qfall-math 0.2.0

// Copyright 2023 Jan 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 sampling algorithms for the uniform distributions.

use crate::{
    integer::Z,
    integer_mod_q::MatZq,
    macros::seeded::seedable_function,
    traits::{MatrixDimensions, MatrixSetEntry},
    utils::sample::uniform::UniformIntegerSampler,
};
use std::fmt::Display;

impl MatZq {
    seedable_function!(
        /// Outputs a [`MatZq`] instance with entries chosen uniform at random
        /// in `[0, modulus)`.
        ///
        /// The internally used uniform at random chosen bytes are generated
        #[unseeded]
        /// by [`ThreadRng`](rand::rngs::ThreadRng), which uses ChaCha12 and is
        #[seeded]
        /// by a [`StdRng`](rand::rngs::StdRng) seeded with `seed`, which uses ChaCha12 and is
        #[optionally_seeded]
        /// by a [`StdRng`](rand::rngs::StdRng) seeded with `seed` or by [`ThreadRng`](rand::rngs::ThreadRng)
        #[optionally_seeded]
        /// if `seed` is `None`. Both use ChaCha12 and are
        /// considered cryptographically secure.
        ///
        /// Parameters:
        /// - `num_rows`: specifies the number of rows the new matrix should have
        /// - `num_cols`: specifies the number of columns the new matrix should have
        /// - `modulus`: specifies the modulus of the matrix and defines the interval
        ///   over which is sampled
        #[seeded]
        /// - `seed`: specifies the 256-bit seed of the PRNG used for sampling
        #[optionally_seeded]
        /// - `seed`: specifies an optional 256-bit seed of the PRNG used for sampling.
        #[optionally_seeded]
        ///   If `None` is provided, a fresh [`ThreadRng`](rand::rngs::ThreadRng) is used instead.
        ///
        /// Returns a new [`MatZq`] instance with entries chosen
        /// uniformly at random in `[0, modulus)`.
        ///
        /// # Examples
        /// ```
        /// use qfall_math::integer_mod_q::MatZq;
        ///
        #[unseeded]
        /// let matrix = MatZq::sample_uniform(3, 3, 17);
        #[seeded]
        /// let matrix = MatZq::sample_uniform_seeded(3, 3, 17, [42; 32]);
        /// ```
        ///
        /// # Panics ...
        /// - if the provided number of rows and columns or the modulus are not suited to create a matrix.
        ///   For further information see [`MatZq::new`].
        pub(crate) fn sample_uniform(
            num_rows: impl TryInto<i64> + Display,
            num_cols: impl TryInto<i64> + Display,
            modulus: impl Into<Z>,
            seed: Option<[u8; 32]>,
        ) -> Self {
            let modulus: Z = modulus.into();
            let mut uis = UniformIntegerSampler::init(&modulus, seed).unwrap();
            let mut matrix = MatZq::new(num_rows, num_cols, modulus);

            for row in 0..matrix.get_num_rows() {
                for col in 0..matrix.get_num_columns() {
                    let sample = uis.sample();
                    unsafe { matrix.set_entry_unchecked(row, col, sample) };
                }
            }

            matrix
        }
    );
}

#[cfg(test)]
mod test_sample_uniform {
    use crate::traits::{MatrixDimensions, MatrixGetEntry};
    use crate::utils::sample::test_seed;
    use crate::{
        integer::Z,
        integer_mod_q::{MatZq, Modulus},
    };

    /// Checks whether the boundaries of the interval are kept for small moduli.
    #[test]
    fn boundaries_kept_small() {
        for seeded in [false, true] {
            for _ in 0..32 {
                let matrix =
                    MatZq::sample_uniform_optionally_seeded(1, 1, 17, seeded.then(test_seed));
                let sample: Z = matrix.get_entry(0, 0).unwrap();
                assert!(Z::ZERO <= sample);
                assert!(sample < 17);
            }
        }
    }

    /// Checks whether the boundaries of the interval are kept for large moduli.
    #[test]
    fn boundaries_kept_large() {
        for seeded in [false, true] {
            let modulus = Z::from(u64::MAX);
            for _ in 0..256 {
                let matrix =
                    MatZq::sample_uniform_optionally_seeded(1, 1, &modulus, seeded.then(test_seed));
                let sample: Z = matrix.get_entry(0, 0).unwrap();
                assert!(Z::ZERO <= sample);
                assert!(sample < modulus);
            }
        }
    }

    /// Checks whether matrices with at least one dimension chosen smaller than `1`
    /// or too large for an [`i64`] results in a panic.
    #[test]
    fn false_size() {
        for seeded in [false, true] {
            let result = std::panic::catch_unwind(|| {
                let modulus = Z::from(15);

                let _ =
                    MatZq::sample_uniform_optionally_seeded(0, 3, &modulus, seeded.then(test_seed));
            });
            assert!(result.is_err());
        }
    }

    /// Checks whether providing an invalid interval/ modulus results in a panic.
    #[test]
    fn invalid_modulus() {
        for seeded in [false, true] {
            let result = std::panic::catch_unwind(|| {
                let _ = MatZq::sample_uniform_optionally_seeded(4, 1, 1, seeded.then(test_seed));
            });
            assert!(result.is_err());
        }
    }

    /// Checks whether `sample_uniform` is available for all types
    /// implementing [`Into<Z>`], i.e. u8, u16, u32, u64, i8, ...
    #[test]
    fn availability() {
        for seeded in [false, true] {
            let modulus = Modulus::from(7);
            let z = Z::from(7);

            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7u8, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7u16, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7u32, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7u64, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7i8, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7i16, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7i32, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, 7i64, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, &modulus, seeded.then(test_seed));
            let _ = MatZq::sample_uniform_optionally_seeded(1, 1, &z, seeded.then(test_seed));

            // explicitly checks the existence of the unseeded and the seeded function
            if seeded {
                let _ = MatZq::sample_uniform_seeded(1, 1, 7u8, test_seed());
            } else {
                let _ = MatZq::sample_uniform(1, 1, 7u8);
            }
        }
    }

    /// Checks whether the size of uniformly random sampled matrices
    /// fits the specified dimensions.
    #[test]
    fn matrix_size() {
        for seeded in [false, true] {
            let modulus = Z::from(15);

            let mat_0 =
                MatZq::sample_uniform_optionally_seeded(3, 3, &modulus, seeded.then(test_seed));
            let mat_1 =
                MatZq::sample_uniform_optionally_seeded(4, 1, &modulus, seeded.then(test_seed));
            let mat_2 =
                MatZq::sample_uniform_optionally_seeded(1, 5, &modulus, seeded.then(test_seed));
            let mat_3 =
                MatZq::sample_uniform_optionally_seeded(15, 20, &modulus, seeded.then(test_seed));

            assert_eq!(3, mat_0.get_num_rows());
            assert_eq!(3, mat_0.get_num_columns());
            assert_eq!(4, mat_1.get_num_rows());
            assert_eq!(1, mat_1.get_num_columns());
            assert_eq!(1, mat_2.get_num_rows());
            assert_eq!(5, mat_2.get_num_columns());
            assert_eq!(15, mat_3.get_num_rows());
            assert_eq!(20, mat_3.get_num_columns());
        }
    }

    /// Checks whether the same seed results in the same sample.
    #[test]
    fn same_seed_same_sample() {
        use crate::integer_mod_q::MatZq;
        let sample_0 = MatZq::sample_uniform_seeded(3, 3, 17, [42; 32]);
        let sample_1 = MatZq::sample_uniform_seeded(3, 3, 17, [42; 32]);

        assert_eq!(sample_0, sample_1);
    }

    /// Checks whether the seeded variant outputs the known sample for a fixed seed.
    #[test]
    fn known_answer() {
        use crate::integer_mod_q::MatZq;
        let sample = MatZq::sample_uniform_seeded(3, 3, 17, [42; 32]);

        assert_eq!(
            "[[2, 16, 3],[7, 7, 16],[4, 13, 0]] mod 17",
            sample.to_string()
        );
    }
}