qfall_math/integer_mod_q/z_q/

from.rs

// Copyright © 2023 Sven Moog, Marcel Luca Schmidt, 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/>.

//! Implementations to create a [`Zq`] value from other types.
//!
//! The explicit functions contain the documentation.

use super::Zq;
use crate::{
    error::{MathError, StringConversionError},
    integer::Z,
    integer_mod_q::Modulus,
};
use std::str::FromStr;

impl<Mod: Into<Modulus>> From<Mod> for Zq {
    /// Creates a zero integer with a given [`Modulus`].
    ///
    /// Parameters:
    /// - `modulus`: of the new [`Zq`]
    ///
    /// Returns a new constant [`Zq`] with the specified [`Modulus`].
    ///
    /// # Examples
    /// ```
    /// use qfall_math::integer_mod_q::Zq;
    /// use std::str::FromStr;
    ///
    /// let zq = Zq::from(100);
    ///
    /// let zq_cmp = Zq::from_str("0 mod 100").unwrap();
    /// assert_eq!(zq, zq_cmp);
    /// ```
    ///
    /// # Panics ...
    /// - if `modulus` is smaller than `2`.
    fn from(modulus: Mod) -> Self {
        let value = Z::default();
        let modulus = modulus.into();

        let mut out = Zq { value, modulus };
        out.reduce();
        out
    }
}

impl<IntegerValue: Into<Z>, IntegerModulus: Into<Modulus>> From<(IntegerValue, IntegerModulus)>
    for Zq
{
    /// Creates a [`Zq`] from a tuple with the integer and the modulus.
    ///
    /// Parameters:
    /// - `value`: Defines the value of the residue class.
    /// - `modulus`: Defines the modulus by which `value` is reduced.
    ///
    /// Note that the strings for integer and modulus are trimmed,
    /// i.e. all whitespaces around all values are ignored.
    ///
    /// Returns the `value` mod `modulus` as a [`Zq`].
    ///
    /// # Examples
    /// ```
    /// use qfall_math::integer_mod_q::Zq;
    /// use qfall_math::integer::Z;
    ///
    /// let answer_1 = Zq::from((1337 + 42, 1337));
    /// let answer_2 = Zq::from((Z::from(42), 1337));
    ///
    /// assert_eq!(answer_1, answer_2);
    /// ```
    ///
    /// # Panics ...
    /// - if `modulus` is smaller than `2`.
    fn from((value, modulus): (IntegerValue, IntegerModulus)) -> Self {
        let value = value.into();
        let modulus = modulus.into();

        let mut out = Zq { value, modulus };
        out.reduce();
        out
    }
}

impl FromStr for Zq {
    type Err = MathError;

    /// Creates a [`Zq`] integer from a [`String`].
    ///
    /// Parameters:
    /// - `s`: the integer and modulus value of form: `"12 mod 25"` for the number 12
    ///   under the modulus 25.
    ///
    /// Returns a [`Zq`] or an error if the provided string was not formatted
    /// correctly.
    ///
    /// # Examples
    /// ```
    /// use std::str::FromStr;
    /// use qfall_math::integer_mod_q::Zq;
    ///  
    /// let a: Zq = "100 mod 3".parse().unwrap();
    /// let b: Zq = Zq::from_str("100 mod 3").unwrap();
    /// ```
    ///
    /// # Errors and Failures
    /// - Returns a [`MathError`] of type
    ///   [`StringConversionError`](MathError::StringConversionError)
    ///     - if the provided string contains a `Null` byte,
    ///     - if the provided string was not formatted correctly,
    ///     - if the provided modulus was not formatted correctly to create a [`Z`], or
    ///     - if the delimiter `mod` could not be found.
    /// - Returns a [`MathError`] of type
    ///   [`InvalidModulus`](MathError::InvalidModulus)
    ///   if the provided value is smaller than `2`.
    /// - Returns a [`MathError`] of type
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let input_split: Vec<&str> = s.split("mod").collect();
        if input_split.len() != 2 {
            return Err(StringConversionError::InvalidStringToZqInput(s.to_owned()))?;
        }

        // instantiate both parts of Zq element
        let modulus = Modulus::from_str(input_split[1].trim())?;
        let value = Z::from_str(input_split[0].trim())?;

        let mut out = Self { value, modulus };
        out.reduce();

        Ok(out)
    }
}

impl From<&Zq> for Zq {
    /// An alias for [`Zq::clone`].
    /// It makes the use of generic `Into<Zq>` types easier.
    fn from(value: &Zq) -> Self {
        value.clone()
    }
}

impl Zq {
    /// Create a [`Zq`] integer from a [`String`], i.e. its UTF8-Encoding.
    /// The inverse of this function is [`Zq::to_utf8`].
    ///
    /// Parameters:
    /// - `message`: specifies the message that is transformed via its UTF8-Encoding
    ///   to a new [`Zq`] instance.
    /// - `modulus`: Defines the modulus by which `value` is reduced.
    ///
    /// Returns value defined by `message` mod `modulus` as [`Zq`] or a [`MathError`]
    /// if the provided modulus is smaller than the UTF8-Encoding of the message.
    ///
    /// # Examples
    /// ```
    /// use qfall_math::integer_mod_q::Zq;
    /// let message = "hello!";
    ///  
    /// let value = Zq::from_utf8(&message, i64::MAX).unwrap();
    /// assert_eq!(Zq::from((36762444129640u64, i64::MAX)), value);
    /// ```
    ///
    /// # Errors and Failures
    /// - Returns a [`ConversionError`](MathError::ConversionError) if the provided modulus
    ///   is smaller than the UTF8-Encoding of the message.
    ///
    /// # Panics ...
    /// - if `modulus` is smaller than `2`.
    pub fn from_utf8(message: &str, modulus: impl Into<Modulus>) -> Result<Zq, MathError> {
        let modulus: Modulus = modulus.into();
        let modulus_as_z: Z = (&modulus).into();
        let value = Z::from_utf8(message);

        if modulus_as_z > value {
            return Ok(Zq::from((value, &modulus)));
        }
        Err(MathError::ConversionError(
            "The provided modulus is smaller than the UTF8-Encoding of your message.".to_owned(),
        ))
    }
}

#[cfg(test)]
mod test_from_mod {
    use crate::integer_mod_q::Zq;
    use std::str::FromStr;

    /// Ensure that the resulting value is zero and the modulus is correctly instantiated.
    #[test]
    fn modulus_zero() {
        let zq = Zq::from(100);

        assert_eq!(zq, Zq::from_str("0 mod 100").unwrap());
    }

    /// Ensure that initializing large moduli works.
    #[test]
    fn modulus_large() {
        let zq = Zq::from(u64::MAX);

        assert_eq!(zq, Zq::from_str(&format!("0 mod {}", u64::MAX)).unwrap());
    }

    /// Ensure that mod 0 results in a panic.
    #[test]
    #[should_panic]
    fn modulus_0() {
        let _ = Zq::from(0);
    }

    /// Ensure that mod 1 results in a panic.
    #[test]
    #[should_panic]
    fn modulus_1() {
        let _ = Zq::from(1);
    }

    /// Ensure that a negative modulus results in a panic.
    #[test]
    #[should_panic]
    fn modulus_negative() {
        let _ = Zq::from(-1);
    }
}

#[cfg(test)]
mod test_from_trait {
    use crate::{
        integer::Z,
        integer_mod_q::{Modulus, Zq},
    };

    /// Test that the different combinations of rust integers, [`Z`], and [`Modulus`]
    /// in their owned and borrowed form can be used to create a [`Zq`].
    #[test]
    fn different_types() {
        let int_8: i8 = 10;
        let int_16: i16 = 10;
        let int_32: i32 = 10;
        let int_64: i64 = 10;
        let uint_8: u8 = 10;
        let uint_16: u16 = 10;
        let uint_32: u32 = 10;
        let uint_64: u64 = 10;
        let z = Z::from(10);
        let modulus = Modulus::from(10);

        // owned, owned the same type in numerator and denominator
        let _ = Zq::from((int_8, int_8));
        let _ = Zq::from((int_16, int_16));
        let _ = Zq::from((int_32, int_32));
        let _ = Zq::from((int_64, int_64));
        let _ = Zq::from((uint_8, uint_8));
        let _ = Zq::from((uint_16, uint_16));
        let _ = Zq::from((uint_32, uint_32));
        let _ = Zq::from((uint_64, uint_64));
        let _ = Zq::from((z.clone(), z.clone()));
        let _ = Zq::from((modulus.clone(), modulus.clone()));

        // borrowed, borrowed the same type in numerator and denominator
        let _ = Zq::from((&int_8, &int_8));
        let _ = Zq::from((&int_16, &int_16));
        let _ = Zq::from((&int_32, &int_32));
        let _ = Zq::from((&int_64, &int_64));
        let _ = Zq::from((&uint_8, &uint_8));
        let _ = Zq::from((&uint_16, &uint_16));
        let _ = Zq::from((&uint_32, &uint_32));
        let _ = Zq::from((&uint_64, &uint_64));
        let _ = Zq::from((&z, &z));
        let _ = Zq::from((&modulus, &modulus));

        // From now on assume that i/u8, i/u16, i/u32 and i/u64 behave the same.
        // This assumption is reasonable, since their implementation is the same.

        // owned, owned mixed types
        let _ = Zq::from((int_8, z.clone()));
        let _ = Zq::from((z.clone(), int_8));
        let _ = Zq::from((int_8, modulus.clone()));
        let _ = Zq::from((z.clone(), modulus.clone()));
        let _ = Zq::from((modulus.clone(), int_8));
        let _ = Zq::from((modulus.clone(), z.clone()));

        // owned, borrowed mixed types
        let _ = Zq::from((int_8, &z));
        let _ = Zq::from((modulus.clone(), &z));
        let _ = Zq::from((z.clone(), &int_8));
        let _ = Zq::from((z.clone(), &modulus));
        let _ = Zq::from((int_8, &modulus));
        let _ = Zq::from((modulus.clone(), &int_8));

        // borrowed, owned mixed types
        let _ = Zq::from((&int_8, z.clone()));
        let _ = Zq::from((&modulus, z.clone()));
        let _ = Zq::from((&z, int_8));
        let _ = Zq::from((&z, modulus.clone()));
        let _ = Zq::from((&int_8, modulus.clone()));
        let _ = Zq::from((&modulus, int_8));

        // borrowed, borrowed mixed types
        let _ = Zq::from((&int_8, &z));
        let _ = Zq::from((&modulus, &z));
        let _ = Zq::from((&z, &int_8));
        let _ = Zq::from((&z, &modulus));
        let _ = Zq::from((&int_8, &modulus));
        let _ = Zq::from((&modulus, &int_8));
    }

    /// Ensure that the modulus calculation is performed at initialization.
    #[test]
    fn modulus_at_initialization() {
        let a = Zq::from((0, 10));
        let b = Zq::from((10, 10));

        assert_eq!(a, b);
    }

    /// Test with small valid value and modulus.
    #[test]
    fn working_small() {
        let zq_1 = Zq::from((10, 15));
        let zq_2 = Zq::from((Z::from(10), Modulus::from(15)));

        assert_eq!(zq_1, zq_2);
    }

    /// Test with large value and modulus (FLINT uses pointer representation).
    #[test]
    fn working_large() {
        let zq_1 = Zq::from((u64::MAX - 1, u64::MAX));
        let zq_2 = Zq::from((&Z::from(u64::MAX - 1), Modulus::from(u64::MAX)));

        assert_eq!(zq_1, zq_2);
    }

    /// Test with `0` modulus (not valid)
    #[test]
    #[should_panic]
    fn modulus_zero() {
        let _ = Zq::from((10, 0));
    }

    /// Test with negative modulus (not valid)
    #[test]
    #[should_panic]
    fn modulus_negative() {
        let _ = Zq::from((10, -1));
    }
}

#[cfg(test)]
mod tests_from_str {
    use crate::integer_mod_q::Zq;
    use std::str::FromStr;

    /// Ensure that initialization with large numbers works.
    #[test]
    fn max_int_positive() {
        assert!(Zq::from_str(&format!("{} mod {}", i64::MAX, u64::MAX)).is_ok());
    }

    /// Ensure that initialization with large numbers (larger than [`i64`]) works.
    #[test]
    fn large_positive() {
        assert!(Zq::from_str(&format!("{} mod {}", u64::MAX, u128::MAX)).is_ok());
    }

    /// Ensure that initialization with large negative numbers works.
    #[test]
    fn max_int_negative() {
        assert!(Zq::from_str(&format!("-{} mod {}", i64::MAX, u64::MAX)).is_ok());
    }

    /// Ensure that initialization with large negative numbers (larger than [`i64`]) works.
    #[test]
    fn large_negative() {
        assert!(Zq::from_str(&format!("-{} mod {}", u64::MAX, u128::MAX)).is_ok());
    }

    /// Ensure that initialization with standard values works.
    #[test]
    fn normal_value() {
        assert!(Zq::from_str("42 mod 5").is_ok());
    }

    /// Ensure that initialization works with leading and trailing whitespaces.
    #[test]
    fn whitespaces_work() {
        assert!(Zq::from_str("    42 mod 5").is_ok());
        assert!(Zq::from_str("42 mod 5    ").is_ok());
        assert!(Zq::from_str("42    mod 5").is_ok());
        assert!(Zq::from_str("42 mod     5").is_ok());
    }

    /// Ensure that initialization yields an error with whitespaces in between.
    #[test]
    fn whitespaces_error() {
        assert!(Zq::from_str("4 2 mod 5").is_err());
        assert!(Zq::from_str("42 mo d 5").is_err());
        assert!(Zq::from_str("42 mod 5 0").is_err());
    }

    /// Ensure that wrong initialization yields an Error.
    #[test]
    fn error_wrong_letters() {
        assert!(Zq::from_str("hbrkt35itu3gg").is_err());
        assert!(Zq::from_str("3-2 mod 3").is_err());
        assert!(Zq::from_str("3 5").is_err());
        assert!(Zq::from_str("3%5").is_err());
        assert!(Zq::from_str("3/5 mod 3").is_err());
    }
}

#[cfg(test)]
/// Test the implementation of [`Zq::from_utf8`] briefly.
/// This module omits tests that were already provided for [`crate::integer::Z::from_utf8`].
mod test_from_utf8 {
    use super::Zq;

    /// Ensures that values that are larger than the modulus result in an error.
    #[test]
    fn not_enough_memory() {
        let message = "some_long message with too many bytes";
        let modulus = u32::MAX;

        let value = Zq::from_utf8(message, modulus);

        assert!(value.is_err());
    }

    /// Ensures that using a modulus smaller than `2` results in a panic.
    #[test]
    #[should_panic]
    fn modulus_too_small() {
        let message = "something";
        let modulus = 1;

        let _ = Zq::from_utf8(message, modulus);
    }
}