qfall-math 0.1.1

Mathematical foundations for rapid prototyping of lattice-based cryptography
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// Copyright © 2023 Niklas Siemer
//
// This file is part of qFALL-math.
//
// qFALL-math is free software: you can redistribute it and/or modify it under
// the terms of the Mozilla Public License Version 2.0 as published by the
// Mozilla Foundation. See <https://mozilla.org/en-US/MPL/2.0/>.

//! This module contains algorithms for sampling
//! according to the binomial distribution.

use crate::{error::MathError, integer::Z, rational::Q, utils::sample::binomial::BinomialSampler};

impl Z {
    /// Chooses a [`Z`] instance according to the binomial distribution
    /// parameterized by `n` and `p`.
    ///
    /// Parameters:
    /// - `n`: specifies the number of trials
    /// - `p`: specifies the probability of success
    ///
    /// Returns a fresh [`Z`] instance with a value sampled
    /// according to the binomial distribution or a [`MathError`]
    /// if `n < 0`, `p ∉ (0,1)`, or `n` does not fit into an [`i64`].
    ///
    /// # Examples
    /// ```
    /// use qfall_math::integer::Z;
    ///
    /// let sample = Z::sample_binomial(2, 0.5).unwrap();
    /// ```
    ///
    /// # Errors and Failures
    /// - Returns a [`MathError`] of type [`InvalidIntegerInput`](MathError::InvalidIntegerInput)
    ///   if `n < 0`.
    /// - Returns a [`MathError`] of type [`InvalidInterval`](MathError::InvalidInterval)
    ///   if `p ∉ (0,1)`.
    /// - Returns a [`MathError`] of type [`ConversionError`](MathError::ConversionError)
    ///   if `n` does not fit into an [`i64`].
    pub fn sample_binomial(n: impl Into<Z>, p: impl Into<Q>) -> Result<Self, MathError> {
        let mut bin_sampler = BinomialSampler::init(n, p)?;

        Ok(bin_sampler.sample())
    }
}

#[cfg(test)]
mod test_sample_binomial {
    use super::{Q, Z};

    // As all major tests regarding an appropriate binomial distribution,
    // whether the correct interval is kept, and if the errors are thrown correctly,
    // are performed in the `utils` module, we omit these tests here.

    /// Checks whether `sample_binomial` is available for all types
    /// implementing [`Into<Z>`], i.e. u8, u16, u32, u64, i8, ...
    /// and [`Into<Q>`], i.e. u8, u16, i8, i16, f32, f64, ...
    #[test]
    fn availability() {
        let _ = Z::sample_binomial(1u16, 7u8);
        let _ = Z::sample_binomial(1u32, 7u16);
        let _ = Z::sample_binomial(1u64, 7u32);
        let _ = Z::sample_binomial(1i8, 7u64);
        let _ = Z::sample_binomial(1i16, 7i8);
        let _ = Z::sample_binomial(1i32, 7i16);
        let _ = Z::sample_binomial(1i64, 7i32);
        let _ = Z::sample_binomial(Z::ONE, 7i64);
        let _ = Z::sample_binomial(1u8, 0.5f32);
        let _ = Z::sample_binomial(1u8, 0.5f64);
        let _ = Z::sample_binomial(1, Q::from((1, 2)));
    }
}