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pub struct FunnelConfig;
impl FunnelConfig {
/// The OEIS 'stripped' file has sequences with variable length.
/// The average sequence length is 38 terms.
///
/// I rounded that up to 40, and made a funnel with 4 bloomfilters.
/// - The 1st bloomfilter checks 10 terms (0..9).
/// - The 2nd bloomfilter checks 20 terms (0..19).
/// - The 3rd bloomfilter checks 30 terms (0..29).
/// - The 4th bloomfilter checks 40 terms (0..39).
///
/// A candidate program must satisfy all the bloomfilters.
///
/// The sooner a candidate program can be rejected,
/// the sooner it's possible to mutate and try again.
pub const TERM_COUNT: usize = 40;
/// The OEIS 'stripped' file has half of its sequences with fewer than 38 terms.
/// Adjust this parameter, in order to add these short sequences to the bloomfilter.
pub const MINIMUM_NUMBER_OF_REQUIRED_TERMS: usize = 10;
/// As of july 2022, the OEIS database contains around 360k sequences.
/// So an approx count of 400k and there should be room for the near future.
pub const BLOOMFILTER_CAPACITY: usize = 400000;
/// The 'false-positive' rate is a percentage between `0.0001` and `1.0`.
///
/// This constant impacts how many hash operations that the bloomfilter is performing.
///
/// Picking a too low value, and the bloomfilter will have to do many hash operations.
/// This harms performance.
///
/// Picking a too high value, and the bloomfilter has only a few hash operations to do.
/// However there are lots of false positives.
///
/// There seems to be sweet spot around `1%`, with few false positives, but low performance.
///
/// Adjust this parameter, in order to tweak performace.
pub const BLOOMFILTER_FALSE_POSITIVE_RATE: f64 = 0.01;
/// Magic value to indicate that it's a wildcard term in the bloomfilter.
///
/// The rate of false-positives is impacted by this magic value.
/// Initially I had picked 0 as the magic value,
/// however I learned the hard way that 0 is the most popular term
/// in the OEIS 'stripped' file. This caused LOTS of programs to be generated,
/// most of them being false-positives.
///
/// To decide on a better magic value, I made a histogram of the terms
/// being used in the OEIS 'stripped' file. Only considering the values
/// in the range -400 and +400.
///
/// The value "-67" only occurs 85 times, and "-86" occurs 61 times,
/// so these may be good choices for a magic value.
///
/// It frequently happens that there is a collision with the magic value and
/// the actual term value in OEIS. This is not a problem, since this yields more
/// false positives. The magic value doesn't harm the ability to check if a value
/// is contained in the OEIS 'stripped' file.
pub const WILDCARD_MAGIC_VALUE: i32 = -86;
}
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