Function extend_input_by_rand

hail-fuzz/src/mutations.rs:31–50

Extend an input by a random number of bytes exponentially distributed.

(
    rng: &mut R,
    factor: f64,
    dict: DictionaryRef,
    input: &mut Vec<u8>,
    extension_limit: usize,
)

/// Extend an input by a random number of bytes exponentially distributed.
pub(crate) fn extend_input_by_rand<R: Rng>(
    rng: &mut R,
    factor: f64,
    dict: DictionaryRef,
    input: &mut Vec<u8>,
    extension_limit: usize,
) -> Extension {
    // Small chance try a large extension up to the maximum limit.
    if rng.gen_bool(0.001) {
        return extend_input_by(rng, dict, input, extension_limit);
    }

    let dist = rand_distr::Exp::<f64>::new(LENGTH_EXTENSION_LAMBDA).unwrap();
    let base = (1 + (factor * dist.sample(rng).floor()) as usize).max(4);

    // Unless the input is small, avoid the extension from being more than twice the input length.
    let max_extension = (2 * input.len()).max(MIN_EXTENSION_LIMIT * (factor.floor() as usize));
    let amount = base.min(max_extension).min(extension_limit);
    extend_input_by(rng, dict, input, amount)
}

#[derive(Copy, Clone, Debug, serde::Serialize, serde::Deserialize)]
pub enum Extension {