Function decode

nodedb-codec/src/double_delta.rs:155–219

Decode DoubleDelta-compressed bytes back to i64 values.

(data: &[u8])

/// Decode DoubleDelta-compressed bytes back to i64 values.
pub fn decode(data: &[u8]) -> Result<Vec<i64>, CodecError> {
    if data.len() < 4 {
        return Err(CodecError::Truncated {
            expected: 4,
            actual: data.len(),
        });
    }

    let count = u32::from_le_bytes(data[0..4].try_into().map_err(|_| CodecError::Corrupt {
        detail: "invalid header".into(),
    })?) as usize;

    if count == 0 {
        return Ok(Vec::new());
    }

    if data.len() < 12 {
        return Err(CodecError::Truncated {
            expected: 12,
            actual: data.len(),
        });
    }

    let first_value =
        i64::from_le_bytes(data[4..12].try_into().map_err(|_| CodecError::Corrupt {
            detail: "invalid first value".into(),
        })?);

    let mut values = Vec::with_capacity(count);
    values.push(first_value);

    if count == 1 {
        return Ok(values);
    }

    if data.len() < 20 {
        return Err(CodecError::Truncated {
            expected: 20,
            actual: data.len(),
        });
    }

    let first_delta =
        i64::from_le_bytes(data[12..20].try_into().map_err(|_| CodecError::Corrupt {
            detail: "invalid first delta".into(),
        })?);
    values.push(first_value.wrapping_add(first_delta));

    if count == 2 {
        return Ok(values);
    }

    let mut reader = BitReader::new(&data[20..]);
    let mut prev_delta = first_delta;

    for _ in 2..count {
        let dod = decode_dod(&mut reader)?;
        let delta = prev_delta.wrapping_add(dod);