            physical,
            raw: Some(raw_value),
            enum_label: None,

src/lib.rs:241

• SignalMeta is a public struct, and changing enum_map keys from i64 to i128 is another breaking API change. If the wider goal is to support u64-sized raw values, consider also using the same exported raw-value type alias for this map key so the public surface stays consistent and easier to migrate.

/// Also includes the signal-level description/comment from the DBC, if available.
#[derive(Debug, Clone, Default)]
pub struct SignalMeta {
    /// Maps raw signal values to string enum labels from DBC value descriptions.
    pub enum_map: std::collections::HashMap<i128, String>,

    /// The IEEE-754 float format, if this signal is an IEEE float/double.
    pub float_format: Option<FloatFormat>,

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